Wasp Wednesday: Ageniella accepta/conflicta

Expert entomologists caution that species-level identifications cannot always be made from images of live specimens in the wild. Such is the case with most spider wasps of the family Pompilidae. It is difficult enough to get any image, unless the wasp is enjoying flower nectar and oblivious to anything else, or digging a burrow and intent on her activities. So, I preface this article by stating that I can’t be certain the species depicted here is Ageniella accepta or A. conflicta.

When I first spotted one of these wasps running around on a sunflower plant here in Colorado Springs, I passed it off as just another kind of ant. Indeed, ants rule the sunflowers, driving off any insects that want to lick the sweet, sticky substance exuded by the plant. Closer inspection revealed that this was no ant. The extra-long legs were one clue. So was the fact that it was winged, but the dark bands across the wings give the impression of the “nodes” that link an ant’s abdomen to its thorax.

Why mimic an ant? Ants are, like wasps, members of the order Hymenoptera. They defend themselves and their nestmates by biting viciously, stinging, or squirting formic acid. Not many predators want to mess with them. Further, where there is one ant there are usually more, quick to come to the aid of a fellow worker in distress. Any insect (or even spider) that looks like an ant is probably going to be left alone by its enemies.

From previous experience, I know that small orange and brown pompilids with banded wings are likely going to be females in the genus Ageniella. I encountered the one below at the Orange Municipal Airport in Massachusetts on September 7, 2009. She was toting a spider, its legs amputated to presumably facilitate easier transport. Nick Fensler, an expert on spider wasps of eastern North America, kindly identified it for me as probably Ageniella conflicta.

Females of that species apparently hunt immature wolf spiders (family Lycosidae) as food for their larval offspring. Varacosa gosiuta, V. avara, Arctosa littoralis, and Pardosa valens are among the recorded hosts for Ageniella conflicta. Jumping spiders have also been recorded as prey, but that was before even the experts could tell conflicta from accepta.

The amputation of the legs also makes it easier for the female wasp to stuff her victims into narrow openings. The wasps dig short burrows that originate in pre-existing crevices in the soil. Little else is known of their nesting habits and life cycles.

It should be noted that males of both species look completely different from females: They are black with some reddish markings on the legs, and a white spot on the tip of the abdomen, as shown below. Neither gender is very large. The forewing length for females is 5-8 millimeters, and 4-5 millimeters for males.

Ageniella accepta visits other plants besides sunflowers, including nectaries of Chamaecrista nictitans (Sensitive Partridge Pea), and flowers of Euphorbia marginata (Snow-on-the-Mountain), Baccharis salicifolia (Seep Willow or Mule-fat), and Bifora Americana (Prairie Bishop).

Ageniella accepta ranges across most of the southern half of the United States and into Mexico. This is one of at least three North American species in the “accepta species group.” The widespread A. conflicta and the western A. blaisdelli are the others, according to Townes (1957).

The scarcity of information about our species of Ageniella means that your own observations could be quite meaningful. Next time you think you see an ant, double check and see if it isn’t actually one of these unique spider wasps.

Sources: Evans, Howard E. and Carl M. Yoshimoto. 1962. “The Ecology and Nesting Behavior of the Pompilidae (Hymenoptera) of the Northeastern United States,” Misc Publ Entomol Soc Am 3(3): 67-119.
Kurczewski, Frank E. 1975. “Host Records for Some Species of Pompilidae From the Southwestern United States and Mexico,” Pan-Pac Entomol 51(2): 147-151.
Kurczewski, Frank E. and Edmund J. 1968. “Host Records for Some North American Pompilidae (Hymenoptera) With a Discussion of Factors in Prey Selection,” J Kans Entomol Soc 41(1): 1-33
Townes, Henry. 1957. “Nearctic Wasps of the Subfamilies Pepsinae and Ceropalinae,” U.S. Nat. Mus. Bull. 209: 1-286.

Spider Sunday: Sassacus

It is often difficult to tell whether a particular spider specimen is an adult or an immature, especially if you go by size alone and don’t know how large an adult is supposed to be. Take the jumping spider genus Sassacus for example. The adult animal is only about 3-5 millimeters (male) or 4.4-5.5 millimeters (female). The specimen pictured here is an adult female, probably gravid, that I spotted on the leaf of a sunflower plant here in Colorado Springs on July 28 of this year.

The origin of the genus name is an interesting slice of history. According to Bugguide.net, “Sassacus” was the last chief of the Pequot Indians, a Native American tribe of the Connecticut Valley that was vanquished in a war with English settlers in 1637.

The iridescent color and very compact appearance of these spiders leads scientists to suspect that they are mimics of certain leaf beetles in the family Chrysomelidae. Many chrysomelids just don’t taste good, or they feed on poisonous plants and sequester those herbal toxins for their own defense. They advertise their distastefulness to predators with bold black and white, yellow, orange, or red color patterns, or with bright metallic colors.

