Field Guide to California Insects: Second Edition
By Kip Will
()
About this ebook
Completely revised for the first time in over 40 years, Field Guide to California Insects now includes over 600 insect species, each beautifully illustrated with color photographs. Engaging accounts focus on distinguishing features, remarkable aspects of biology, and geographical distribution in the state. An accessible and compact introduction to identifying, understanding, and appreciating these often unfamiliar and fascinating creatures, this guide covers insects that readers are likely to encounter in homes and natural areas, cities and suburbs, rural lands and wilderness. It also addresses exotic and invasive species and their impact on native plants and animals. Field Guide to California Insects remains the definitive portable reference and a captivating read for beginners as well as avid naturalists.
Kip Will
Kip Will is an entomologist, insect systematist, and former director of the Essig Museum of Entomology at the University of California, Berkeley. Joyce Gross has been photographing California insects for 17 years and works as a computer programmer with the Berkeley Natural History Museums at the University of California, Berkeley. Dan Rubinoff is Professor of Entomology and Director of the University of Hawaii Insect Museum. He grew up in California chasing insects and continues to work actively in the state. Jerry A. Powell is Professor of the Graduate School and former director of the Essig Museum of Entomology at the University of California, Berkeley.
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Field Guide to California Insects - Kip Will
Field Guide to California Insects
California Natural History Guides
Phyllis M. Faber and Bruce M. Pavlik, General Editors
FIELD GUIDE TO CALIFORNIA INSECTS
SECOND EDITION
Kip Will
Joyce Gross
Daniel Rubinoff
Jerry A. Powell
UC LogoUNIVERSITY OF CALIFORNIA PRESS
Oak Treehopper (Platycotis vittata), image by J. Gross.
California Natural History Guides No. 111
University of California Press
Oakland, California
© 2020 by The Regents of the University of California
Library of Congress Cataloging-in-Publication Data
Names: Will, Kipling, 1964– author. | Gross, Joyce (Linda Joyce), author. | Rubinoff, Daniel (Entomologist), author. | Powell, Jerry A., author. | Powell, Jerry A. California insects. 1979
Title: Field guide to California insects / Kip Will, Joyce Gross, Daniel Rubinoff, Jerry A. Powell.
Other titles: California natural history guides ; 111.
Description: Second edition. | Oakland, California : University of California Press, [2020] | Series: California natural history guides ; no. 111 | Includes bibliographical references and index.
Identifiers: LCCN 2020016309 (print) | LCCN 2020016310 (ebook) | ISBN 9780520288737 (cloth) | ISBN 9780520288744 (paperback) | ISBN 9780520963573 (ebook)
Subjects: LCSH: Insects—California.
Classification: LCC QL475.C2 W55 2020 (print) | LCC QL475.C2 (ebook) | DDC 595.709794—dc23
LC record available at https://lccn.loc.gov/2020016309
LC ebook record available at https://lccn.loc.gov/2020016310
Manufactured in the United States of America
28 27 26 25 24 23 22 21 20
10 9 8 7 6 5 4 3 2 1
Cover illustrations, clockwise from upper left :
Pleasant Plant Bug (Closterocoris amoenus), image by J. Gross.
California Tide-walker (Thalassotrechus barbarae), image by J. Gross.
Brick-red Thick-headed Fly (Myopa rubida), image by J. Gross.
Electra Buck Moth (Hemileuca electra), image by Kirby Wolfe.
The publisher and the University of California Press Foundation gratefully acknowledge the generous support of the Ralph and Shirley Shapiro Endowment Fund in Environmental Studies.
Little Bear (Paracotalpa ursina), image by J. Gross.
CONTENTS
List of Plates
Preface
INTRODUCTION
What Is an Insect?
