Tiny Wasp Hero Slays Redback Spiders in Australia

Spider wasps in the family Pompilidae are fearless hunters of arachnids as small as jumping spiders and as large as tarantulas (the "tarantula hawk" wasps), but I was unfamiliar with any species of pompilid going after cobweb weavers in the family Theridiidae. That was until late last week when these stunning images came across my Facebook news feed.

Abel González snapped these images of a female Agenioideus nigricornis spider wasp carting a paralyzed Redback Spider, Latrodectus hasselti, back to a nest burrow in Oldbury, Western Australia. The significance of this behavior requires a bit of backstory.

The Redback Spider is one of the most dangerously venomous arachnids in Australia. Indeed, it is in the same genus as the widow spiders of North America: Latrodectus. Any organism that targets such a potentially lethal animal deserves some acclaim. Oddly, we have species of the wasp genus Agenioideus here in the U.S. as well. I witnessed a female A. humilis hauling a comatose orb weaver here in Colorado Springs last year, and even posted about it, complete with video, in this blog entry. Our New World species do not go after cobweb weavers, let alone widows.

The initial discovery of the relationship between the Australian A. nigricornis and the Redback Spider is credited to a nine year-old boy, who spotted a wasp dragging a spider in his backyard in Beaconsfield, Western Australia. The young lad pointed out the drama to his father, who was astute enough to collect the two animals and photograph the habitat. The specimens eventually crossed the desk of Andy Austin, a professor at the University of Adelaide, who identified them.

This is not a big wasp. Females are only 8.24-13.11 millimeters in body length. Perhaps their diminutive size helps them navigate the labyrinth that is a Redback Spider's web. It is apparently still a mystery how the wasp manages to subdue its prey to begin with.

Back here in the U.S., the only spider wasp thought to be a potential predator of widows is Tastiotenia festiva, based on one circumstantial record from Rodeo, New Mexico. The range of T. festiva is restricted to the extreme southwestern U.S. One other wasp is very well known as a predator of widows. It is the Blue Mud Dauber, Chalybion californicum, a very widespread member of the family Sphecidae.

The Australian wasp was known to science as far back as 1775, when it was first described from specimens collected by Captain James Cook in 1768; and it is a common insect found throughout Australia. The fact that its host was unknown until the 21st century speaks to how much we have yet to learn about even the most familiar of invertebrates.

Sources: Krogmann, Lars, and Andrew D. Austin. 2012. "Systematics of Australian Agenioideus Ashmead (Hymenoptera: Pompilidae) with the first record of a spider wasp parasitizing Latrodectus hasselti Thorell (redback spider)," J. Aust. Entomol. Soc. 51: 166-174.
Staff. 2012. "Killer Spider Meets Its Match in Tiny Wasp," LiveScience.
Wasbauer, M.S. and L.S. Kimsey. 1985. "California Spider Wasps of the Subfamily Pompilinae," Bulletin of the California Insect Survey. Vol. 26: 1-130.

Spider wasp, Dipogon calipterus

Forest edges are a great place to look for wasps. Male wasps may perch on leaves to defend territories and look for passing females. Female wasps often hunt for prey among foliage, flowers, and stems. Both genders may pause to groom and rest on sunlit leaves. I was lucky enough to catch a rarely-seen spider wasp, Dipogon calipterus, grooming herself on a leaf at the edge of a wooded area near Bloomington, Indiana on June 20 of this year.

Dipogon spider wasps are mostly forest-dwellers that hunt for spider prey on tree trunks. Most species have dark bands on the wings, which have the effect of making them look a lot like ants. Considering that many predators dislike ants, it is an effective disguise. Add to that the fact that there is frequently a good deal of ant traffic going up and down any given tree bole, and it is no wonder these wasps are rarely observed.

These are not very large wasps, either. Townes (1957) measured wasps by length of the forewing rather than body length, and male D. calipterus have a forewing length of only five millimeters, females a forewing length of 5.7-7.4 millimeters. The wooded habitat and banded wings help to identify these wasps to genus. The reddish front legs help identify the species.

The distribution of Dipogon calipterus is scattered according to the three recognized subspecies. The one depicted here is D. calipterus calipterus, and it ranges from Massachusetts to North Carolina, Indiana, and Illinois, though it is important to note that our knowledge of the geographic distribution of most insect species is incomplete. D. calipterus duplicatus occurs in Georgia and Florida, and D. calipterus nubifer ranges from southern California to Panama. Slight differences in color and pattern seem to be the factors used in segregating the subspecies.

