Wednesday, July 28, 2010

Wasp Wednesday: Prionyx thomae

Sometimes it is easier to identify a wasp by the prey it is carrying than by the wasp itself. Ned Harris and myself found this wasp at Madera Canyon’s White House Picnic Area last week. Ned noticed the grasshopper prey before I did. I was convinced the wasp was another species until I saw it was a grasshopper of the family Acrididae, which told me differently. Here at last was Prionyx thomae.

There are seven species of wasps in the genus Prionyx (family Sphecidae) found in the United States. Collectively they range across the entire U.S. and adjacent southern Canada, so there is probably at least one species calling your own geographic location home. All are “thread-waisted” wasps with a very globose abdomen and stout, spiny legs. Two species are entirely black in color (atratus and subatratus), while the remainder are black and red with silvery highlights.

These are solitary wasps, each individual female making her own nest, the same as the cicada killers I introduced last week. Both are also termed “parasitoid” species. Parasitoids invariably kill their hosts. The interesting thing about parasitoid wasps is that most species actively carry their victims to a storage site rather than leaving them in situ. This probably evolved to protect the wasp’s offspring, and their food, from predators and parasites.

Prionyx thomae has no common English name. Most insects that are of no economic importance have only a Latin or Greek name. This species, which ranges from the southeastern and western U.S. to Argentina, looks very similar to P. parkeri and P. canadensis. I have yet to find canadensis here in southeast Arizona, however, and parkeri can be readily identified by the two pairs of long palps, part of its mouthparts.

Back to the action. When Ned and I spotted this particular wasp, she was in the usual state of alertness and nervousness of most solitary wasps. She snapped at ants that blundered near her or her paralyzed grasshopper prey. She stopped on a rock and groomed herself. She maneuvered the grasshopper into a better location. Then she began to excavate a burrow in the damp, rocky soil. Apparently the audience was too much and she evidently abandoned the burrow and her prey.

The victim in this instance appeared to be a band-winged grasshopper, Conozoa carinata. Other recorded hosts for this wasp include Amphitornus, Aulocara, Orphulella pelidna, Arphia xanthoptera, Dissosteira Carolina, Encoptolopus subgracilis, and Paraidemona. Most of these are not small grasshoppers, and the ability of the wasp to lug around one of them over rugged terrain would be comparable to a person carrying a couch single-handedly.

The female wasp secures her prey before digging a burrow. The burrow can be curved, linear, or L-shaped, and ends in a single chamber that receives the single grasshopper victim. The wasp then lays an egg on it, exits, and seals the burrow entrance. She then leaves to repeat the process again.

During the process of digging and provisioning the burrow the wasp and her prey are both vulnerable to parasites. Chief among them are the “satellite flies” of the subfamily Miltogramminae (in the family Sarcophagidae). Satellite flies get their name from the way they “orbit” their hosts, waiting for a chance to deposit eggs on the wasp’s prey. The fly larvae that hatch then feed on the food that was intended for the larval wasps, effectively starving them to death. Such behavior is called “kleptoparasitism” when a parasite “robs” the host of its rightful resources. I took the image below in South Deerfield, Massachusetts. The wasp in this case was probably Prionyx canadensis.

There is no end to the dramas that take place on a macroscopic scale in your flowerbed, lawn, or child’s sandbox. You just have to be observant and interested. Then, I guarantee you, you will be entertained, mesmerized, and awed by how incredibly strong, intelligent, and energetic most insects are.

Saturday, July 24, 2010

100th Post: Meet Abigail Parker

I wanted to find a subject worthy of my 100th post to this blog, and I think I have one: My wonderful friend Abigail Parker. Abby is a highly intelligent and creative woman who has become a very respected authority on lady beetles (familyCoccinellidae) of North America. I finally had the pleasure of meeting her in person in south Texas last month.

We had known each other for a long while via, but it turns out Abigail is very knowledgeable about most natural history subjects. She taught me several birds during the Texas trip. I would not have recognized this Willet, for example, had she not told me what it was.

Her enthusiasm and patience are remarkable, especially considering that she battles medical issues that would leave most of us indoors whining and complaining at a minimum. The heat and humidity of Brownsville and Mission will leave the healthiest person exhausted, but Abby was a real trooper.

One of the things I love most about Abigail is that she maintains a “sense of wonder” and awe that most scholars lose along the way in academia. She’s quick to ask that you not be in awe of her own Yale education, but her friendly and conversational personality put you at ease anyway.

Our mutual friend Mike Quinn invited us to join him, and his colleagues, for blacklighting in the Laguna Atascosa National Wildlife Refuge. This was Abigail’s first time doing this kind of thing and she was in wonderland! It was great to see her enjoying herself, her friends, and the myriad of insects that flocked to the lights.