Growth and Reproduction
Breathing and Circulation
Feeding
Stinging
Distribution and Diversity of the California Insect Fauna
Topography
Geographical Distribution
Diversity
Microhabitats
Making an Insect Collection
Classification
Names
Synopsis of Hexapods and the Orders of Insects
ACCOUNTS: SYSTEMATIC TREATMENT
Coneheads (Class Protura)
Two-pronged Bristletails (Class Diplura)
Springtails (Class Collembola)
Insects (Class Insecta)
Bristletails (Order Archaeognatha)
Silverfish (Order Zygentoma)
Mayflies (Order Ephemeroptera)
Dragonflies and Damselflies (Order Odonata)
Stoneflies (Order Plecoptera)
Ice Crawlers (Order Grylloblattodea)
Cockroaches and Termites (Order Blattodea)
Mantises (Order Mantodea)
Grasshoppers, Crickets, and Katydids (Order Orthoptera)
Walking Sticks (Order Phasmida)
Webspinners (Order Embiidina)
Earwigs (Order Dermaptera)
Barklice, Booklice, and Parasitic Lice (Order Psocodea)
True Bugs, Hoppers, Aphids, Scales, and Other Bugs (Order Hemiptera)
Thrips (Order Thysanoptera)
Fishflies and Alderflies (Order Megaloptera)
Snakeflies (Order Raphidioptera)
Nerve-winged Insects (Order Neuroptera)
Stylops (Order Strepsiptera)
Beetles (Order Coleoptera)
Fleas (Order Siphonaptera)
Flies, Gnats, and Midges (Order Diptera)
Scorpionflies (Order Mecoptera)
Caddisflies (Order Trichoptera)
Moths and Butterflies (Order Lepidoptera)
Ants, Wasps, and Bees (Order Hymenoptera)
Acknowledgments
Glossary
Bibliography
Online Resources
Photo Credits
Index
About the Authors
PLATES
Wingless Hexapods (Protura / Diplura / Collembola)
Plate 1
Bristletails (Archaeagnatha) & Silverfish (Zygentoma)
Plate 2
Silverfish (Zygentoma) & Mayflies (Ephemeroptera)
Plate 3
Mayflies (Ephemeroptera)
Plate 4
Plate 5
Dragonflies and Damselflies (Odonata)
Plate 6
Plate 7
Plate 8
Plate 9
Plate 10
Dragonflies and Damselflies (Odonata) & Stoneflies (Plecoptera)
Plate 11
Stoneflies (Plecoptera) & Rock Crawlers (Grylloblattodea)
Plate 12
Cockroaches and Termites (Blattodea)
Plate 13
Plate 14
Plate 15
Plate 16
Plate 17
Mantises (Mantodea)
Plate 18
Mantises (Mantodea) & Grasshoppers, Crickets, and Katydids (Orthoptera)
Plate 19
Grasshoppers, Crickets, and Katydids (Orthoptera)
Plate 20
Plate 21
Plate 22
Plate 23
Plate 24
Plate 25
Plate 26
Plate 27
Walkingsticks (Phasmida)
Plate 28
Webspinners (Embiidina) & Earwigs (Dermaptera)
Plate 29
Barklice, Booklice, and Parasitic Lice (Psocodea)
Plate 30
Plate 31
True Bugs, Hoppers, Aphids, Scales, and Other Bugs (Hemiptera)
Plate 32
Plate 33
Plate 34
Plate 35
Plate 36
Plate 37
Plate 38
Plate 39
Plate 40
Plate 41
Plate 42
Plate 43
Plate 44
Plate 45
Plate 46
Plate 47
Plate 48
Thrips (Thysanoptera)
Plate 49
Fishflies and Alderflies (Megaloptera) & Snakeflies (Raphidioptera)
Plate 50
Nerve-Winged Insects (Neuroptera)
Plate 51
Plate 52
Plate 53
Nerve-Winged Insects (Neuroptera) & Stylops (Strepsiptera)
Plate 54
Beetles (Coleoptera)
Plate 55
Plate 56
Plate 57
Plate 58
Plate 59
Plate 60
Plate 61
Plate 62
Plate 63
Plate 64
Plate 65
Plate 66
Plate 67
Plate 68
Plate 69
Plate 70
Plate 71
Plate 72
Plate 73
Plate 74
Plate 75
Plate 76
Plate 77
Plate 78
Fleas (Siphonaptera)
Plate 79
Gnats, Midges, and Flies (Diptera)
Plate 80
Plate 81
Plate 82
Plate 83
Plate 84
Plate 85
Plate 86
Plate 87
Plate 88
Plate 89
Plate 90
Plate 91
Plate 92
Plate 93
Plate 94
Plate 95
Plate 96
Plate 97
Plate 98
Plate 99
Plate 100
Scorpionflies (Mecoptera)
Plate 101
Caddisflies (Trichoptera)
Plate 102
Plate 103
Plate 104
Plate 105
Moths and Butterflies (Lepidoptera)
Plate 106
Plate 107
Plate 108
Plate 109
Plate 110
Plate 111
Plate 112
Plate 113
Plate 114
Plate 115
Plate 116
Plate 117
Plate 118
Plate 119
Plate 120
Plate 121
Plate 122
Plate 123
Plate 124
Plate 125
Plate 126
Plate 127
Ants, Wasps, and Bees (Hymenoptera)
Plate 128
Plate 129
Plate 130
Plate 131
Plate 132
Plate 133
Plate 134
Plate 135
Plate 136
Plate 137
Plate 138
Plate 139
Plate 140
Plate 141
Plate 142
Plate 143
PREFACE
Many naturalists are surprised at the diversity of insect life, only a few people have a broad appreciation of it, and many are skeptical when they hear the estimated numbers of insect species for a given natural community or geographical region. About one million described species of insects are known, more than five times the number of all other animals combined. Estimates of the number remaining to be discovered and named vary between three million to 30 million or more. Discrepancies in such estimates are due primarily to the poor state of knowledge concerning tropical communities and many difficult-to-sample habitats, such as the deep soil, worldwide. Even in California, the discovery of morphologically distinct, new species is commonplace; with each family inventoried by specialists during the past 40 years, 10 percent to 40 percent of the species have been discovered to be new. Only with quite well-known large insects that are popular with collectors, such as dragonflies, butterflies, and large moths, are we relatively sure that the inventory is nearing completion.
