Wasp Wednesday: Spilichneumon

One of the more common early spring wasps here in the Front Range of Colorado is an ichneumon wasp in the genus Spilichneumon. According to the Database of Hymenoptera in America north of Mexico there are at least four species in the state, so perhaps I am seeing more than one.

These wasps are active and skittish enough that they defy my ability to get really crisp images of live specimens, but I have found two deceased individuals on bike trails here in Colorado Springs. Plus, my fiancée found one at the Cheyenne Mountain Zoo. This specimen is shown below.

These wasps overwinter as adults, inside rotten logs and other protected situations, so they are among the first wasps one is likely to encounter by winter’s end.

Members of the genus Spilichneumon are not well-known, at least in the western U.S. The global range of the genus is the northern hemisphere (termed “holarctic”), and Oriental. Here in North America, most species are found in the extreme northern U.S., Canada, and Alaska, and along major mountain ranges as far south as Arizona.

This is yet another wasp you can count among your friends. Spilichneumon is an internal parasite of noctuid moth caterpillars. The female wasp finds a caterpillar and injects a single egg into it. Her larval offspring then feeds inside the caterpillar, allowing the host to eventually graduate to its pupal stage. The wasp larva pupates inside the host and emerges from the host chrysalis as an adult wasp.

I wonder if Spilichneumon competes with the cutworm-hunting sphecid wasps in the genus Podalonia? Both go after the same prey, at least in part, but Podalonia appears to be far more abundant here than the ichneumons. My observations may be biased, however, since I am usually out at the warmest part of the day, when Podalonia is most active. Spilichneumon, and other genera in the subfamily Ichneumoninae, tend to shun extreme heat and direct sunlight.

Look for this genus where you live. See Bugguide for better images. Look on the forest floor in open woodlands, as the wasps tend to seek their prey among leaf litter.

Wasp Wednesday: Liris

Last “Wasp Wednesday” I featured some very early emerging ”Winter Wasps” that I have recently encountered during the unseasonably warm weather here in Colorado Springs. Today I’ll focus on one of those: Liris. They are among the first solitary wasps of the family Crabronidae that you are likely to see in the spring. That is because the females overwinter as adults.

Beyond the early appearance of these wasps, I find other characters at least semi-reliable for distinguishing Liris from other members of the tribe Larrini. The antennae, frequently held parallel and straight out from the head, are proportionately longer in Liris than in Tachytes and Tachysphex. Tachysphex is usually considerably smaller than Liris, often with the abdomen entirely red, or red in part, and terminating in a very pointed pygidium. Tachytes frequently has bright green eyes, and is generally stockier in appearance than Liris. Tachytes rarely sit still for more than a millisecond (or so it seems), whereas Liris seems to move at least slightly more slowly.

Liris is a large genus with most of its diversity in the tropics. Over 260 species are known worldwide, but that is likely to increase substantially since the genus is poorly known in the New World tropics and in Asia. Krombein and Gingras revised the North American species (including Mexico) in 1984, but only two species, L. argentatus and L. beata are consistently found north of the extreme southern U.S. Species identification hinges on obscure characters like the male genitalia, female pygidium (a triangular plate on the last dorsal abdominal segment), and the size and shape of the sensory areas on the antennal segments. When the reference includes electron microscopy images, you can forget about making species identifications in the field.

illustration by Judy Jay (Bohart & Menke, 1976)

Still, I am willing to bet that the species I am observing here in Colorado Springs is Liris argentatus. It is by far the most abundant of all North American species in the genus, and found from southern Ontario and Massachusetts west to southeast Washington state, south to Panama. It is also one of the most studied species, so there is a wealth of information on its biology and behavior.

Females of L. argentatus vary from 9.5-15.4 mm in body length. Males are 6.4-10.7 mm. They are thus medium-sized insects. Both genders are black, but covered in fine, short, reflective hairs that give them a decidedly silvery appearance in bright sunlight.

My observations over the last two weeks indicate that one of the first priorities of newly-emerged females is to find water. Indeed, I have seen at least three individuals, on two separate occasions, taking water from damp soil in otherwise dry arroyos in Red Rock Canyon Open Space and Garden of the Gods, right around noon or one o’clock PM.

Both sexes will also seek fuel in the form of honeydew secreted by scale insects, and nectar from flowers as diverse as thistle, sunflower, wild carrot, and goldenrod.

The females next prepare nest burrows. Lacking a strong rake of tarsal spines on their front legs, females of L. argentatus may clean out pre-existing tunnels and cavities to use as nests. There are still plenty of records of this wasp digging its own burrows, terminating in one to three underground cells (one recorded nest had a cluster of ten cells). The nest varies from 10-14 centimeters in depth and is left open while the wasp begins its search for prey.

Crickets in the family Gryllidae are the host animals sought by these wasps. Both adult crickets and nymphs are taken. The prey is paralyzed by the wasp’s sting, facilitating easier transport of what is truly a bulky animal. The wasp grasps the prey by the base of its antennae and lugs it overland on most occasions. One to four (sometimes more) crickets are placed in each cell at the bottom of the burrow, an egg laid on the last victim. Oddly, the crickets are not completely paralyzed, recovering the ability to walk weakly, or even jump in some cases.

Once a nest is filled, the wasp fills the tunnel loosely with a combination of soil particles and fragments of dry vegetation, small pebbles, and other debris. She hides the entrance by kicking sand or soil over it, then leaves to repeat the whole scenario again.

Nests constructed in spring are remarkably devoid of parasites, but then the “satellite flies” that plague so many solitary wasps have not yet emerged themselves. Even velvet ants are only just beginning to stir. Nests made in the summer do suffer parasitism.

