Bug Eric

A good many people mistake me for an expert who knows everything about every insect known to man, but I am not. Thankfully, there are entomologists like Doug Yanega who do seem to know everything, but he would be the first to deny that claim as well. Still, I have learned more from him than I can possibly recount. Case in point a wasp that had me scratching my head over the weekend.

This all started out innocently enough. I was down at Chico Basin Ranch, a sprawling 88,000 acre cattle ranch that straddles the El Paso and Pueblo County line on the high plains, looking for grasshoppers with several other members of the Mile High Bug Club and the general public. At our first stop out on the heavily-grazed shortgrass prairie, one of the first insects that got my attention was a small, maybe 20 millimeter-long, slender black-and-red wasp that was running erratically between patches of grass.

I had it pegged as either a thread-waisted wasp in the family Sphecidae, or a spider wasp in the family Pompilidae, both of which behave in this manner as they search for potential prey. I did not have the camera set for speeding Hymenoptera, so the images are a bit blurry. Now I am wishing I had spent more time with this creature, but hindsight is twenty-twenty. I do not recall the wasp ever flying, but I figured a close approach might send it fleeing permanently.

Back at home, reviewing the magnified images on my computer, I quickly decided I had no clue at all as to what I was looking at. It seemed to be a fusion of the two potential suspects I had surmised initially. So, off to the "Hymenopterists Forum" on Facebook I went. Posting the images there got me several "likes," but no one ventured an identification. Enter Doug Yanega, a good friend and colleague from the University of California at Riverside. He is always willing to help others online and in person, and the university's collection is so well organized that he can use it as a reference for cases like mine.

"I just recalled the other name I was thinking of: Pterombrus rufiventris (now in Thynnidae). I can't find any photos of it online, but I caught one in Kansas once and it had me stumped for a while," wrote Doug. Well, nice to know I'm not the only one who has been baffled by this species. Doug went on to add "Just checked our collection, this is Pterombrus rufiventris, and it attacks cicindeline larvae. Very rare but widely distributed. No photos in BugGuide."

It is no wonder that I did not recognize it, because the most common thynnid wasps are in the genus Myzinum, and they look nothing like this. See my blog post on those here.

Cicindelines are known commonly as tiger beetles, colorful and active predators in their own right. The larval stage typically lives in a vertical burrow with a diameter just barely large enough to accommodate the grub. The larva has a flattened head that is held flush with the top of the burrow, the better to see, lunge after, and seize any unsuspecting insect that happens by. The victim is then dragged into the burrow to be consumed. A wasp has to have a lot of bravery to take on one of these voracious beasts, armed as they are with large and powerful jaws. True, the wasp does have her stinger, and I can only imagine how deftly she must wield it to be successful.

According to field observations by others, the wasp crawls down the burrow of the tiger beetle larva and stings it repeatedly under the head or thorax, before depositing an egg on the grub's abdomen. The mother wasp then plugs the burrow with a solid, compacted layer of soil, and then fills in the remainder of the burrow above the plug with loose soil particles. Her egg hatches in about 3 days, and the wasp grub that emerges grows by feeding on the tiger beetle larva for almost 9 days. The mature wasp larva then detaches from the now-deceased host and spins a cocoon in the burrow of the host. There it overwinters, emerging the following summer with the monsoon rains of July.

Indeed, this year Colorado has seen extraordinarily heavy precipitation from severe storms. Timing is everything, and I consider myself lucky to have crossed paths with this rare insect. These are perhaps the first images online of the species. Keep your eyes out for this, the western subspecies P. rufiventris hyalinatus, and the eastern subspecies P. r. rufiventris, from southern California to Texas, and on to Georgia and Virginia.

Sources: Knisley, C. Barry, Darren L. Reeves, and Gregory T. Stephens. 1989. "Behavior and Development of the Wasp Pterombrus rufiventris hyalinatus Krombein (Hymenoptera: Tiphiidae), a Parasite of Larval Tiger Beetles (Coleoptera: Cicindelidae)," Proc. Entomol. Soc. Wash. 91(2): pp. 179-184.
Krombein, Karl V., et al. 1979. Catalog of Hymenoptera in America North of Mexico Volume 2. Washington, DC: Smithsonian Institution Press. 1199-2209.

My last post here chronicled predation on termites by ants in the wake of swarming events in my neighborhood. Today I shall turn the tables and demonstrate that ants are not immune to predators themselves. Antlions and tiger beetles are among the few predatory insects that kill and eat ants. Ants can bite, and either sting, or spray formic acid to defend themselves. One cannot blame a potential predator for avoiding that kind of trauma when ants are not much more than an hors d' oeuvres anyway.