For example, very few new species of butterflies have been described from California since the first edition of this field guide and for those that were, recognition relied on DNA data to establish species from morphologically similar or polymorphic populations. There is no list of all insect species recorded in the state, but by comparing the numbers in families of various taxa that we are familiar with and by informally polling various experts, a figure of 30,000 to 40,000 species emerges as a conservative estimate for all the insect species in California. Therefore, it is obvious that a small book cannot treat all California insects. Whereas pocket guides can be developed with species treatments for a group that includes only several dozen or a few hundred species (such as California’s birds, amphibians and reptiles, cacti, etc.), comparable treatment of all insects would fill many volumes—a prospect that is neither practical in terms of cost nor possible in terms of available knowledge and expertise.
The primary problem in planning this work, encountered at the outset, was: How does one summarize knowledge on 40,000 species of insects? Choosing which insects to exclude was an agonizing process. This guide is meant to cover some but not nearly all of the spectacular diversity Californians may encounter. We decided to select about 600 of the most common and interesting kinds, and to discuss the biology, natural history, and diagnostic features of each, letting this small sample represent the whole diversity. Given this sample, there is no doubt that readers will find some conspicuous insects, common in a given region or at a particular time of year, omitted from our treatment. Smaller, more obscure groups are characterized at the family level, while more conspicuous insects and those of importance to humans are treated in more detail with representative species or genera. Each of these entities is illustrated with one or more photographs. The selection mixes many insects that will be encountered easily with some that are rarely seen, but the latter are worth the effort it takes to find them and witness firsthand their wonderful and peculiar forms and behaviors. These rarer species are included as something of a challenge to readers to go out on their own expeditions and try to find some of California’s amazing but little-seen insects.
This introductory guide to identification and natural history of California insects does not attempt to compile all information on any of the species discussed nor to present technical information on other fields of entomology. As a gateway to insect diversity and a general reference for groups, the guide is not intended to show their complete diversity. It is written for the general public and beginning students of entomology. We hope that the format encourages you to read the book and build a general familiarity with and passion for the insects that share California with us. There are several excellent, detailed, oft en species-level field guides for specific groups, such as bees, beetles, dragonflies and damselflies, and butterflies, and we encourage anyone with a strong interest in a specific group to seek these out. Likewise, there are excellent textbooks on entomology that cover details and vocabulary of morphology and collection-building methods in a way not possible in the field guide format. These sources are now augmented by a significant and growing wealth of information online.
Our identifications of specimens and statements on the natural history, biology, and geographical distributions of the included species are based on and informed by our work and literature accounts as well as on collections of the California Academy of Sciences, San Francisco; the Los Angeles County Museum of Natural History; the University of California at Berkeley; the University of California at Davis; and the University of California at Riverside. We have also received substantial advice from our colleagues and the entomology community at large, especially through a number of online forums such as BugGuide.
Note that in the color plates insects are not shown to the same scale even on the same page. Readers should refer to the species accounts where the size of the insects is given. Images may appear immediately before or after a given species account and so each image number has an adjacent arrow (◄ or ►), oriented to indicate which direction to look for the referenced images. The abbreviation BL is used throughout for body length. Most size ranges refer to the apparent length of the insect from the front of the head to the tip of the abdomen. For insects with wings that reach the tip of the abdomen, the wings are included in the body length. In some cases we specifically refer to wing width or the length including wings.
INTRODUCTION
Lubberly Band-winged Grasshopper (Agymnastus ingens), image by J. Gross.
What Is an Insect?
Insects occur everywhere except in the high polar regions and below the surface of the oceans. A few species have even adapted to life on the Antarctic shelf margins; on cold, subarctic islands; in intertidal zones; and on the surface of the open ocean. Insects live in great abundance at every ecological horizon on land and in freshwater—in soil, where many feed on decaying organic matter and fungi or on plant roots; on ancient, low-growing plants such as mosses and ferns; on or in the trunks of shrubs and trees; and on or in foliage, flowers, or seeds of flowering plants. At each of these horizons, there is a complex of insects, each living in its own way, as a scavenger, primary consumer of plant material, predator, or parasite of other insects or other animals, and so on. Among both plant feeders and parasites, there are some generalist feeders and some that show great specialization for particular hosts.