Females of Dipogon rarely, if ever, visit flowers for nectar, but are among the few wasps that will sometimes kill prey specifically to feed themselves rather than their offspring (or they feed on the spider before using it to provision a nest). Dipogon are probably opportunists, attacking whatever spiders they encounter while searching tree trunks, but the collective prey records for the genus are rich in crab spiders (family Thomisidae, especially the genus Xysticus). Other spiders known to be prey include jumping spiders (Salticidae) and ground spiders (Gnaphosidae). There is at least one record of a hacklemesh weaver, genus Amaurobius, as prey for D. calipterus calipterus.

Prey is stung into deep paralysis, or perhaps killed outright, by the female wasp. She carries her victim by grabbing the spinnerets at the tip of the abdomen and walking sideways or backwards, dragging the limp spider in the process.

It is suspected that the female wasp finds a suitable nesting site before she begins hunting. Nests are in typically in pre-existing, tubular cavities such as the abandoned tunnels of wood-boring beetles, or the soft pith in dead or broken plant stems such as sumac. Pre-drilled wood nest blocks put out for solitary bees may be used by these wasps. The linear cavity is divided into cells. After a spider is stored in the first, bottom-most cell, the wasp lays an egg on it and then builds a curtain of mud and/or other material that serves as the ceiling of that cell and the floor of the next cell.

The conglomerate nature of the cell partitions and closing plug is rather unique and helpful in identifying the nests of these wasps. Besides mud, particles of leaves, insect body parts, and even caterpillar frass (poop) may be incorporated into the nest partitions and closures. The female wasp uses the “beard” of hairs on her maxillary palps to carry such material back to the nest. The hairy palps are the only sure way to identify the genus Dipogon, but they are seldom visible on live specimens in the field.

Keep an eye out for these ant-mimicking wasps, even in your own backyard. Yes, it may take looking at a lot of tree trunks, or foliage, but you will eventually be rewarded with at least a glimpse of these unique pompilids.

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.
Krombein, Karl V., Paul D. Hurd, Jr., David R. Smith, and B.D. Burks (eds). 1979. Catalog of Hymenoptera in America North of Mexico vol. 2, Apocrita (Aculeata). Washington, DC: Smithsonian Institution Press. Pp. 1199-2209.
Townes, Henry. 1957. “Nearctic Wasps of the Subfamilies Pepsinae and Ceropalinae,” Bull. U.S. Natl. Mus. 209: 1-286.

Priocnemis minorata

One of the more conspicuous wasps of springtime in deciduous forests of the eastern United States is the spider wasp Priocnemis minorata. Indeed, it is usually the first member of the family Pompilidae to be seen. You can find them right now, as I did in Missouri last week.

These are medium-sized insects, the length of the front wing varying from 6-12 millimeters, the entire insect a bit longer. Their long legs make them appear even larger overall. They are shiny black in color, with the wings having a smoky and/or iridescent appearance. Note the serrated top surface of the tibia (“shin” segment) on the hind leg. This character immediately sets them apart from other black spider wasps you are likely to encounter. Look for them hunting among leaf litter in places where there is dappled sunlight through the tree canopy. The wasps are active from late March to mid-June, with peak activity in April and May.

While this species is most abundant in the U.S. east of the 100th meridian, it has also been recorded from the Pacific Northwest in southeast British Columbia and western Oregon. Additional Canadian records include Nova Scotia, Quebec, and Ontario.

Priocnemis minorata is a generalist predator of spiders, and probably an opportunist. Known host records include Coras juvenilis, Wadotes calcaratus, Wadotes hybridus (hacklemesh weavers, family Amaurobiidae), Hibana gracilis (ghost spiders, family Anyphaenidae), Clubiona obesa (sac spiders, family Clubionidae), Dolomedes tenebrosus (fishing spiders, family Pisauridae), Trochosa terricola, Gladicosa gulosa, Arctosa rubicunda, and Varacosa avara (wolf spiders, family Lycosidae).

Last week I found the female specimen shown here at The Inn on Crescent Lake in Excelsior Springs, Kansas, that oddly persisted in staying in one place. Eventually, I figured out that she was in the process of carting off a paralyzed, immature nursery web spider, Pisaurina mira (family Pisauridae). It turns out this is not a new host record, as this spider species was discovered as a host for Priocnemis minorata previously (Kurczewski, et al., 1987).

