Wasp Wednesay: Hemipepsis ustulata

The term “tarantula hawk” applies to more than one species of large wasp. It even applies to more than one genus. Here in the United States, the genera Pepsis and Hemipepsis are the only tarantula hawks, and the largest of our spider wasps in the family Pompilidae. Hemipepsis ustulata is a common species across much of the western U.S., one I have encountered in both Arizona and Colorado.

It is not easy to separate Hemipepsis from Pepsis, but I find that Hemipepsis are matte black in color, not the iridescent blue-black that their relatives are. Hemipepsis also tends to fly earlier in the season than Pepsis, especially in the southwest, but both genera can be found together in the fall, Hemipepsis being in the second generation in autumn. Wing venation is apparently the only sure way to tell the two apart, but most folks understandably don’t want to get that close to such a large, stinging insect to find out which is which.

Tarantula hawks in general have interesting behaviors, especially the males. Dr. John Alcock has studied in-depth the territorial behavior of male Hemipepsis ustulata in the Superstition Mountains near Phoenix, Arizona. They are among the first insects seen in spring, but as the season wears on they become early risers, taking advantage of the brief window of time when Sonoran Desert temperatures are not too cool, but not incinerating, either. They are looking for prominent outposts, often Palo Verde trees atop hills.

Once a male wasp claims a lookout tree, it vigorously defends it from competing males. Most interactions consist of the resident male flying off his perch in a brief foray to chase away the intruder. There is usually only feeble resistance, if any, from the interloper. Males that have been displaced from their own territories, however, are more likely to try and displace another male. This takes the form of long, ascending flights in which the wasps spiral around each other as they climb to heights of thirty feet or more. Sometimes they escalate to altitudes where they can no longer be observed without binoculars.

These aerial duels are contests of both endurance and speed. The faster and fitter male is thus the one more likely to win.

Female wasps cruising past an occupied tree elicit an entirely different response. The resident male gives chase and, if he successfully reaches her, attempts to couple with her in the air and descend to the ground. There, they mate briefly if she is receptive. The male then returns to his perch, which he hopes has not been claimed by another male while he was um, otherwise engaged.

This form of territoriality is called “landmark defense,” and it is the strategy of choice in situations where defense of a resource used by females is impractical or impossible. While blooming palo verde trees might seem to be a nectar source for female tarantula hawks (and they are, for Pepsis chrysothemis), females of Hemipepsis ustulata seem to prefer the flowers of creosote bush, which has a wide and scattered distribution in the landscape.

Once mated, a female tarantula hawk goes about the business of finding occupied tarantula burrows and baiting the spider into battle aboveground. These burrows are also widely scattered. So, male wasps can’t stake out a tarantula “colony” because there is no such thing, at least not for spiders the size needed by the female wasp.

Some of the hunting activities of these wasps may take place at night, or at least at dusk, for I have found females in southeast Arizona coming to blacklights at night. I have also found females feeding on oozing sap of Desert Broom (Baccharis sarothroides). Here in Colorado Springs I have seen both genders at a blooming saltcedar tree (Tamarix sp.), though the female simply circled the tree and flew off again.

Hemipepsis ustulata ranges from southern California east through Nevada to Texas, Oklahoma, and Kansas. It would be well worth it to accumulate more records of this species. More county records are certainly possible, and perhaps state records, too.

Sources: Alcock, John. 1984. “Ridgetop Rendezvous,” Natural History 93: 42-47.
Evans, Howard E. 1997. “Spider Wasps of Colorado (Hymenoptera, Pompilidae): An Annotated Checklist,” Great Basin Naturalist 57(3): 189-197.

Spider Sunday: Phidippus octopunctatus

If the spider world ever had a beauty contest, the winner would likely be a jumping spider in the family Salticidae. Some are clad in the equivalent of clown suits, others in camo, but many seem to have a fashion sense that would be the envy of any human clothing designer. Such is the case with males of the species Phidippus octopunctatus.