Growth and Reproduction
In most insects, males and females are produced in about equal numbers, mating occurs, and females deposit eggs on or near the food used by the young. There are many modifications of this basic pattern—males may be produced only at certain seasons, as in social insects; generations of females may be produced without mating (parthenogenesis) while environmental conditions are favorable, as in aphids; or sexual forms are lost altogether, a phenomenon known in certain weevils, moths, and other insects. In typical forms, the sexes locate one another extremely effectively, and most females are mated almost as soon as they emerge. Commonly, the attraction of mates is accomplished using a volatile chemical or scent (pheromone) broadcast in the air, usually by the female. In some insects, such as butterflies and fireflies, visual perception of the mate is necessary; in others, like crickets and cicadas, calls or other sounds are perceived by one or both mates.
Adult insects do not grow. Growth occurs through a series of stages (instars) in juveniles; at the end of each, the shell or skin is shed (molted), and the new, temporarily pliable stage of the insect enlarges. After the final juvenile instar, molting produces the adult stage. In the simplest life cycle (hemimetabolous), such as that of roaches and grasshoppers, the eggs hatch into tiny nymphs resembling the adults except that they are smaller and lack wings and reproductive organs. Most insects have a more complex life cycle, normally with four stages (holometabolous—a complete change or metamorphosis): adults lay eggs that hatch into caterpillars, maggots, or various other forms of larvae that feed and grow through a series of molts. A largely nonmotile pupa is produced at the last larval molt. A cocoon of silk may or may not be formed by the larva when it is ready to form the pupa, varying with the kind of insect. Finally, transformation to the adult occurs within the pupa, the shell of which is broken by the emergence of the adult.
An intermediate kind of change or metamorphosis occurs in certain aquatic insects, such as mayflies. The young stages, called nymphs or naiads, are quite different from the adults that do not live in water, and the transformation includes an active but nonfeeding subadult stage (subimago). In an evolutionary sense, the adaptation to complete metamorphosis was perhaps the single greatest achievement by insects. It enabled them to exploit a vast range of habitats by allowing adults and larvae to occupy and specialize in different niches. Complete metamorphosis allowed more versatile development of a resting stage, in which all growth and development can be stopped (diapause). This resting stage enables insects to synchronize activities to favorable seasons and to enhance survival during unfavorable times, such as the long dry season in California, by remaining dormant. Diapause may occur in the egg, larva, pupa, or adult, varying with the species. Many insects can even wait two or more years to complete the life cycle if seasonal conditions are highly unfavorable or uncertain, as in desert habitats.
Breathing and Circulation
Insects and related animals, such as sowbugs, spiders, and lobsters (Arthropods), have an exterior shell or skeleton within which the blood (hemolymph) freely circulates (open circulation). In insects the blood is moved primarily by the action of a tubular heart located in the upper part of the body cavity, opening just behind the brain. Blood is pumped forward to the head area, from which it circulates to the organs and into the appendages before reentering the posterior end of the heart.
In the majority of insects, air is taken in through holes in the body wall (spiracles). These are located along the sides of the body, usually one pair to each segment or fewer where segments have merged. Tubes (tracheae) lead from the spiracles throughout the body cavity. These branch through the organs and appendages, branching into finer and finer tubes (tracheoles). Oxygen passes from the tracheoles directly into the body, and carbon dioxide diffuses in the reverse direction. Most respiration is via passive diffusion, but limited, active pumping of air is known for some insects.
Some aquatic insects breathe in the usual manner, by periodically coming to the surface to collect a bubble of air. In many aquatic forms, however, breathing occurs through the general body surface, special organs, or gills. Therefore, some of these forms can spend their whole lives beneath the surface of the water. Insect gills are thin-walled out-growths located along the sides of the thorax, abdominal segments, at the tail end, or on some combination of these body regions. Oxygen diffuses directly from the water through the gill walls, which are well supplied with tracheae and tracheoles. Tracheal gills are present in immature stages of mayflies, dragonflies, damselflies, stoneflies, caddisflies, alderflies, and many aquatic two-winged flies.