Dick Walton has captured some stunning video of this species in action, including what might be a new host record: a running crab spider in the genus Thanatus (family Philodromidae). He also shows another specimen dispatching a wolf spider.

The female wasp digs a burrow prior to going hunting. The entrance is usually hidden under dead, dry leaves. The tunnel itself is vertical or slightly angled, and may reach a depth of 27.5 centimeters. One cell is constructed at the bottom of the shaft, with as many as six other cells branching off progressively from the bottom up. One spider is apparently stored in each cell, on its side, with an egg laid on the spider’s abdomen. The egg hatches in two days and the larva that hatches matures in about a week. The remainder of the year is spent in the pupa stage, until the adult wasp emerges the following spring.

When I lived in Cincinnati, Ohio, I could always tell when spring had really arrived by when the spider wasps were out. I encourage you to look for this species in your own neck of the woods, among the trilliums, violets, and other wildflowers on the forest floor.

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. and Edmund J. and Roy A. Norton. 1987. “New Prey Records for Species of Nearctic Pompilidae (Hymenoptera),” J. Kans. Entomol. Soc. 60(3): 467-475.
Townes, Henry. 1957. “Nearctic Wasps of the Subfamilies Pepsinae and Ceropalinae,” US Nat. Mus. Bull. No. 209. 286 pp.

Wasp Wednesday: Anoplius aethiops

The western states may have the giant “tarantula hawks,” but most of the U.S. and adjacent Canada has another fierce spider wasp in the family Pompilidae. On our trip to Cape May, New Jersey, September 30-October 5, we encountered several big females of Anoplius aethiops. Ok, they were most likely that species, but it requires microscopic examination to separate them from the similar Anoplius cleora.

The first one I saw was so large that I at first mistook it for a Great Black Wasp, a wasp in an entirely different family. Both wasps are large, jet black, with black wings that reflect blue or violet. The spider wasps do not, however, have the abdomen separated from the thorax by a thin petiole (stalk). When I got a side view of the wasp, it became clear it was not in the genus Sphex. Still, it goes to show how difficult it is to identify insects in the field.

Female Anoplius aethiops measure 13-23 millimeters in body length, males 9-18 millimeters. Though black in color, their bodies reflect a hint of bluish or purplish color in the right light.

My “Spider Sunday” post was about a species of large wolf spider, the kind that these big spider wasps target. Each female Anoplius aethiops digs her own burrow, usually originating inside an existing burrow or crevice, and then goes off to find a spider to stash inside the tunnel. Heidi and I encountered one female wasp toting a good-sized wolf spider down the path we were on in Cape May Point State Park.

The wasp was walking backwards quite rapidly, while using her jaws to hoist her heavy prey completely off the ground. This feat of strength would be like you or me lifting a recliner with our teeth and backing across the street.

The spider is not even dead, but only paralyzed by the wasp’s venom when she stung it in a nerve center. Unfortunately, even in my rather careful efforts to get more images of wasp and spider, she ended up abandoning her prize. An abandoned, paralyzed spider may or may not eventually “come to” from its comatose state.

All known host spiders for Anoplius aethiops are lycosid wolf spiders: Hogna helluo, H. carolinensis, H. aspersa, H. baltimoriana, H. frondicola, Rabidosa santrita, Gladicosa gulosa, and Schizocosa ocreata. Once she places a spider in the bottom of her underground nest, the wasp lays a single egg on the spider, exits, and then closes the burrow. She will repeat the process as long as she is able. This is a wasp most common in late summer, and persisting into late fall. Most of the specimens we saw in New Jersey had tattered wings, indicating they had been active for quite some time already.

Look for Anoplius aethiops in open areas like fields, forest edges, meadows, and prairies. It tends to be replaced by A. cleora in open sand dune habitats. Both genders visit flowers such as wild carrot, goldenrod, sweet clover, milkweed, and throughwort for nectar. Anoplius cleora rarely visits flowers, so that is another way to distinguish the two species.

This wasp ranges coast to coast in the United States, save for North Dakota, plus southern British Columbia and southeast Canada to the north; and Mexico and Guatemala to the south. It is apparently less common in the southeast U.S. than in other parts of its range. Late July through mid-September is the typical seasonal range for this wasp.