The species name might suggest that it would have eight spots (octo=eight, punctatus=punctures or spots), but this is not so. The male, a sizeable, densely hairy spider averaging 9.35 millimeters in body length, is black underneath, with black legs, and a beautiful silvery gray above. Females, slightly larger in size at 10.19 millimeters, are uniformly gray or beige. The spiderlings may have a vaguely striped pattern on the abdomen, but otherwise look similar to the adults.

This color scheme may benefit the spider, as some species of velvet ants are very similar. Velvet ants are solitary wasps, the females of which are wingless, and capable of an excruciating sting in self-defense. Potential predators quickly learn to steer clear of velvet ants; and other arthropods that mimic velvet ants would also be avoided.

Velvet ants and Phidippus octopunctatus also favor the same kind of habitat: prairies, grasslands, deserts, and open fields. The spider ranges over most of the western U.S., from southeast Washington to California and east to Iowa, Missouri, and Texas. It also occurs in northern Mexico.

This is one wary animal, and getting images of wild individuals is a real challenge. They see you coming from a mile away (well, ok, at least a couple of yards), and dodge behind a yucca blade or quickly descend into undergrowth. Catching one out in the open, as I did in Stratton Open Space in Colorado Springs on June 1, 2012, is no guarantee of a good shot, either. They make a run for it as soon as they see you.

There are some truly spectacular images of this species by Mark Chappell of the University of California, Riverside. Note that the jaws are not metallic green or red as they are in other Phidippus species. Males may be territorial, as evidenced by the intimidating display shown in one of Mark’s images.

I encourage my readers to look for this species, as its geographic distribution is rather sketchy. No records appear to exist for Oregon, Idaho, or Wyoming for example. Adult specimens are usually found in summer, but their longevity is unknown. Do they live longer than one year? What does their courtship ritual look like? Your images, videos, observations, and notes could greatly illuminate our view of this spider.

Sources: Edwards, G.B. 2004. “Revision of the Jumping Spiders of the Genus Phidippus (Araneae: Salticidae),” Occasional Papers of the Florida State Collection of Arthropods 11:1-156.
Metzner, Heiko. 2012. Jumping Spiders (Arachnida: Araneae: Salticidae) of the World.
Proszynski, Jerzy. 2003. Salticidae (Aranae) of the World. Museum and Institute of Zoology, Polish Academy of Sciences.

Fly Day Friday: Greater Bee Fly

Spring is just around the corner here in the northern hemisphere, and one of the first insects you are likely to see is a buzzing fuzzy ball looking for nectar and moisture. That would be the Greater Bee Fly, Bombylius major. It is perhaps the most familiar and abundant member of the family Bombyliidae found in North America, Europe, the Middle East, and temperate Asia.

People unfamiliar with bee flies might interpret the long beak as a device for sucking blood, and identify the fly as some kind of mutant, hairy mosquito. Nothing could be farther from the truth. Those long mouthparts allow the fly to reach nectar deep inside some flowers, even while the fly may be hovering in front of the blossom.

That hovering behavior is yet another hallmark of bee flies in general, but this species especially. The territorial males are so accomplished that I was able to take images of one hovering about 2-3 feet off the ground at the Tucson Botanical Gardens in Arizona on March 24, 2010.

Also known as the “Large Bee Fly,” Bombylius major is not exceptionally big. Adults measure 12-18 millimeters, with a wingspan of up to 25 millimeters. Many other bee flies are larger. Size varies according to the degree of nutrition consumed in the larval stage.

Despite the familiarity of this species, surprisingly little is known about its life cycle. It is definitely parasitic in the larval stage, and so far the only known hosts are solitary bees in the genera Andrena (“mining bees”), Colletes (“plasterer bees”), and Halictus (“sweat bees”). This fits with the presence of the adult bee flies in the early spring, as that is also when female mining bees are excavating burrows and provisioning the underground cells with pollen and nectar.

© Eric R. Eaton

The female fly locates an open nest burrow of its host and supposedly hovers over it, lobbing eggs down the tunnel with flicks of her abdomen. The larva that hatches from each egg then actively seeks out an individual cell with a larval bee. The fly maggot then waits patiently while the host eats the pollen and nectar ball, growing large and plump just before it pupates. Then the maggot makes its move, attaching itself to the exterior of the bee larva. There it feeds as an external parasite, eventually killing its victim.

