Masters of Mud: Auplopus Spider Wasps

The first image in this post is not of the insect I will be discussing today. That is because I am far more frequently asked what these little mud barrels are, and what makes them. Indeed, you are more apt to stumble upon these nests than you are to see their maker. While most spider wasps in the family Pompilidae dig burrows for their nests, or exploit pre-existing cavities, those in the genus Auplopus create free-standing mud cells.

I have few images of these wasps, and detest “stealing” images from others for my posts even though I give full credit when I do, so I hadn’t done an entry about Auplopus until now. It took a Facebook post by Eileen Miller to remind me that I was overdue to address them. Eileen was kind enough to share her own images in exchange for learning more about the wasps and their nests.

© Eileen Miller

There are ten recognized species of Auplopus in North America, but the genus is in dire need of revision. Collectively, the genus occurs across the entire continent. One species, A. carbonarius, is introduced from western Europe, and has been documented in New York and Michigan, but probably has a wider distribution in the U.S. than is currently known.

Several species are bright metallic blue-green, and the females at least are basically inseparable externally. Males can be identified by differences in the genitalia. Auplopus are small, averaging about 10 millimeters in length. Females have an oval spot on top of the abdomen near the tip called a “pygidial plate” that they use like a masonry trowel to manipulate mud pellets into segments of their mud nests. The female curls her abdomen beneath her during such work, so that the pygidial plate can contact the mud.

© Yurika Alexander via Bugguide.net Auplopus mellipes female

The nests are usually constructed inside pre-existing cavities in wood, or at least in sheltered niches such as under bark on standing trees, crevices in rock walls, or even inside the abandoned nests of other wasps like Sceliphron caementarium (Black and Yellow Mud Dauber), Trypoxylon politum (the Pipe Organ Mud Dauber), and paper wasps (Polistes spp.). The tiny barrel-shaped cells are roughly 15 millimeters in length and 7-10 millimeters wide, often stacked end-to-end, two to five per row.

Nest inside hole where a bolt used to be

The wasps appear to be mostly opportunistic hunters of spiders that do not spin webs.

Documented prey includes spiders from thirteen different families: Crab spiders (Thomisidae), jumping spiders (Salticidae), sac spiders (Clubionidae), ground sac spiders (Trachelas sp. in Corinnidae), ghost spiders (Anyphaenidae), longlegged sac spiders (Cheiracanthium sp. in Miturgidae), ground spiders (Gnaphosidae), nursery web spiders (Pisauridae) being the usual victims of North American Auplopus.

© Marie L. Schmidt via Bugguide.net Female wasp with spider prey

Adult or immature spiders may be taken, and the wasps usually amputate several, if not all, the legs of their prey. This allows the wasp to feed on the blood of the spider, but also facilitates easier transport of the victim over the ground. Presumably, more than one spider is placed in each mud cell before the female lays an egg on the last victim and then seals the cell.

© Eileen Miller, inside of cell showing pupa in cocoon

In at least one species, the emerging adult wasp regurgitates liquid to soften the mud cap on its cell, allowing it to more easily chew its way to freedom.

Auplopus seldom visit flowers, but can often be found around aphid colonies on honeyvine milkweed (Ampelamus albidus, Cynanchum leave), sunflower, and other plants. They feed on “honeydew,” the sweet liquid waste products that aphids secrete.

© Eileen Miller

Look for these little wasps from May to October, but especially July through September when they are most abundant. It should be noted that other Hymenoptera make very similar mud nests, particularly some of the Osmia mason bees, and some mason wasps (family Vespidae, subfamily Eumeninae). Auplopus are surprisingly well-studied insects, but information is scattered over articles in many different scientific journals and books.

Sources: Eiseman, Charley and Noah Charney. 2010. Tracks & Signs of Insects and Other Invertebrates. Mechanicsburg, Pennsylvania: Stackpole Books. 582 pp.
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): 66-119.
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press (Publication 4670). 570 pp.
Kurczewski, Frank E. 1989. “Observations on the Nesting Behavior of Auplopus caerulescens subcorticalis and Other Auplopodini (Hymenoptera: Pompilidae),” Gt. Lakes Entomol. 22(2): 71-74.
Kurczewski, Frank E. and Mark F. O’Brien. 1991. “Auplopus carbonarius, a Palearctic Spider Wasp, Extends its Range to Michigan (Hymenoptera: Pompilidae),” Gt. Lakes Entomol. 24(3): 185-186.
O/Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, New York: Comstock Publishing Associates (Cornell University Press). 406 pp.