In “real life,” Abby lives with her husband in Philadelphia, Pennsylvania, where she also works for a small publishing company. Her interests beyond birds and ladybugs extend to gems and tarot cards. She is also a talented artist, as any visit to her Facebook page or Flickr photostream will reveal. She also has her own blog, ”Butterfly Psyche”, that you might check out.

During the Texas trip I was honored to treat Abby to a birthday dinner at a sushi restaurant in Mission. We both got “dressed up” and had a great time. I learned a good deal about sushi, too! There seems to be no limit to Abigail’s passions, knowledge, and achievements. Keep it up, Abby, and know you have many friends who care about you.

Wednesday, July 21, 2010

Wasp Wednesday: Pacific Cicada Killer

I have noticed for a long while that many nature bloggers and photographers dedicate one day a week to a particular type of organism. There is “Fly Day Friday” and “Moth Monday” to be sure, so I have decided to institute my own version of this, which I dub “Wasp Wednesday.” This will be a challenge since I don’t have many wasp images in my archives. Nevertheless, may I welcome you to the debut of this weekly feature and introduce the Pacific Cicada Killer, Sphecius convallis.

Many people are familiar with the Eastern Cicada Killer, Sphecius speciosus, as illustrated by the male specimen below. I took this image in the Montague Plains Wildlife Management Area in Franklin County, Massachusetts last year. This is only one of four species that occur in the United States. There is also the Western Cicada Killer, Sphecius grandis, and the Caribbean Cicada Killer, Sphecius hogardii, which ranges into southern Florida.

Cicada killers are named for their prey: Solitary females of this genus sting adult cicadas into paralysis and carry them back to their individual burrows as food for their larval offspring. The sight of one of these wasps flying back to its nest while carrying an equally large cicada will leave you in awe.

When not engaged in hunting or digging a nest burrow, or guarding a territory as the males do, Pacific Cicada Killers will seek refuge from the heat of the day in dense stands of vegetation. Here in southern Arizona, one can find them clinging to Desert Broom (Baccharis sarothroides) for example. I have found them nestled among cattails at an artificial riparian area in my neighborhood park here in Tucson.

Female cicada killers differ from males in behavior and morphology. Males are territorial, perching in places that overlook nesting aggregations of females, or sitting on the ground amongst the females. Males act aggressively toward other males, and other intruding organisms. They are “all bark,” however, since they possess no stinger. The spines at the tip of the tibia (“shin”) on the hind leg are short and not terribly obvious on males.

Female cicada killers have the spines on the hind tibia modified into heavy, blade-like appendages, clearly visible in the image below. They use these blades to help kick soil out of the burrow as they dig with the front legs. The female wasps are generally larger and bulkier than the males as well, but are too busy nesting and hunting to bother attacking people or any other animal.

Despite the solitary nature of their nests, cicada killers do tolerate each other’s company, and many females may nest in large aggregations in a small area. The burrow entrances are surrounded by the excavated soil (called “tumulus”) and are easily mistaken for the work of small rodents. Underground, the burrow may extend up to four feet, with individual cells branching from the main tunnel. Each cell is provisioned with one to four paralyzed cicadas. One cicada yields one male cicada killer. More cicadas will feed a future female.

Each cell is sealed after completion, and the entire nest burrow is eventually completed and sealed. The female does not stick around to care for her offspring. Instead she may start a new burrow.

Pacific Cicada Killers are known to use Apache Cicadas, Diceroprocta apache, and Silver-bellied annual cicadas, Tibicen pruinosus as hosts. It probably has other hosts in the Pacific Northwest where neither of these cicadas occurs.

Sphecius convallis ranges throughout the United States west of the 100th meridian (roughly west Texas, the Oklahoma panhandle, western third of Kansas and Nebraska, and the western half of the Dakotas). Please let me know if you find this species in your area, or in your travels. Please consult Professor Chuck Holliday’s Cicada Killer Page for information on how to tell this species apart from the Western Cicada Killer. His research is also suggesting there may be a cryptic species within the currently recognized Sphecius convallis, so your observations and/or specimens could prove quite valuable.

Saturday, July 10, 2010

Robber Flies

Robber flies are conspicuous denizens of the desert southwest, but are common nearly everywhere. You might be seeing them yourself but simply not recognizing what they are. No wonder. Robber flies, also known as “assassin flies,” often resemble wasps or bees more than they do flies. They certainly bear little resemblance to house flies. They don’t carry diseases or bite people, either. Instead, they are swift predators of other insects.

There are nearly one thousand species of the family Asilidae in North America north of Mexico, but that doesn’t mean they have all been discovered yet. I helped discover a new species of Laphria myself, in a park in Cincinnati, Ohio. Prior to my specimens, the species (still awaiting formal description) was known from only one other specimen collected in Pennsylvania.

Robber flies vary greatly in size (3-50 mm), shape, and color pattern. Some are robust bumble bee mimics. Others, like those in the subfamily Leptogastrinae, are slender and nearly invisible as they navigate through tall grasses.