Feeding
Insects use many methods to feed. The kind of mouthparts and the mode of feeding are generally correlated with major groups or orders of insects. Thus grasshoppers and related insects have jaws or mandibles adapted for biting and chewing, as do beetles, wasps, bees, and most other insects. By powerful musculature, the horizontally opposing mandibles are capable of biting through solid food substances, which may be as tough as hardwood. In other insects, such as aphids, leafhoppers, true bugs, and some flies, the mouthparts are formed into a tubular beak that is stabbed into the food and juices are sucked up using pumping action. Butterflies and moths have the mouthparts modified into a long, coiled tube that is inserted into food sources such as nectar in flowers, and this is taken up by a pumping action. In some insects, enzymes are ejected from salivary glands to liquefy food, such as dried honeydew, before it is sucked up. In other cases, as in mosquitoes and fleas, salivary fluid is injected that prevents coagulation of vertebrate blood that is then ingested. Many kinds of flies are adapted to feed on blood, and they have piercing and sucking mouthparts, while other flies take up their food via a proboscis with a sponge-like tip.
Most insects are harmless to humans from a medical or health standpoint. However, lice, fleas, bedbugs, and a few other true bugs as well as mosquitoes and certain other flies are familiar for their bites. Some bugs and flies, normally predaceous on other insects, can inflict a painful bite if prompted, but none of these injects venom comparable to that of a black widow spider. But certain diseases are transmitted by insects, especially in tropical regions, commonly by biting and blood-feeding insects. In California these diseases include plague, transmitted by fleas from rodents; encephalitis and West Nile virus infecting birds, transmitted by mosquitoes; and malaria, carried by mosquitoes. None of these is epidemic today in California, although some cases of West Nile virus, encephalitis, and plague are recorded each year. Other mosquito-borne diseases not known in California presently, such as Chikungunya or Zika virus, have entered the United States and in time may be found in the state.
Stinging
Few insects are capable of stinging, but often the term sting
is misused to describe insect bites. The true stinging apparatus is a modified ovipositor in female ants, wasps, and bees. No other insects sting, but many non-stinging insects mimic those that do and thereby gain protection from potential predators that are fooled. In contrast to insect bites, the sting is accompanied by the injection of toxins, a mixture of complex proteins and enzymes that act on the tissues of the victim, and in humans and other mammals this often causes the release of histamines. In humans, depending on individual sensitivity, the effects may be severe. Many kinds of wasps and bees are capable of stinging if provoked, but the behavior has its most damaging effect in social species: ants, yellowjackets, bumble bees, and the Honey Bee. When provoked, the workers rush out in great numbers to attack intruders, activated by alarm chemicals given off by their sisters. Some ants both sting and bite. In the Honey Bee worker the sting stylet is equipped with barbs so that it fixes in place and the entire sting apparatus pulls out of the bee, which kills her. Worker bees are expendable for the protection of the colony as a whole.
Distribution and Diversity of the California Insect Fauna
California’s size, long span of latitude, and diverse topographic features set the stage for tremendous biological diversity. The second largest of the 48 contiguous states, comprising an area about equal to the New England states, Pennsylvania, and New York combined, California by size alone would be expected to have large numbers of plant and animal species. In addition, several geographic and climatic zones are created by topography, dominated by two mountain systems. These ranges parallel the coast and serve to modify the ocean’s influence. Elevations extend from above 4,400 m in the Cascade Range and the Sierra Nevada to below sea level in the Imperial and Death Valleys. Average annual rainfall varies from more than 270 cm in Del Norte County to less than 5 cm in parts of the deserts. In most of the state, nearly all the precipitation falls between October and May. Coastal areas often have 365 frost-free days per year, while there are fewer than 100 at high elevations. Fog is also an important climatic influence, particularly along the coast, where it is regular during the summer months, and ground fog may be an important winter influence in the interior valleys.
Map 1. California counties.
Topography
Two major mountain chains compose the state’s most prominent topographical features: the Coast Ranges (including North Coast, Diablo, and Santa Lucia) and the inland Sierra Nevada, which are joined in the north by the southern end of the Cascade Range and in the south by the Transverse Ranges. The Sierra Nevada is the dominant feature; it consists of an immense granitic uplift more than 600 km long, extending from Plumas County to Kern County. In general, its east side rises abruptly from 1,500 to over 4,000 m defining the Great Basin to the east and descends gradually on the western slopes via a tipped plateau, divided by a series of deep canyons carved by the west-flowing rivers draining extensive snowpack. The Coast Ranges—subdivided into outer, marine-influenced, and inner, hotter, drier ranges—are lower but reach elevations above 2,500 m in the north. The Transverse and Peninsular Ranges also reach elevations of 2,500 m and 3,000 m and, like the others ranges, serve to block the ocean’s influence, creating a rain shadow effect resulting in arid interior regions.
Geographical Distribution
Many methods have been developed for describing and analyzing the distribution of animal species. These include defining geographical divisions, using vegetation types, ecoregions, and faunal provinces. None perfectly reflects the patterns of all species nor can any single system satisfy all biologists.
