Wasp Wednesday: Tenthredo

Sawflies are about as un-waspish as wasps can get. They don’t have a narrow “wasp waist,” the abdomen being attached broadly to the thorax. The females don’t sting. Their larvae are vegetarians instead of carnivores. They are rather soft-bodied and delicate. They are, however, very abundant at certain times of the year.

The specimen depicted above was identified as a male in the genus Tenthredo, family Tenthredinidae, by Dr. David R. Smith, a world authority on the broader group to which sawflies, horntails, and related primitive wasps belong: the Symphyta. The image was taken near the summit of Mt. Lemmon in the Santa Catalina Mountains of southern Arizona on an aspen leaf, June 12, 2010.

The genus Tenthredo includes approximately 118 species in the U.S. and Canada. The adult wasps are often seen on flowers, but they will eat smaller insects as well as pollen and nectar. Many species mimic stinging wasps like yellowjackets and spider wasps, but the females have no stinger. They retain an egg-laying organ called an ovipositor, modified into a saw-like blade used to insert eggs into plant tissues.

Larvae of sawflies in general are frequently mistaken for caterpillars, and indeed most behave in that manner: they feed on foliage just like a lepidopteran larva. How do you tell them apart then? Caterpillars have only five pairs of prolegs (those fleshy knobs down the length of their bodies that they use like suction cups to grip vegetation) or fewer, while sawfly larvae have seven pairs of prolegs. The larva shown below is typical of sawfly larvae, though it may not be a member of the genus Tenthredo. The image was taken September 6, 2009 at Knightville Dam in western Massachusetts.

Adult sawflies have fairly complex wing venation that gives the wings a reticulated appearance. The common sawflies in the Tenthredinidae family have triangular faces, with slightly bulging eyes, as seen in the image below, also taken at Knightville Dam.

Look for sawflies mostly in the spring, especially at the edges of deciduous forests. Those in the genus Tenthredo actually tend to appear later, in the late summer and early autumn. Watch for larvae in groups feeding on leaves. Watch this space for more on other kinds of sawflies as I encounter them afield.

Wasp Wednesday: Chirotica

I never expect to encounter wasps in the middle of December, but then I also don’t go out looking for them at that time of year. A trip to the Sabino Canyon Recreation Area north of Tucson on December 19 has me re-thinking that assumption. I was surprised by the number and diversity of wasps I saw. Among the more interesting was an ichneumon wasp I later identified as belonging to the genus Chirotica.

Fred Heath, a volunteer naturalist at Sabino Canyon, had invited me along for a short hike in the late morning and early afternoon. He knows the area very well and was able to point out everything from plants to puffballs. On a willow tree full of bagworms (moth family Psychidae), a flash of movement caught my eye. A very elegant-looking ichneumon wasp was exploring one of the branches of the willow.

Ichneumons are notoriously quick to fly at the slightest movement, so I did not expect this wasp to stick around. Much to my surprise it simply continued its searching behavior, allowing me a couple images with my camera before it departed. What was this female looking for?

It turns out that the four North American species of Chirotica are parasites of….bagworms! It all made sense, and a series of images on the website Bugguide.net even show one of these wasps investigating a bagworm cocoon.

The “stinger” on my specimen is actually the female’s egg-laying organ, called an ovipositor. She does not use this structure as a weapon in self-defense and so is harmless to inquisitive people like me. Not that I could have caught her by hand anyway.

Anyone with an infestation of bagworms would likely welcome more of these wasps, but I honestly have no idea just how common (or scarce) they are. You can learn about the known distribution of our four species by using the Database of Hymenoptera in America North of Mexico. Bob Carlson, an expert on ichneumon wasps who is now retired from the National Museum of Natural History (Smithsonian) put together that part of the database.

Ichneumons are among the most diverse group of insects on the planet, so even an “armchair entomologist” can make significant contributions to science by documenting specimens through collection and imaging, but especially through rearing the wasps from host insects like butterfly and moth caterpillars.

Pygmy Mole Crickets

I know! What the heck is a “pygmy mole cricket?” Well, they are actually more akin to short-horned grasshoppers than mole crickets. I have known about them for some time, but finally saw two “in the wild” in the Sabino Canyon Recreation Area last Sunday, December 19.