A Nursery Web Spider, Pisaurina dubia

Spiders can be very confusing to identify. There is a great deal of “convergent evolution” in appearance and behavior between very different genera, even families. I found myself momentarily wrong earlier this month when a lanky, striped spider wandered onto the sheet of our blacklight setup in a suburban neighborhood in Manhattan, Kansas. It was the first time I had seen a specimen of Pisaurina dubia, a type of nursery web spider in the family Pisauridae.

Note pale second leg on right, regenerated after being lost previously

Most members of the Pisauridae are large or very large when mature, but those in the genus Pisaurina spend the winter as sub-adults, so they are slightly smaller in size in the spring. Consequently, I mistook this one for another kind of spider. This spider measured only about 12-15 millimeters in body length, so my initial identification was one of the slender crab spiders in the genus Tibellus, family Philodromidae.

Tibellus slender crab spider

The “habitat” where the spider was prowling was a lawn, which is also rather atypical for nursery web spiders that favor much taller grass at the least, and usually shrubs and trees, too. Mature females construct “nursery webs” amid foliage at least a few inches off the ground where they suspend their egg sac just prior to the emergence of the spiderlings. Mom guards the youngsters until they molt again and disperse.

Turns out that a lawn is not foreign territory after all, at least not for this species. P. dubia also occurs in the litter and understory of woods, along forest edges, in barns on hay bales (well, one specimen anyway), and on the exterior of homes, sometimes straying indoors (Guarisco, 1994). This spider has even been found living in pitcher plants, climbing around on Spanish moss (actually a type of bromeliad), in sugarcane fields, and low vegetation in wetlands in the southeast U.S.

© Jon P. Inghram via Bugguide.net

To my knowledge, this species has no common name, but I might suggest it be called the “Horned Nursery Web Spider” or “Tufted Nursery Web Spider.” One of the distinguishing features of Pisaurina dubia appears to be a central tuft of hair that usually projects from between the eyes at the front of the cephalothorax like a tiny horn (see image above).

This species ranges across the southern two-thirds of the eastern U.S. from New Jersey to Florida, and east to eastern Nebraska, Kansas, Oklahoma, and Texas.

Sources: Balaban, John and Jane, et al. 2005. “Species Pisaurina dubia,” Bugguide.net
Carico, James E. 1972. “The Nearctic Spider Genus Pisaurina (Pisauridae),” Psyche 79: 295-310.
Guarisco, Hank. 1994. “Natural History Observations of the Spider, Pisaurina dubia (Hentz) (Araneae: Pisauridae) in Northeastern Kansas,” Trans. Kans. Acad. Sci. 97(3-4): 149-152

Long-legged Flies

Happy “Fly Day Friday,” everyone. Long-legged flies in the family Dolichopodidae include those little, bright metallic green flies you see darting over leaves in sunny spots; but they also include flies that run up and down tree trunks, or skate across the surface of puddles. The diversity of this family is almost as staggering as the Syrphidae, Bombyliidae, and other fly families that are more familiar.

The Condylostylus species imaged above, from Skokie, Illinois, is the typical dolichopodid we normally see in the garden, along forest edges, and similar habitats. Like all longlegged flies they are predatory on other small insects. It can be maddeningly difficult to get a good image of one because the flies aren’t that large to begin with, hardly ever stop moving, and can be sensitive to the pre-flash on your camera such that you wind up with either an empty frame, or an out-of-focus fly in mid-air as it departs.

Condylostylus sp. with prey

Dolichopodids range in size from barely one millimeter to “giants” of ten millimeters. Most are five millimeters or less. They are usually metallic green, copper, or bronze, though many species are muted rather than brilliant.

Hydrophorus sp. pair, Colorado Springs

What is truly astounding is the diversity of this family. There are nearly sixty (60) genera in North America north of Mexico, with about 1,300 species. It is difficult enough to identify a given specimen to genus, but species ID generally requires examining the male genitalia. Not that the male’s “man parts” are not obvious. His claspers and other, um, paraphernalia are easily seen as forward-protruding appendages at the tip of the abdomen (curled beneath the abdomen).

The front “feet” (tarsi) of males of most Dolichopus species are adorned with special scales that may resemble tiny flags. These ornaments are used to display to females in complex courtship dances.

Hydrophorus sp., Pueblo Reservoir, Colorado

Besides looking for these flies on foliage, keep an eye out for them on the water, too. Hydrophorus species skate across the surface of puddles, intermittent streams, and near the shores of lakes and reservoirs where they behave much like water striders. Members of the shorter-legged genus Dolichopus can also be seen on the surface film. The adults of these flies are even adept at preying on mosquito larvae, nabbing the “wrigglers” when they ascend for air.

Liancalus genualis, South Deerfield, Massachusetts

Longlegged flies do not have beak-like mouthparts like robber flies or dance flies, but instead have a lower “lip” modified into an extendable appendage and equipped with a pair of flaring, opposable lobes that can crush a victim or tear it to pieces. Hard to believe these diminutive, delicate insects are really quite vicious predators.

