Zebra Jumper

Last Monday, my wife and I went out to the Rocky Mountain Arsenal National Wildlife Refuge northeast of Denver. We were pleased to find a handful of specimens of the cute little “Zebra Jumper,” Salticus scenicus, family Salticidae. These wonderful jumping spiders should be abundant here, as they seem to be in most other parts of the U.S. and southern Canada, but we don’t seem to see many.

These are small spiders, adult females measuring only 4-7 millimeters in body length, males 4-6 millimeters, but their bold color pattern makes them relatively conspicuous anyway. They also like to prowl walls of buildings, fenceposts, and other vertical man-made objects. Indeed, they seem most common in urban and suburban settings where people are likely to notice them.

Adult male

Adult males and females can be easily separated from each other. Females have a more mottled appearance, the black-and-white pattern broken by streaks of beige or tan. Males are almost exclusively black and white; and they have greatly elongated chelicerae (jaws) with correspondingly long and impressive fangs. Apparently they use these massive body parts to duel with each other when competing for mates. Flaring their jaws and opening their fangs, they interlock with their adversary much like a pair of bull elk.

It is suspected that the Zebra Jumper is native to Eurasia, but has now spread across the temperate areas of the globe thanks to human commerce and travel.

Just about any insect or spider the same size as a Zebra Jumper, or smaller, is fair game. I once watched one stalk and kill a surprisingly large “greenbottle” blow fly (Lucilia sp., family Calliphoridae), on a wall in Cincinnati, Ohio. It slowly walked around the fly until it got directly behind the insect. I watched as it wiggled its abdomen, presumably laying down a launching pad of silk to anchor the ever-present dragline these spiders spin as a safety measure should they miss an intended target when leaping. The spider then leaped onto the back of the fly, pinning its wings in a way that prevented the fly from taking to the air. In a matter of a minute or so, it was all over for the fly.

Look for these charismatic arachnids on almost any vertical surface outdoors. They occasionally stray indoors, too. Mature specimens are common from April through October, males appearing earlier than females. Mating takes place early in the season, with spiderlings growing during the summer months. Subadult specimens overwinter in protected niches.

Here in the United States, Salticus scenicus ranges across the northern tier of states, south to southern California, Colorado, northern Texas, Ohio, and North Carolina.

Jumping spiders in general are very alert, with the best eyesight of any terrestrial invertebrate. They cock their heads (technically the cephalothorax) in the direction of anything that interests them. This curiosity is sometimes interpreted as aggression by the casual human observer, but these are not dangerous spiders. Enjoy their engaging personalities.

Sources: Adams, R.J. 2014. Field Guide to the Spiders of California and the Pacific Coast States. Berkeley: University of California Press. 303 pp.
Bradley, Richard A. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.
Buddle, Chris. 2012. “Salticus scenicus: a fashionable urban spider,” Arthropod Ecology, McGill University
Howe, Amanda, and Eric R. Eaton. 2014. “Salticus scenicus (Zebra Jumper),” Spiders.us.

March Flies in May

You cannot judge the seasons by the calendar, apparently. Here in Colorado we have march flies, family Bibionidae, emerging in mid-May. Members of the genus Bibio are among the more locally-abundant dipterans one is likely to see in the spring across most of North America.

Bibio sp. male, Colorado

Ironically, April and May seem to be the months when one is most likely to see these flies. Adults range from roughly 6-12 millimeters or so, but it is not their size that usually gets your attention. It is their sheer numbers. Males gather in swarms that can blanket the ground and low vegetation. Females are attracted to the party and select mates in the frenzy of fly bodies.

Bibio sp. swarm,Colorado © Jeannie Mitchell

It is easy to tell males from females. Females are almost literally “pinheads,” with tiny heads for the size of their bodies. Males, on the other hand, have large, spherical heads composed almost entirely of two compound eyes. Those eyes are referred to as “holoptic” when they meet at the top of the head.

BibioMarch flies are most easily separated from similar flies (if there really are any similar dipterans) by the presence of a pair of stout, downcurved spurs at the end of the tibia segment on the first leg. These spurs are used by the female to dig down into the soil several inches where she will deposit her eggs in masses of 200-300. There are not many fossorial (digging) flies in the U.S. and Canada.

Bibio sp. female, Massachusetts

Precious little is known about the biology and life cycle of march flies, but those larval stages that are known feed mostly on decaying matter in rich soils. They also feed in manure and compost, and on the roots of grasses and herbs. On occasion they can be serious pests of cereal crops, vegetables, and rangeland grasses. The mature larvae probably overwinter, pupating in the early spring.

There were at one time 53 species of Bibio recognized in North America north of Mexico, but since then several species have been synonymized (“lumped”), and we stand at about 37 species currently. Many former “species” were separated on the basis of leg color, density of hair, and other characteristics that vary greatly within a single species. Real differences exist in characters of the male genitalia, but who wants to dissect that?

Dilophus sp. female, California

Dilophus sp. male, California

The genus Dilophus is very similar to Bibio, but instead of long spurs on the front legs, they have a ring of shorter teeth. These flies are usually less robust, and smaller, than Bibio, too. Plus, they are frequently reddish in color rather than black. There are 15-18 species north of Mexico.

Lastly, the infamous “lovebugs” in the genus Plecia, with two species found principally along the Atlantic and Gulf coast states, are abundant in spring and fall. They are named for their habit of flying in copula, frequently colliding with vehicles and generally making a nuisance of themselves to humans. Perhaps we are jealous because they can remain conjoined for two or three days. Hey, when you only live two or three days as an adult fly, what better way to spend your time?

Bibio sp. pair, Colorado

Sources: Coin, Patrick, et al. 2004. “Family Bibionidae – March Flies,” Bugguide.net
Fitzgerald, Scott J. 1997. “Additional Notes on Nearctic Bibio Geoffroy (Diptera: Bibionidae),” Proc. Entomol. Soc. Wash. 99(2): 294-304).
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 vol. 1. Ottowa: Agriculture Canada. 674 pp..

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