Botanists have classified the flora of California into natural plant communities or alliances. Most of these have a climatic basis and have been shaped by relatively recent events. Many plant alliances are highly influenced by soil type, hydrology, and fire regimes. An alliance is defined by the associated composition of plant species and is considered an emergent natural community. These communities vary in their distinctiveness and the complexity of their distributions. Based on A Manual of California Vegetation (Sawyer et al. 2009), there are now nearly 500 alliances so defined. These are organized into Woodland and Forest Alliances and Stands, Shrubland Alliances and Stands, and Herbaceous Alliances. This organization is a wonderful tool for botanists and land managers with a focus on plants but is difficult to apply to insects. For our purposes, we retain Munz and Keck’s (1959) 11 vegetation types, which generally are more useful in a qualitative discussion of insect occurrences and as a predictor of insect distributions in California. A great many insect species, especially plant-feeding forms, are restricted to one of the vegetation types: (1) Coastal Strand, (2) Salt Marsh, (3) Freshwater Marsh, (4) Scrub, (5) Coniferous Forest, (6) Mixed Evergreen Forest, (7) Woodland Savannah, (8) Chaparral, (9) Grassland, (10) Alpine Fell-fields, and (11) Desert Woodland. The California Native Plant Society provides an online tool for easy conversion between Munz Communities and California Vegetation Alliances.
Map 2. Major ranges and geographic features of California.
Because most insect species are more widely distributed than any given geographic feature or plant community, larger ecoregions provide convenient categories for distribution description and analysis. Perhaps the best approach to insect distributions in California is one in which faunal provinces are proposed, based on a combination of topographical features, ecoregions, and ecological or vegetation types. Many attempts have been made by biologists to define useful biotic provinces, but none has unanimous acceptance, primarily because various plants and animals differ in adherence to one or another of the criteria used to create the provinces. The ecoregions we present approximate what we see as optimal for insects (map 3). They are close to the regional terminology commonly used in scientific literature and are recognized by a wide array of biologists working in California. We have modified this based on our own collecting experience, data from the Essig Museum of Entomology, University of California at Berkeley, data from the Bulletin of the California Insect Survey, information about insect distributions from many colleagues, and reports from online resources such as BugGuide and iNaturalist.
Six provinces are defined for the entomofauna (entomological fauna), each including several plant community types and often multiple major geographic features (map 2). Perhaps half the state’s insect species are limited to one or a portion of one of these provinces, including the majority of plant-feeding types. Many species, including general feeders such as scavengers and predators, are more widespread, though many flightless species can be very narrowly distributed. The diversity of insects makes exceptions to any rule a regular occurrence. Although parasitoid insects often are specific to a host species or a particular habitat, others are less restricted and can be widely distributed. There are also many plant-feeding species that either feed on a wide variety of plants (polyphagous) or are restricted to one plant family or genus but use representatives that grow in diverse ecological situations.
The provinces presented here are intended as a tool for the insect enthusiast, observer, and collector to help them plan travels so they may more fully experience California’s insect diversity. Given that insects may violate any one system of areas, we take a mixed approach in describing their distributions and may refer to these provinces, the ecoregions, or even counties (maps 1–3) in describing the ranges for the insects. It should not overly surprise readers if in their explorations, they discover a species outside the range we have estimated for it. The entomofaunal provinces and their ecoregions that we use are as follows:
Sierran Province
The Sierran Province is the largest entomofaunal province, and it includes most of the state’s mountainous area. It includes many vegetation types and covers numerous topological features. There are many insect species or groups of closely related species that span the entire province. Some insects may be restricted to one or more of the ecoregions included in the province as described below.
SLOPES AND FOOTHILLS OF THE EASTERN CASCADES AND THE MODOC PLATEAU. Receiving much less rain than the adjacent high North Coast Ranges, this region has a more central-north continental flora and fauna. There are many buttes, cones, and plateaus of volcanic origin in the region, dotted with open conifer forests, scrub, and grasslands.
KLAMATH MOUNTAINS AND HIGH NORTH COAST RANGES. This region is irregularly bound on its western flank by the coastal fog belt
(see Coastal
below), extends from further north south into California, and is the southern extent of many insect groups that reach their greatest diversity in the Pacific Northwest. The area is thought to have been largely unglaciated during the Pleistocene and so has served as a refugium for northern species. It has a relatively mild and humid climate, though not as wet as the Coastal and North Coast Ranges.
NORTH SIERRA AND CASCADE RANGES. This is a disjunct portion of the larger Cascade ecoregion that extends from northern California through Oregon to Washington. The insect fauna blends northern elements and central Sierran elements. Some peaks reach over 4,000 m with rocky alpine and subalpine habitat on the slopes. Much of the lower elevations are moist, rich conifer forest, an area that has been heavily used for timber production. Many of the insects are shared with the Central Range.