While looking for tiger beetles in Lake Pueblo State Park, Colorado on March 18, I was surprised to find the funnel trap of an antlion larva in the middle of a game trail. Usually, the pitfall traps of antlions are clustered, and situated in sheltered areas like beneath a rock overhang, at the base of a tree, or other location where rain seldom if ever reaches them. Since the only genus of antlions in the U.S. that makes such traps is Myrmeleon, I knew that had to be the critter lurking at the bottom of the pit.

Buried just beneath the dusty sand was a single, chubby larva, studded with spines on various parts of its body, and with menacing sickle-like jaws. Nearly blind, the insect relies on its sensitivity to vibration to detect potential trouble or potential prey. When an ant or other terrestrial insect blunders into the antlion's steep-walled trap, the larva becomes alert and proactive. It may use those jaws to fling sand onto its victim, hastening its descent to the bottom of the funnel. The predator then grabs its prey and injects it with enzymes that paralyze it and begin the digestive process.

Antlions go through complete metamorphosis, so the larva eventually constructs a cocoon of sand and silk in which it pupates. An adult antlion, more than making up for its youthful ugliness with its delicate wings and slender body, emerges from the pupa at a later date.

The fate of ants in the jaws of an antlion may seem morbid, but it is still better than what happens to ants caught by adult tiger beetles. After two consecutive days of unsuccessful searching for tiger beetles closer to home in Colorado Springs, I finally found at least three Blowout Tiger Beetles, Cicindela lengi, on the afternoon of March 23. I was witness to their ability to swiftly dispatch lone worker ants with their huge, toothy jaws.

Most tiger beetle species are agile daytime hunters that haunt sandy habitats like the sandhill bordering the vacant lot where I found these specimens. The insects run quickly, stop, then run again. They fly a short distance if spooked by a potential predator. Their eyesight is keen, vastly more sensitive to motion than a person; but they focus slowly. They literally outrun their eyesight when pursuing prey, and must stop to refocus before rejoining the chase. This herky-jerky hunting strategy is still effective, and few insects spotted by a tiger beetle will live to tell the tale.

Tiger beetles appear to have the speed and power to attack insects and other invertebrates at least as large as they are, but most of their victims are quite small. Ants seem to be near the limit of what they will take. They make short work of even the feisty Western Harvester Ants, Pogonomyrmex occidentalis, that are abundant in Colorado Springs. The jaws of the beetle quickly dismember the ant, leaving a trail of carnage around the beetle. The beetle's next victim may be a tiny, unidentifiable invertebrate it plucks from between sand grains.

Most tiger beetle enthusiasts are fond of remarking that they are glad tiger beetles do not get any larger in size than they do. Indeed, I would not be prowling around dunes and beaches if there were even raccoon-sized tiger beetles in the neighborhood. Since they are much smaller than that, I recommend going in search of them. Their beauty and behaviors are sure to capture your curiosity and sense of wonder.

I have decided to begin a new, recurring feature here called "ID Tips" that will be designed to help naturalists, amateur and student entomologists, and others solve common and basic problems in insect and spider identification. Our first installment will explain differences between ground beetles (family Carabidae) and darkling beetles (family Tenebrionidae). The two are easily confused, but generally straightforward once you know what to look for.

One glaring difference between carabids and tenebrionids is the structure of the antennae. In ground beetles, the segments of the antennae are usually longer than wide, giving the antenna the appearance of a near single filament. Darkling beetles have mostly bead-like segments, such that the antenna resembles one of those keychains that closes by pushing the filament between the beads into a clasp. This is not a foolproof character, but works enough of the time that it will help you make a quick determination.

Look also at the front of the head. Are the mandibles (jaws) exposed and directed forward? If so, then you have a ground beetle or another kind of predatory beetle. Conversely, if the mandibles are concealed beneath the clypeus ("upper lip" if you will), then it is likely your specimen is a darkling beetle or another beetle that feeds on vegetation or detritus.

Does your beetle move very rapidly by running? This is another characteristic of ground beetles. Many species are so fast that it is a real challenge to catch them for closer examination. Does your beetle lumber along slowly or only run fast when prodded? Chances are you have a darkling beetle then. Many darkling beetles rely on a very dense exoskeleton to repel attacks by predators, and consequently don't feel the need to flee in haste. Desert and prairie species may even have the wing covers fused to help limit water loss.