Depending on which authority you consult, there are either three or nine species of Sassacus in North America, including Mexico. Richman (2008) revised the genus to include the former genus Agassa, and one species group from the genus Metaphidippus. Collectively, the genus occurs from southern British Columbia south into Central America. It is widespread in the U.S. Sassacus papenhoei and Sassacus vitis have both been collected here in Colorado.

One of the defining characteristics of this genus is the very short legs. The fourth pair of legs is the longest, followed by the third pair. The first pair of legs is still the thickest, with one or two pairs of spines, used in tackling prey. I believe the female in these images is missing one of her front legs, but if so she disguises her injury well.

Like most jumping spiders, Sassacus engages in visual courtship displays. It turns out that twitching the abdomen also produces an auditory stimulus, which scientists have recorded in the laboratory (Maddison and Stratton, 1988). Males make zigzag or spiral approaches to the female at first, raising and crossing their front pair of legs once they have a female’s attention. Later, they raise and lower their front legs until they are accepted or rebuffed (Richman, 1982).

There are some “normal” species in the genus that are more spider-like than beetle-like, but the ones you are likely to encounter are going to be the beetle mimics covered in those iridescent scales. Look for Sassacus on broadleaved plants in open fields and along forest edges, but don’t expect them to be common. I was surprised how few “popular” spider references included the genus.

Sources: Fitch, Henry S. 1963. Spiders of the University of Kansas Natural History Reservation and Rockefeller Experimental Tract. University of Kansas Museum of Natural History Miscellaneous Publication No. 33. 202 pp.
Kaston, B. J. 1978. How to Know the Spiders (Third Edition). Dubuque, Iowa: Wm. C. Brown Company Publishers. 272 pp.
Maddison, Wayne P. and Gail E. Stratton. 1988. “A common method of sound production by courting jumping spiders (Araneae, Salticidae),” Journal of Arachnology 16(2): 267-269.
Richman, David B. 2008. “Revision of the jumping spider genus Sassacus (Araneae, Salticidae, Dendryphantinae) in North America,” J. Arachnol. 36(1): 26-48.
Richman, Daved B. 1982. “Epigamic display in jumping spiders (Araneae, Salticidae) and its use in systematics,” J. Arachnol. 10: 47-67.
Richman, David B. and Robert R. Jackson. 1992. “A review of the ethology of jumping spiders (Araneae, Salticidae),” Bull. Br. Arachnol. Soc. 9(2): 33-37.

Wasp Wednesday: Euodynerus annulatus

Back on July 9, 2012, I visited the Florissant Fossil Beds National Monument in Teller County, Colorado. The area is well-known for amazing specimens of fossil insects, but the ones that live there now are pretty interesting, too. Take, for example, the mason wasp Euodynerus annulatus.

This species is widespread, found from coast to coast in the United States, south to Mexico; and in the Canadian provinces of British Columbia, Alberta, Saskatchewan, and Ontario (though the last record for Ontario was in 1954; and the record for Saskatchewan is very recent). There are five subspecies, three of them western in their distribution. The color and markings vary considerably among those different subspecies.

These are also fairly sizeable wasps, the length of the front wing varying from 8.5-10.5 millimeters. The species could be confused with the very common Euodynerus hidalgo, but the propodeum (hindmost segment of the thorax) is not as angulate in E. annulatus. The hind margins of the first and second dorsal abdominal segments (tergites) are also not clear and reflexed (turned up) as they are in E. hidalgo.

What surprised me the most about this wasp was learning that instead of using pre-existing cavities, or making mud nests, females of Euodynerus annulatus excavate burrows. Not only that, but they extend the tunnel aboveground as a curved mud “chimney.” Several individual cells branch from the main burrow underground. This wasp does not seem to be particular about the soil type, finding hard soil or soft soil perfectly suitable for its nest. The species does seem to favor situations close to water, as the female will regurgitate water to soften the soil during nest-building.

The chimney might help make the nest easier to defend from potential parasites, but it apparently serves as the source of mud pellets to make the final nest closure as well. Eventually, the turret is deconstructed entirely and the nest entrance made nearly invisible and flush with the surrounding soil (Rau and Rau, 1918).

The female wasps use caterpillars from the moth families Crambidae, Pyralidae, and Noctuidae as food for their larval offspring. The caterpillars are only weakly paralyzed (Rau and Rau describe some instances in which the larvae were still ambulatory), usually several placed in each cell. A single egg is suspended from a short thread attached to the wall of the cell before it is stocked with caterpillars. When all cells are provisioned, the nest entrance is sealed and the wasp leaves to begin a new nest.