CENTRAL RANGE. Traditionally this area is referred to as the Sierra Nevada. Containing most of the coniferous forests of the state and including a range from 1,000 m to over 4,000 m elevation, this region is probably the most diverse in habitat types and the richest province in insect species. Owing to its diversity, the Sierra Nevada has a high proportion of species that range into adjacent ecoregions or provinces, such as the Sierra Nevada foothills and the Coast Ranges. Nevertheless, there are vast numbers of insect species found only in this province.
WESTERN FOOTHILLS. This narrow, north-south region is characterized by Blue Oak and Foothill Pine woodlands and chaparral. It is on the western face of the Sierra Nevada from roughly 150 m to 1,000 m elevation. It shares a considerable number of species with the Sierra Nevada region above and the Central California Valley below but has endemics and often unique assemblages of species.
TRANSVERSE AND PENINSULAR RANGES. The region, diverse in vegetation and its associated insects, includes large areas of fire-prone chaparral and oak woodlands. At higher elevations summers are cooler and precipitation is greater than in adjacent ecoregions, resulting in many insect species that are shared with the Sierra Nevada, extending north but reaching their southernmost extent here. This is especially true in areas of extensive and diverse coniferous woodlands. These southern mountains are an ecoregion boundary with elements of the Mojave Basin, the Sierra Nevada, and southern California regions mixing or closely adjacent.
Map 3. Entomofaunal provinces and their ecoregions.
Coastal and North Coast Ranges Province
This province is dominated by the marine influence that results in summers characterized by fog and cool breezes at the coast. The marine effect diminishes quickly going inland, resulting in hotter summers and colder winters. A fog belt zone that extends from the coast to approximately 50 km inland is an area remarkably distinct from the drier inland areas for both plants and insects. The fog is vital to the ecoregion. For example, the Coastal Redwoods can get more than half of the water they need from fog, critical during the summer drought period. Winter rainfall is the highest in the state and can be nearly 300 cm, including significant snow accumulation at higher elevations.
COASTAL. The coastal ecoregion includes coastal strand and coastal plains dominated by grasslands and coastal terrace prairies, dunes, saltmarshes, and scrublands. In the north, lowland areas near the coast are dominated by Coastal Redwood and Douglas Fir–Tan Oak forests. The southern coasts and lower western-facing foothills are clothed in oak, pine, and chaparral.
NORTH COAST RANGES. This ecoregion is dominated by a series of ranges that parallel the coast and become successively higher elevation going inland. Characterized by plants and animals with northern affinities and including parts of the coastal strand, coastal scrub, and northern coastal coniferous forest, this ecoregion has a high proportion of insects that range along the coast from Vancouver Island, Canada, or further north. There are only a few species known strictly from California (endemic) in this area.
Central Valley Province
Much of this province has been converted to agriculture and oil and gas extraction, but there are still some remnant grasslands, marshes, vernal pools, riparian woodlands, alkali sink vegetation habitats, and stands of Valley Oak. Toward the southern end, this area shares an appreciable number of its insects with the Mojave Desert, especially those of the western San Joaquin Valley, which has sandy areas harboring desert plants. Many other insects occur widely here and in the western foothills and the central coastal western mountains and foothills.
Californian Province
This, the second-largest province, extends over much of the length of the state. It has a distinctly Mediterranean-type climate and a larger proportion of species endemic to California than any other province. This area is also diverse in habitats, soils, and microclimates.
CENTRAL COASTAL WESTERN MOUNTAINS AND FOOTHILLS. This region contains the central coastal strand and coastal scrub as well as the chaparral, foothill woodland, and coniferous forests of the central and southern ranges. All of these are relatively arid compared to their northern counterparts. Although most insects range northward into the Coastal Ranges or east in the Sierra Nevada, a large number occur only in this region or are shared with the adjacent Southern California/northern Baja coast. A central geographic feature is the Diablo Range, extended from the northeast at the San Joaquin River to the southwest at the Salinas River, bordered on the east by the San Joaquin Valley. This range is drier, hotter, and shares more with the Central Valley than its parallel counterpart to the west, the Santa Lucia Range that defines the Big Sur coast.
The Channel Islands have been treated by some as a distinct province, but the islands’ insects generally are those of the mainland. The insects are not well inventoried, but it appears that most of those of the northern island group, especially Santa Cruz Island, are species also found in the central coastal western mountains and foothills region, with few endemic species. By contrast, the southern islands, especially the more distant ones, have higher numbers of endemics and a greater affinity with the southern part of the southern California/northern Baja coast and the desert provinces.