The “woodpecker” flies in the genus Medetera are commonly seen on the trunks of trees, literally standing on tiptoe in a seemingly awkward posture. They still have the agility of their cousins, I assure you.

Medetera sp., Redondo Beach, California

As far as is known, dolichopodid maggots are also predatory. Most are aquatic or semi-aquatic, but the larvae of at least some Medetera species roam the galleries of bark beetles, feeding on the beetle grubs. The larvae of most species, however, remain a mystery.

It is impossible to do justice to these remarkable flies in a blog post, or even a book, but I encourage you to do a double-take the next time you see an unfamiliar little fly. It may well be a dolichopodid, and what you observe could easily yield new knowledge.

Tachytrechus angustipennis(?), Colorado Springs

Sources: Bartlett, Troy, et al. 2004. “Family Dolichopodidae – Longlegged Flies,” Bugguide.net
Marshall, Stephen A. 2006. Insects: Their Natural History and Diversity. Richmond Hill, Ontario: Firefly Books Ltd. 732 pp.
McAlpine, J.F., B.V. Peterson, G.E. Shewell, H.J. Teskey, J.R. Vockeroth, and D.M. Wood (coordinators). 1981. Manual of Nearctic Diptera Volume 1. Ottawa: Agriculture Canada. 674 pp.

The Black Corsair

Turn on an outdoor light anywhere in the eastern U.S. at night at this time of year and you are likely to attract one, if not several, individual males of the assassin bug known as the “Black Corsair,” Melanolestes picipes. Why only males? More on that in a moment. What are they doing there? They are likely looking for other insects to prey upon.

This species exhibits what is called sexual dimorphism. Adult males are fully winged and are strong fliers. Females usually lack hind wings and have the front wings reduced to mere pads, though there are exceptions. They are nocturnal, like the males, hiding under stones, boards, and other objects by day.

Female M. picipes, Taney County, Missouri

This is among one of the most abundant assassin bugs in the United States, found from New England to Florida, and west to Colorado, Utah, and California. It is often confused with the Masked Hunter, but the Black Corsair averages smaller, at 15-20 millimeters in body length.

Most specimens from the northern part of its range are wholly jet black, but southern specimens may have a red or orange edge to the abdomen, or even have the abdomen entirely red. Those specimens are sometimes confused with the bordered plant bugs I wrote about last week. The red-bordered forms of Melanolestes picipes were formerly considered a separate species, M. abdominalis. The two are now recognized as a single species.

Male M. picipes, Taney County, Missouri

A highly distinctive feature of these agile assassin bugs are the “ankle weights” or “leg-warmers” they seem to be wearing on the first and second pair of legs, at the distal end of the tibial (“shin”) segment. The inflated attribute is called the fossula spongiosa, a pad composed of a dense mat of hairs, with pores beneath them that exude a thin film of oil to the flared tips of the hairs. The whole affair allows the bug to chase prey over slick substrates, cling to struggling victims, and grip a mate in the case of males.

M. picipes from Cape May, New Jersey, after a bad molt

Be careful that you don’t ever mindlessly swat one of these insects if it lands on you. The defensive bites of assassin bugs in general are excruciating, and the odds of being bitten go up when the Black Corsair comes to town. Because they are attracted to lights, and run and fly with great speed and agility, the males may find their way indoors.

It is just this scenario that played out in the notorious “kissing bug scare” in the summer of 1899 in the eastern United States. Accounts vary, some stating the panic began with a single incident of a woman being bitten in Washington, DC (Freiberg, et al, 1984); others claiming there really was a higher incidence of bites from bugs that year. That sensationalized newspaper reporting helped fan the flames of paranoia is a subject of unanimous agreement. Whether the assassin bug responsible was the Black Corsair, or the Masked Hunter, neither species would have been lusting after human victims, simply looking for insect prey in the wrong places.

Male M. picipes, Manhattan, Kansas

Sources: Berenbaum, May. 2009. “Kiss and telmophage,” Am. Entomol.. 55(2): 68-69, 112
Freiberg, Marcos and Jerry G. Walls. 1984. The World of Venomous Animals. London: T. F. H. Publication, Inc. Ltd. 191 pp.
McPherson, J.E., S.L. Keffer, and S.J. Taylor. 1991. “Taxonomic Status of Melanolestes picipes and M. abdominalis (Heteroptera: Reduviidae),” Fla. Entomol. 74(3): 396-403
Slater, J.A. and R.M. Baranowski. 1978. How to Know the True Bugs. Dubuque, Iowa: Wm. C. Brown Company Publishers. 256 pp.