The mature fly larva then pupates, usually spending the winter in that stage. Scientists in Sweden have noted that pupae occasionally pass two winters before the adult fly emerges (McAlister, 2013). The pupa is armed with hooks, spines, and stiff bristles (setae) that it uses to work its way through the soil plug closing the bee’s burrow. Upon reaching the surface, the adult fly breaks out of the pupal exoskeleton, leaving it behind.

Look for these flies in yards, gardens, forest edges, sunny spots in woodlands, and similar situations. This species, which also goes by the names “Dark-edged Bee Fly” and “Black-tailed Bee Fly,” is flying mostly between March and June, but is especially common in April and May. They are at least potentially important pollinators of a number of wildflowers such as Gilia.

Sources: Cole, Frank R. 1969. The Flies of Western North America. Berkeley: University of California Press. 693 pp.
Hull, Frank M. 1973. Bee Flies of the World. Washington, DC: Smithsonian Institution Press. 687 pp.
McAlister, Erica. 2013. “Bombylius major (Large Bee Fly),” Nature Online, Natural History Museum (UK).
Talibart, Rachael. 2012. “Bee Fly,” Focused Moments.

True Bug Tuesday: Brown Marmorated Stink Bug

Ok, ok, I confess. I watch that awful Animal Planet show Infested! What is often more appalling than the crises faced by the people showcased in the program are the rampant errors and hyperbole provided by many of the “experts.” One recent episode, however, was probably not overly exaggerated. It featured a family whose rural Pennsylvania home was overrun with Brown Marmorated Stink Bugs, Hyalomorpha halys, that were seeking winter shelter.

I have written about this invasive species previously, in a feature on ”Common Indoor Insects of Autumn”, having never seen one in person. That changed last year when my wife and I visited Cape May, New Jersey. Many structures, from buildings to Port-O-Lets, were being investigated by the bugs as potential winter hang-outs. The insects were also common on foliage and vehicles.

Since my first article, things have gotten even worse. H. halys is now found in most states east of the Mississippi River, plus the Pacific Coast states, and now Utah. Furthermore, it has elevated its status to that of a bonafide agricultural pest. In fact, it is essentially number one on the U.S. Department of Agriculture’s “most wanted” list.

The Brown Marmorated Stink Bug is what is called a “generalist” feeder, meaning that there are a wide variety of plants on its menu. Most insects are “host-specific,” unable to eat plants outside of one genus or family. The Monarch butterfly is a good example of a host-specific insect. The caterpillars can only eat the foliage of milkweed and closely-related plants. Contrast this picky diet with that of H. halys. Over 300 species of plants are palatable to it in the nymph and adult stages.

This versatility in host plants translates to a potent economic impact. The bug accounted for $37 million in losses to apple-growers alone in 2010. Other crops adversely affected include raspberries and blackberries; and organic farmers reported losses of beans, peppers, and tomatoes. The cosmetic damage alone can render some produce unsalable.

Like all true bugs, stink bugs feed on plant sap and juices through beak-like piercing-sucking mouthparts. Their sipping and sucking can cave-in corn kernels, wither fruits, and leave unsightly stains behind.

Adult male Brown Marmorated Stink Bugs also emit an “aggregation pheromone,” a kind of aromatic chemical cocktail that attracts other males, females, and nymphs to food sources. So, as if a single bug isn’t bad enough, he recruits friends and family. Scientists may be getting closer to using that pheromone as a weapon against the bug, by drawing them into traps, for example.

Back to that episode of Infested!. It had a happy ending. Initially demoralized by the overwhelming number of bugs holding them prisoner indoors and eventually infiltrating their home, the family turned the problem into profit. The father devised a light trap to attract and kill the bugs, and is now selling his invention to others.

Sources: Gibson, Caitlin. 2013. “Stink bugs could mount a comeback this spring,” The Washington Post, January 5, 2013.
Murray, Todd, et. Al. 2012. Pest Watch: Brown Marmorated Stink Bug. Washington State University Extension Fact Sheet FS079E. 5 pp..