There are some things to look for that are common to all robber flies, however. They have a deep, concave area between the eyes at the top of the head. This helps set them apart from similar flies like mydas flies (Mydidae) and dance flies (Empididae). Robber flies also often have a “bearded” face, with long hairs over their mouthparts. Even with the setae, the stout beak-like mouthparts are often visible.

Look for robber flies in a variety of habitats, from deserts to grasslands to forest openings with dappled sunlight. Robber flies like to perch on the ground, rocks, logs, tree trunks, or foliage where they have a great vantage point to scan the landscape and the sky above them.

Watch one on the tip of a twig or a leaf as it cocks its head toward insects passing overhead. The fly may leave its perch abruptly, but you should stay put. It may well return with a victim to dine on. Asilids are able to intercept flying insects in mid-air, much like a flycatcher bird does. Some species seem to have their food preferences, but most are generalists. Very large robber flies can kill insects as large as adult grasshoppers, or even dragonflies.

Members of the genus Diogmites are known as “hanging thieves” for their habit of swinging from the front or middle pair of legs while manipulating prey with the remaining two pairs, as the one above is doing with a skipperling it caught.

The bite of robber flies is administered with that beak, driven into joints in the exoskeleton of the prey insect. The “necks” of insects are especially vulnerable, and flying beetles are impaled while their elytra are open, exposing chinks in their armor. Paralytic compounds and digestive enzymes are likely injected during the bite as victims cease struggling almost immediately. The fly then withdraws the liquefied internal tissues of its meal.

As easily as adult robber flies are observed, the corresponding larval stage remains quite a mystery. Those species that have been reared are known to be external parasites of beetle grubs, or other insect larvae.

Before you set out into the field to find robber flies, it might help to become familiar with all the different genera you are likely to encounter. Remember that they often resemble insects other than flies. A good place to start learning is the image gallery at Click the “images” or “browse” tab near the top of the page to get more images. Another outstanding internet resource is the robber fly site built by Herschel Raney, an extraordinary nature photographer and self-taught expert on asilids. Three individuals are webmasters for a global robber fly website.

As the popularity of these amazing insects continues to grow, no doubt more resources will be created. For those who prefer printed to electronic references, my Kaufman Field Guide to Insects of North America includes two plates devoted to robber flies, with complementary text on the opposite pages.

Stop, listen (for a loud, droning buzz that stops abruptly) and look (carefully, for despite their size robber flies can be rather cryptic) for these winged wonders of the insect world. You will not be disappointed that you did.

Friday, July 2, 2010

False Chinch Bugs

I like to turn on the porch light at my Tucson, Arizona apartment to see what insects (and sometimes other organisms like Mediterranean Geckos) show up to visit. Well, most of the time I like to do this. Right now it is an exercise in annoyance as the porch light is quickly overwhelmed by tiny true bugs known as “False Chinch Bugs,” Nysius raphanus.

At only 3-4 millimeters, each individual bug is not terribly imposing. It is the sheer numbers of them that are a nuisance. They fly well and before you know it everything in the immediate vicinity is covered in them: you, your camera, your clothes, and any other objects close to the light source.

This tendency for Nysius to aggregate extends to their feeding habits as well. Hordes of them may literally suck the life out of certain plants, though they subsist for the most part on weeds. Severe damage to a variety of crops does occur on the rare occasions of large outbreaks of the false chinch bug. Their combined feeding, coupled with toxic secretions they inject in the course of feeding, can wilt foliage rapidly.

These insects are quite capable of migrating like a miniature swarm of locusts, too. They have been observed flying several hundred feet above the ground. It is suspected that an “aggregation pheromone,” a specific chemical compound emitted by the insects, is responsible for the mass behaviors.

Like all true bugs, false chinch bugs undergo “incomplete” metamorphosis. They hatch from the egg looking like miniature versions of adults, but lacking wings and reproductive organs. These babies are called “nymphs,” and they are sometimes mistaken for ticks by folks that find them on their clothing after a walk in a weedy area. They grow quickly, maturing in about three weeks. In some parts of North America they can produce three generations annually, overwintering as adults.

Thankfully, an onslaught of false chinch bugs is a brief phenomenon. They disperse within a few short weeks of their initial appearance. Meanwhile, they can be discouraged by keeping outdoor lighting to a minimum, and weeding in the spring to deprive them of the plants that they favor as nymphs.

There are many informative and reassuring internet resources for learning more about false chinch bugs, such as this fact sheet from Colorado State University Extension.

So far, my little population explosion seems minor by the standards I have read about, and until the monsoon rains kick in the diversity of species at my porch light will likely remain low anyway. Plus, leaving the light off should help ease my electric bill, or at least allow me the luxury of turning up the A/C a little higher.