The family Tridactylidae occurs on all the major continents except Antarctica, but most species are apparently tropical. There are only two species currently recognized in North America, and the one I encountered is likely Neotridactylus apicalis, the “Larger Pygmy Mole Cricket.” That species ranges from extreme southern Ontario east to Massachusetts, south to Florida, and west to southern California.

At about the size of a grain of rice (ok, from 5.5-10 mm), they are not very noticeable. Couple that with their habit of tunneling under the sand along the margins of streams, rivers, ponds and lakes, and it is no wonder they are not more familiar to naturalists. They move rather slowly, or at least this pair did as they crept up the surface of a streamside boulder. The hind legs of these insects are positively enormous, and the hind femora alone usually conceal the folded wings of the adults. The front wings are leathery and reduced to short stubs, while the membranous, pleated hind wings extend just beyond the abdomen when folded.

I was pleased that these individual specimens were so tolerant of a close approach with my camera (though I wished for a really good macro lens), because when they finally did decide to jump….Game over! They seemed to disappear into thin air. There was certainly no finding them again.

The physics of these jumps is remarkable, as revealed in the abstract for ”Jumping Mechanisms and Performance of Pygmy Mole Crickets” in the Journal of Experimental Biology, 2010 Jul 15;213(Pt 14):2386-98, by M. Burrows and M. D. Picker. Were a human even capable of such a feat, he would likely pass out from the G-force alone.

Pygmy mole crickets, which are also known as pygmy sand crickets or pygmy mole grasshoppers, apparently ingest sand particles and whatever algae and other organic matter adheres to them. Their subterranean burrows extend 2-3 centimeters below the surface, and females create brood chambers at the bottom of their tunnels.

Do keep an eye out for these little wonders. You are likely to find other insects in the same habitats, like the grouse locusts I’ll discuss in the next week or two. Happy hunting.

Wasp Wednesday: Campsomeris

I could never have imagined that I would confront another mystery wasp in the middle of December, but there it was: an e-mail from a friend describing what I knew (even in the absence of an image) was a species of wasp that had been recorded only recently in Arizona, and far closer to the Mexican border than in the Sabino Canyon Recreation Area where my friend’s sighting took place.

Fred Heath is an outstanding naturalist, author of the Introduction to Southern California Butterflies, and a member of the Sabino Canyon Volunteer Naturalists. On a visit to the area on Tuesday, December 14, he and others spied a male specimen of Campsomeris ephippium on blooming flowers of Desert Lavender (Hyptis emoryi). Fred didn’t get an image, but this wasp is so conspicuous and distinctive that it didn’t matter.

Fred posted a message on the e-mail list for the Sabino Canyon Volunteer Naturalists, sparking David Lazaroff, a founder of the SCVN, to go looking himself, camera in hand. The above image is used with David’s permission, and what a great picture it is. The long antennae, relatively slender body, and “pseudostinger” at the posterior of the abdomen reveal the gender of this specimen. Females, more robust with shorter antennae, have the real deal: a retractable stinger used to subdue the scarab beetle grubs that are the hosts for its larval offspring.

I would not have known what this was had it not been for this image from the spring of 2009. Up until that time, Campsomeris ephippium was known only from south Texas, and south to Ecuador.

Fred Heath and I went back to Sabino Canyon on Sunday, December 19, but failed to find the beast. Ironically, we did manage to spot a few males of the common local species, Campsomeris tolteca. They were hungrily feeding on the nectar of Coreocarpus arizonicus (Little Lemonhead) beside Queen butterflies and Mexican Yellows (also butterflies).

Campsomeris wasps belong to the family Scoliidae, all of which are known parasitoids of scarab beetle grubs. A parasitoid is a parasite that invariably kills its host. Female scoliids, with their heavy, spiny legs, dig up a scarab grub, sting it into brief paralysis, and then lay a single egg on the beetle larva. Then the wasp leaves the scene. The grub eventually regains consciousness and control over its motor skills (such as they are), resuming its underground existence feeding on the roots of plants. Meanwhile, the wasp egg hatches and the wasp larva begins feeding as an external parasite of the beetle grub.

I hope to eventually find more specimens of Campsomeris ephippium, and females of some of our other scoliid species here in Arizona, but I certainly enjoy the pleasure of the hunt regardless of the outcome. Special thanks to Fred Heath for allowing me to join him in the great outdoors. Thanks again to David Lazaroff for use of his fine image.