Does your beetle stand on its head when disturbed? This head-standing behavior is characteristic of the darkling beetle genus Eleodes, and some other closely-related genera. Both darkling beetles and ground beetles can have extremely effective chemical defenses that include pungent, permeating aromatic compounds released from abdominal glands, so smelling your beetle to make an identification is not only a potential exercise in futility, it can be highly unpleasant if not injury-inducing.

Habitat is not a good way to distinguish ground beetles from darkling beetles. Both can be found in a variety of habitats, and are especially abundant and diverse in aridland ecosystems.

Because both carabids and tenebrionids are well-defended insects, they are mimicked by a variety of unrelated insects. One prime example is the longhorned beetle genus Moneilema, which mimics Eleodes darkling beetles not only in appearance, but behavior. The longhorned beetles, which feed mostly at night, on cactus pads, move slowly and even stand on their heads like Eleodes. They have no chemical defense to back-up their warning posture, but the bluff works fine on all but the most desperate of insectivores.

Another complication is the relatively recent assimilation of two former beetle families into the Tenebrionidae, many of which do not resemble "classic" darkling beetles. These are the comb-clawed beetles (subfamily Alleculinae) and long-jointed beetles (Lagriinae).

In contrast, the "ironclad beetles" in the family Zopheridae were once members of the Tenebrionidae. They include beetles so well-armored that entomologists have extreme difficulty in pinning specimens that they collect.

No single character is probably reliable by itself, and it is recommended that one use a dichotomous key, in a technical book or online, to reach a firm conclusion on the identity of your beetle. It is also a great idea to invest in a good dissecting (binocular) microscope. Good luck!

Early spring along the Front Range of Colorado is deceptive. Few flowers are in bloom by mid-March, and there is little color to indicate that life has changed since winter's onset. Tiger beetles to the rescue! So far this spring, local bug-watchers have seen and photographed nine species of these exquisite animals.

Tiger beetles were once placed in their own family, Cicindelidae, but are now considered a subfamily (Cicindelinae) of the ground beetles, family Carabidae. Their taxonomic "demotion" has not diminished enthusiasm for these charismatic predators, a favorite of entomologists and increasingly popular among naturalists in general.

The common tiger beetles of the genus Cicindela prefer open, sandy habitats such as beaches, dunes, and barren paths through prairies and forests. Some are agile enough to negotiate obstacles on rocky shores and riverbanks, too. It is frequently a matter of luck finding them. Perfectly appropriate habitats may be devoid of tiger beetles, while other locations are chalk full.

Cicindela tiger beetles average 11-14 millimeters in body length. Most are brown with ornate ivory markings, but a few are metallic green or red, or both. Most are decorated with white hairs that help insulate them from the hot sun. They have large eyes, long legs, and enormous mandibles.

Most tiger beetles you see will be running away from you, but sit and watch and eventually they become accustomed to your presence and resume normal behavior, like hunting. Tiger beetles pursue small invertebrates, including ants. The beetles have excellent vision and quickly detect the movement of a potential meal. They run after it, but may stop before they reach their target. Tiger beetles are so fast they can actually outrun their ability to focus. So, they stop, re-focus, and dash off again. Once they overtake their prey, those menacing jaws quickly reduce the victim to shreds.

Another favorite activity of tiger beetles is making more tiger beetles. You will often see one beetle atop another. The one on top is the male. The pronotum (top of thorax) of the female of each species has notches and dents that will only accept the toothed mandibles of the corresponding male. This stops interbreeding with the wrong species, but allows the right male to "get a grip" on the object of his affection.

Competition for the girls is keen, and sometimes a male will be late to the party. The result can be a comedic "conga line" of stacked cicindelids.

Even in the relative cool spring and fall months, tiger beetles are in danger of overheating on the scorching sand. Consequently, they may seek shade under low-growing plants. They also use their long legs to elevate themselves high off the ground. Being on "tip-toe" makes them no less wary and agile.

The metallic nature of tiger beetles is structural, rather than the result of pigmentation. Layers in the exoskeleton reflect various wavelengths of light. Despite their colorful appearance, the beetles are still surprisingly cryptic. When disturbed, tiger beetles can fly, then alight facing the direction of the threat, reducing their profile. Sometimes, they hunker down in a depression in the sand, becoming even more inconspicuous. Ivory patterns on the elytra (wing covers) break up the outline of the beetle even more.

The tiger beetle species present as adults now are spring-fall species that spend the summer as larvae and pupae in tunnels in the soil. The larvae are ambush hunters that each live in a vertical shaft of their own making. They present their flat heads at the entrance to the burrow, flush with the opening. Any small invertebrate that passes by risks being seized by the larva.