Caterpillars of the genus Loxostege were recorded as a major host by Rau and Rau, and certainly the Alfalfa Webworm and its relations are exceedingly abundant here along the Front Range. Here’s what the adult moth looks like:

Male specimens of Euodynerus annulatus can be recognized by the hooked tips of the antennae, and their less robust appearance. I found both a male and female taking nectar from an early-blooming rabbitbrush plant (Ericameria sp.) at Florissant Fossil Beds.

Ironically, while no nest parasites are recorded for this mason wasp, the adult wasps are vulnerable to a type of insect called a “twisted-wing parasite,” Pseudoxenos hookeri. Parasitized wasps will have bulges in the abdomen, with what look like bullets wedged between abdominal segments. More on these bizarre animals in a future post.

I must thank Dr. Matthias Buck, Associate Curator of Invertebrate Zoology at the Royal Alberta Museum in Edmonton for identifying the wasps in these images, and describing a bit of their biology. I am hoping to get him down to Colorado at some point to see for himself the amazing diversity of Eumeninae to be found here.

Sources: Buck, Matthias, Stephen A. Marshall, and David K.B. Cheung. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5: 492 pp (PDF version).
Krombein, Karl V., et al. 1979. Catalog of Hymenoptera in America North of Mexico (volume 2 Apocrita (Aculeata). Washington, DC: Smithsonian Instititution Press. 2188 pp.
Rau, Phil and Nellie. 1918. Wasp Studies Afield. Princeton, NJ: Princeton University Press. 372 pp. (Dover edition, 1970). Note that Euodynerus annulatus is described as Odynerus geminus on pages 300-312.

Spider Sunday: Breaking News

I was debating with myself about what species to feature in this week’s “Spider Sunday,” when I got wind of a story that immediately trumped all other options. Not only was there the formal announcement of a new species of spider, but one that represented an entirely new family of spiders as well. It takes a very unique species to demand its own family, but this arachnid is strange indeed.

Several press outlets carried the story, many including images of this odd spider. Not surprisingly, there is some conflicting information and perhaps exaggeration.

What is known for certain is that the spider had to be formally described and named before the discovery could be made public. That official record is in the latest issue of the professional journal ZooKeys, a peer-reviewed online publication of Pensoft Publishers. This in itself is newsworthy. Online journals shrink the timeline between discovery of species and the broadcast of those discoveries. Even so, this spider was found initially in 2010. Online journals also mean that you don’t have to live next to a university library to be able to access authoritative serial publications.

Let’s get back to the spider, though. What makes it unique? There is no question that the most distinguishing feature is the long, articulated, blade-like claws on the tip of each leg. The spiders are found on the ceiling of caves in southern Oregon (one report included northern California and British Columbia in the distribution), suspended upside down in very small, minimalist webs. It is thought that they wait for small, flying insects to come within range of their lanky legs, then hook their prey with those sickle-like claws.

These are not small animals. The legspan of a mature specimen can exceed two inches (five centimeters). As scientist Charles Griswold, the lead author in the journal article, explained in a BBC radio interview, they look even larger in the beam of a headlamp. The spiders are not blind, but have only six eyes as opposed to the usual eight for most spiders. Live specimens in Griswold’s lab at the California Academy of Sciences refused to eat.

The last time a new species of spider required the erection of a new family was back in 1990, when a South African spider was described. You have to go back to the 1890s to find the last time a new family of spiders was established for a North American spider.

The new family is named Trogloraptoridae. The spider’s official species name is Trogloraptor marchingtoni. The genus name is a combination of Greek and Latin that translates to “cave robber.” The species is named for Neil Marchington, a deputy sheriff for Deschutes County, Oregon, who first showed scientists the spiders inside a cave. Marchington is also a member of the Western Cave Conservancy and an amateur biologist.

Cave organisms in general are poorly understood, and highly vulnerable. Populations of cave animals tend to be small, specifically adapted to a lightless habitat, and prone to perish with the slightest change in that environment. It is largely thanks to the efforts of organizations like the Western Cave Conservancy that any effort at all is made to preserve and protect caves. Irresponsible spelunkers (cave explorers) can easily damage a cave just by touching formations and thereby changing the chemistry that forms caves. Vandals can deface and destroy caves; and development above a cave can result in contamination of groundwater that courses through the cave, if not causing the cave to collapse in part or in its entirety.

I take special delight in learning that this new species was found in my home state of Oregon. The coniferous forests there have relatively poor biodiversity compared to deciduous forests, deserts, and rainforests, but there is no argument that the species found in the Pacific Northwest are often unique. I hope to get back there again in the future, if only to find insects and spiders that I know exist there, but that I have never seen. I’ll have to add this spider to that list!