Sources: Evans, Howard E. 1951. “A Taxonomic Study of the Nearctic Spider Wasps Belonging to the Tribe Pompilini (Hymenoptera: Pompilidae) Part II: Genus Anoplius Dufour,” Trans Am Entomol Soc LXXVI, 207-361.
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.
Kurczewski, Frank E. and Edmund J. and Roy A. Norton. 1987. “New Prey Records for Species of Nearctic Pompilidae (Hymenoptera),” J Kans Entomol Soc 60(3): 467-475.
Wasbauer, M.S. and L.S. Kimsey. 1985. “California Spider Wasps of the Subfamily Pompilinae (Hymenoptera: Pompilidae),” Bulletin of the California Insect Survey vol. 26, 130 pp.

Wasp Wednesday: Poecilopompilus algidus

Here is a wasp that is still a wasp, but probably not the wasp you think it is. Did that make any sense? I know the first time I saw the spider wasp Poecilopompilus algidus, I thought it was a paper wasp (genus Polistes in the family Vespidae). Mimicry is not always a case of some defenseless organism looking and acting like a venomous, poisonous, or otherwise potentially dangerous animal.

Müllerian mimicry describes instances in which two or more species that are capable of defending themselves share a similar “look,” especially in color and pattern. Müllerian mimicry is named for German naturalist Fritz Müller, who first recognized this widespread survival tactic. Many well-armed species sport bold markings known as “aposematic” or “warning” colors.

I can attest from personal experience that Poecilopompilus spider wasps can back up their advertisement. The only specimen I collected of P. interruptus, in Cincinnati, Ohio, gave me a sting to remember! Ironically, the only other sting I recall with more vividness was from a Polistes aurifer paper wasp that I got when I was a careless child.

Poecilopompilus is a mostly tropical genus with only three representative species that reach the United States (P. flavopictus is recorded only in extreme southern Texas).

I just learned something new in researching this article. P. algidus has a much more widespread distribution in the U.S. than I had previously thought. It occurs from California to Arizona, Utah, Texas, Florida, and north to South Dakota, Minnesota and Michigan, even Massachusetts. Even more amazing, its mimicry is quite “plastic.” While in the south it tends to resemble a large paper wasp, in the north it may masquerade as another spider wasp in the genus Anoplius: Almost completely black with red bands on the top of the abdomen, as in this specimen. Not surprisingly, this insect is divided into at least four subspecies. The one I’ve imaged here is P. algidus coquilletti.

One cannot reliably use color patterns to even separate this species from P. interruptus, and equally widespread member of the genus. They key characters to look at instead are the spines on the front tarsi (“feet”) of females, and the inner margin of the eyes.

Species	spines on front tarsi	inner eye margin
P. algidus	3 strong spines	strongly convergent at top
P. interruptus	4 weak spines	parallel at top

The biology of these spider wasps is not especially well-known, though all are thought to prey exclusively upon orbweaver spiders in the family Araneidae. I have personally observed a female Poecilopompilus transporting a Western Spotted Orbweaver, Neoscona oaxacensis down a road in southern Arizona. My friend Margarethe Brummermann was able to document it here.

The female wasp stings her victim into weak paralysis and then hauls it backwards overland to a suitable nesting spot in bare soil. There she will deposit her burden, often in the crotch of a grass tussock or other vegetation, and begin excavating a shallow burrow. She may bite her way through hard soil, then kick the resulting crumbs beneath here with her front legs. The tunnels made by P. interruptus vary from 2.5 to eleven centimeters deep, angling from 45 to 90 degrees. The density of the soil might have an effect on depth. At the bottom is a spherical chamber where the prey is placed and a single egg laid upon it. Great care is then taken in filling and concealing the burrow entrance, the better to discourage potential parasites and predators.

One is most likely to see members of the genus Poecilopompilus on flowers, or on extrafloral nectaries of sunflower (Helianthus spp.). They are conspicuous insects in size as well as color, females of P. algidus coquilletti varying from 15-20 mm in body length, males 13-17 mm.

Sources: Evans, Howard E. 1949. “A taxonomic study of the nearctic spider wasps belonging to the tribe Pompilini (Hymenoptera: Pompilidae) Part I,” Trans Am Entomol Soc, vol. 75, no. 3/4: 133-270.
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. 1981. “Observations on the nesting behavior of spider-wasps in southern Florida (Hymenoptera: Pompilidae),” Fla Entomol, vol. 64, no. 3: 424-437.
Wasbauer, M. S. and L. S. Kimsey. 1985. “California Spider Wasps of the Subfamily Pompilinae (Hymenoptera: Pompilidae),” Bulletin of the California Insect Survey, vol. 26: 1-130.