SOUTHERN COASTAL MOUNTAINS AND FOOTHILLS, AND NORTHERN BAJA COAST. This is a region with coastal and alluvial plains and low hills, extending south into Baja California. Though the vast majority of the native habitat has been converted for human use, the remaining grasslands, coastal sage scrub, scrub oak, and mountain-mahogany habitats include endemic plants and insects. The southern Channel Islands appear to share much of their insect fauna with this region.
Great Basin Province
California only includes the far western fringe of the Great Basin. The bulk of the ecosystem extends over 1,200 km east from California ending at the Rocky Mountains. Generally the relatively dry, cold climate of the province supports mainly steppe shrub and grasses at low and medium elevations and conifer and aspen trees at higher elevations.
NORTHERN BASIN AND RANGE. This area represents the western edge of a vast sea of sagebrush scrub covering areas to the east and north of California. It is rather uniform in character, rich in species, and relatively distinct from other parts of the state’s fauna. It contains almost no insects endemic to California, as the majority of the area is in eastern Oregon and southern Idaho. It is cooler and wetter than the Central Basin and range and so has a much more northern faunal influence.
CENTRAL BASIN AND RANGE. This region is the western edge of the Great Basin region. Aside from the overlapping fauna with the Northern Basin and range, it is highly distinct from the rest of California. It is significantly warmer, especially during summer, and somewhat drier than the Northern Basin and range. Many species that are widespread from California to Utah are at the western edge of their distribution here.
Desert Province
This province is very distinct within California but harbors few endemics. It is characterized by low and rather unpredictable rainfall. The higher elevations receive regular snowfall and relatively longer winters, while the lower elevations may remain warm year-round and very rarely experience freezing temperatures.
MOJAVE BASIN AND RANGE. This region has broad basins, alkali flats, and scattered, rocky mountains. The vast majority of species that are restricted to this province in California also range into Arizona, Nevada, and beyond. Within California the overall similarity in insect species with the Colorado Basin and range is very high, although there is a merging of Mojave, Sierran, and Central Valley faunas near the Tehachapi Mountains and Transverse Ranges.
COLORADO BASIN AND RANGE. Though similar in its insect fauna to the Mojave, this low desert region is notably hotter, with large areas of Giant Saguaro Cactus and a mix of palo verde and smaller cactus species, compared to the typical vegetation in the Mojave, which is largely Creosote Bush. This area also includes the largest areas in the state of wind-blown (aeolian) sand deserts with active dunes and the longest stretch of Colorado River shoreline. The sparse precipitation that might fall in this region is almost equally divided between winter rain systems and the occasional late summer monsoon that may stray west from Arizona. Both of these sources of precipitation can fail to materialize, sometimes for years.
Diversity
Summer visitors from the eastern United States, especially if their travels are restricted to lowland areas, around the cities, and major north-south highways, often remark on the dryness of the California countryside. Insect collectors from places like Minnesota or Illinois, arriving here in June, when the collecting season is just getting into full swing there, are dismayed to find that it is about finished in lowland California. Unless they obtain local advice or plan to work in the mountains, these visitors are likely to find summer collecting in California a bleak prospect; and they may justifiably find it hard to believe that we have a larger number of insect species than nearly any other state.
The mild climate with a long dry season is a key to the hidden diversity. Prolonged drought imposes a strong seasonal partitioning on plants and animals. In California this is superimposed on the topographical diversity, creating a complex mosaic of geographical, ecological, and seasonal niches to which insects have adapted. Northern, higher-elevation, and interior regions of North America have a short growing season, with the vast majority of the insects active during summer months. In most of California, by contrast, the growing season for annual plants takes place mainly during winter and spring. The insects feeding on annuals and using their pollen, as well as associated parasitic insects, must complete their activity early, often ahead of the growing and flowering seasons of perennial plants.
For example, small moths are active in January and February in southern California and along the immediate coast northward. They are day-fliers and are dark-colored to take advantage of the sun’s warming during a season when temperatures at night are too cold for activity. This early start enables their larvae to complete feeding before the annual plants, on which they specialize, dry out in late March or April. Comparable adaptations occur in large numbers of other insects. Even species associated with broad-leafed shrubs and trees often complete their activity early. Leafing out generally occurs at the end of the rainy season, in April and May, and the leaves harden, becoming more resistant, by summertime. Many other insects are active in fall, such as those associated with fall-blooming composite shrubs. Many fall-fliers feed as larvae in spring, having overwintered in the egg stage.
Therefore, to study the insects of California, all seasons have to be considered. At lower elevations there are many spring-active species from January to April, but there are summer species in marshes, river habitats, and in association with perennial plants. Elsewhere in the state insect activity peaks in the foothills by May, at intermediate elevations in June, and in the high Sierra in July or August. By the time regular frosts occur at timberline, fall-active species are in full swing at low elevations. Even during the most dormant period (mid-November