Those late-season wasps that do make it will mate before winter. Only the females live through the cold months, evidently inside burrows they dig for the purpose of hibernation.

Those of you in the U.S. and Canada can probably find these wasps in your own area very soon, if not right now. Please feel free to share your comments and observations here. There is still so much to learn about even the most common of insects, and you could be the one to make a significant contribution to our collective body of knowledge.

Sources: Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World: A Generic Revision. Berkeley: University of California Press. 695 pp.
Krombein, Karl V. and Sandra Shanks Gingras. 1984. “Revision of North American Liris Fabricius (Hymenoptera: Sphecoidea: Larridae),” Smithson. Contrib. Zool. No. 404. 96 pp.
Kurczewski, Frank E. and Margery G. Spofford. 1987. “Further Observations on the Nesting Behavior of Liris argentatus (Hymenoptera: Sphecidae),” Gt. Lakes Entomol. 20(3): 121-125.
O’Brien, Mark F. and Frank E. Kurczewski. 1981. “Nesting and Overwintering Behavior of Liris argentata (Hymenoptera: Larridae),” J. Georgia Entomol. Soc. 17(1): 60-68.

Spring Break!

I am taking advantage of the unseasonably warm weather this week (71°F today, predicted to stay that way or go higher through Saturday) to explore various wild areas around Colorado Springs. It means I won't be doing many blog entries now, but will have fodder for later entries. Also, I'm running low on wasps I have images of!

Do consider visiting my Flickr photostream this week, as I'll be posting new images there. Thank you and have a great rest of the week!

Spider Sunday: Spring Spiders

It really isn’t quite spring here on the Front Range, but neither is it winter, at least not lately. The high temperature for Tuesday, March 6 was 69°F, albeit windy. Walking down the Homestead Trail in Colorado Springs at midday I was amazed by how many spiders were out and about as well.

A surprising number of spider species overwinter as adults or immature, forsaking the cozy shelter of an egg sac in which to endure the harsh, cold extremes. Among them are running crab spiders (family Philodromidae, image below), crab spiders (Thomisidae), wolf spiders (Lycosidae), and jumping spiders (Salticidae).

Most of these arachnids are ground-dwellers, so presumably they ensconce themselves in debris such as leaf litter, or tuck themselves into the base of grass tussocks. Even a blanket of snow helps insulate spiders from colder air temperatures and chilly winds.

Spider bodies also contain glycerol, a chemical compound that helps reduce the freezing point of their blood, by about one degree Centigrade (Celsius). Certain proteins in spider blood (hemolymph) apparently reduce the freezing threat even more, up to 20°C. Spiders of temperate climates that overwinter in a passive state tend to be much more cold-hardy than those that are winter-active, like some wolf spiders in the genus Pardosa.

Spiders fall into different categories depending on their reproductive cycle. “Eurychronous” species take a long time to reach maturity, and so may overwinter as adults or immatures. “Stenochronous” spiders include those that reproduce during spring and summer (overwintering as immatures); those that mate in autumn (with the spiderlings overwintering inside the egg sac); and those spiders that are active during the winter, reproducing at that time. Lastly, “diplochronous” species have two reproductive cycles, one in the spring and one in the fall. Typically, they overwinter as adults.

The most abundant adult spiders I have found recently are running crab spiders in the genus Thanatus, family Philodromidae. Numerous specimens were basking on the concrete path of the Homestead Trail. A gust of wind caught one unfortunate specimen, sending it tumbling head over heel, heel, heel, heel, heel, heel, heel, heel.

One short stretch of trail also produced two very gravid female crab spiders in the genus Xysticus. “Gravid” means full of eggs. I’ll be looking for them next in silken retreats guarding their egg sacs. Crab spiders are typically ambush hunters, lying in wait for a potential victim to come within reach. Their extra-long first and second pair of legs means that “reach” is considerable, and spines lining the inside of their legs help insure that prey does not escape the spider’s embrace.

Wolf spiders are also on the move, and a short distance from the crab spiders I spotted a plump adult female heading for cover at the edge of the trail. Fortunately, she stopped just short momentarily, posing for a couple of pictures. My friend and colleague Mandy Howe kindly identified this as a female in the genus Alopecosa. She’ll soon have an egg sac attached to her spinnerets (the spider, not Mandy!).

I also found another wolf spider, much smaller and quicker. This is probably an immature in the genus Schizocosa, judging by its color pattern. It bears a superficial resemblance to the Thanatus in that both have stripes on the cephalothorax and a dark “cardiac” mark on the top of the abdomen. This pattern is effective camouflage among grasses and seeds, rendering the animals nearly invisible unless they move. I appreciate the concrete substrate for photography, as one easily loses track of the subject on a more natural surface.

Hiking in Red Rock Canyon Open Space on March 5, a 68°F day, yielded a pair of jumping spiders along the trail. I only managed to get the image below before the tiny arachnid hopped away. I have no idea whether it is an immature or an adult, let alone what genus it might be.

I encourage you to go spider-hunting yourself on the next nice day. It need not be that terribly warm, and I have seen spiders on the surface of the snow before. Look carefully, as some of the most abundant spiders of winter and early spring are the tiniest: dwarf spiders in the subfamily Erigoninae of Linyphiidae. Some juvenile cobweb weavers (Theridiidae) and funnel weavers (Agelenidae) can also be common.

Source: Foelix, Rainer F. 2011. Biology of Spiders (Third Ed.). Oxford, UK: Oxford University Press. 419 pp.