The summer months see a different set of species that share the same habitat. So, visiting the same site at different times of the year can yield an entirely different fauna.

The species we have seen here on the plains and east slope of the Rocky Mountains this year include: Oblique-lined Tiger Beetle, Cicindela tranquebarica; Bronzed Tiger Beetle, Cicindela repanda; Twelve-spotted Tiger Beetle, Cicindela duodecimguttata; Western Tiger Beetle, Cicindela oregona; Green Claybank Tiger Beetle, Cicindela denverensis; Purple Tiger Beetle (aka "Cowpath Tiger Beetle"), Cicindela purpurea; Blowout Tiger Beetle, Cicindela lengi; Festive Tiger Beetle, Cicindela scutellaris; Splendid Tiger Beetle, Cicindela splendida. Each species can be highly variable in markings, with enough overlap with other species to make matters confusing to the novice observer. Pay attention to habitat, behavior, and size.

Mostly, simply enjoy watching these spirited insects as they go about their lives. At the least it is a rewarding diversion, but it can lead to new discoveries, too. Our understanding of even the distribution of tiger beetle species is poor; and because they are found in habitats vulnerable to human development, some species are threatened or endangered.

Sources: Acorn, John. 2001. Tiger Beetles of Alberta. Edmonton: University of Alberta Press. 120 pp.
Schmidt, Justin P. 2002. "Cicindelidae of Colorado," Colorado State University.

One of the few insects to have poked its head out while we still have the threat of snow here on the Front Range of Colorado is the Cow Path Tiger Beetle, Cicindela purpurea. Also known as the “Purple Tiger Beetle,” it seems to come in just about every color except purple. Whatever its wardrobe, it is a welcome sight and a challenging subject to stalk and photograph, whether here or elsewhere on the continent.

Tiger beetles in North America typically have one of two emergence patterns. Some have a two-generation spring/fall cycle whereby the adult beetles are present in those two seasons. Others have one generation seen only in summer. Many species also have specific habitat requirements, making them hard to find in the first place. Then there is the fact that if they aren’t moving, you have a hard time seeing them.

These beetles also earn their name: they are efficient predators of many other insects, even ants. They have reasonably keen vision and run swiftly, like diminutive cheetahs. They run so fast, in fact, that they can literally outrun their eyesight. When sprinting after a potential meal, they go blind, and must stop to re-focus. This run, stop, run behavior helps to identify them in the field. Get too close to one and it will fly, usually a short distance, land, and resume its darting gait.

Tiger beetle larvae are also predatory. Each lives in a (usually) vertical burrow just wide enough to accommodate the grub. A hump midway down its body, armed with hooks, anchors the larva against one wall. The overall appearance of the grub is an “S” shape. The flattened head of the larva is flush with the rim of its tunnel as it lies in wait for a hapless insect to blunder by. It then lunges with lightning speed, grabbing the victim in its jaws. When disturbed, a tiger beetle larva rapidly descends deep into its lair.

Adult Cow Path Tiger Beetles measure 12-16 millimeters and may be matte green, metallic green, bluish, black, or bronze-purple with green highlights. The species has been divided into named “races” based on these differences. Most have consistent ivory markings: a spot at the tip of each elytron (wing cover), and a mark that looks like an oblique tilde symbol (“~”). There may or may not be an additional spot near the edge of the elytron between the squiggle and the terminal spot.

It is not unusual to find two different color morphs to be mating, as shown here. They recognize each other by the dimples in the female’s thorax, which fit the teeth on the male’s jaws like a lock and key. Attempted mating by the male of another species would be futile, as his jaws would slip off her thorax.

Look for these lovely beetles in degraded prairie habitats, where there is sparse grass and plenty of bare patches of earth. They are not often found in large numbers, and while much of a given landscape may look to us to be hospitable to them, they can be sporadic at best.

The good news is that Cicindela purpurea is a very widespread species found over most of the northern three-fourths of the U.S., plus adjacent southern Canada. It is largely absent from the mid-Atlantic states, southeast, Texas, and coastal areas of the Pacific states. April, May, and September are the months this species is most abundant. Keep in mind that some years they might emerge earlier or later, depending on how mild the winter is.

Sources: Acorn, John. 2001. Tiger Beetles of Alberta: Killers on the Clay, Stalkers on the Sand. Edmonton: University of Alberta Press. 120 pp.
MacRae, Ted. 2011. “Monroe Canyon epilogue – Audubon’s tiger beetle,” Beetles in the Bush.
Anonymous. 2005. “Cow Path Tiger Beetle,” Tiger Beetles of Nebraska.