Dimorphic Jumping Spider, Maevia inclemens

When I lived in Ohio I had the great honor of being introduced to Dr. George Uetz at the University of Cincinnati. At the time he had a graduate student, Dave Clark, who was doing research on the courtship behavior of the Dimorphic Jumping Spider, Maevia inclemens. Ever since then I have had a special place in my heart for this unique member of the Salticidae.

"Tufted form" male, Missouri

What makes this spider so special, you ask? The name says it all. The male of this species comes in two distinct forms: a "tufted form" that is all-black with white legs; and a "gray form" with black pinstripes and orange spots and chevrons. Not only do they look like separate species, but they behave like two different spiders, too. Each male performs a complex dance that is different from that of the other form.

"Tufted form" male, Indiana

The tufted form, named for the triple-Mohawk style hairdo, literally stands on tiptoe, dips his abdomen, and waves his front pair of legs overhead at a prospective mate. The gray form takes a "low rider" position and sidles back and forth.

"Gray form" male, Kansas

Dave Clark capitalized on those differences, as well as his expertise in video, and created animations of a tufted form male doing a gray form dance, and vice versa. He then played his mixed-up dance mix in front of live female spiders. Jumping spiders have better eyesight than any other terrestrial invertebrate, so they could actually watch, and react to, the videos on a monitor. This was back in the late 1980s, so Dave dubbed his lab "MTV" for "Maevia Television."

"Gray form" male, Kansas

The Dimorphic Jumper is a species commonly encountered in the eastern half of the U.S. where it prowls understory foliage, climbs on walls and fences, and occasionally enters homes. These are not overly large spiders, males ranging from 4.8-7.0 millimeters in body length, females 6.5-10 millimeters. Females have consistent markings, being mostly pale with a pair of orange or red racing stripes running down the back of the abdomen.

The first time I saw a tufted form male of this species, it was on a sidewalk in Cincinnati and I initially mistook it for a carpenter ant. This species is not generally considered an ant mimic, but considering that carpenter ants forage in the same places as Maevia, it is not out of the question I suppose.

Juvenile female or gray form male, Massachusetts

So what was the result of those experiments? The dance of the black form male is apparently more successful at attracting the attention of a female from a greater distance, while the dance of the gray form male is better at wooing a lady spider closer to him. You can see videos here on YouTube of both kinds of males performing. There is no word on whether the females presented with the wrong combo of male appearance and dance moves suffered psychological damage.

"Is there a female down there?"

Sources: Bradley, Richard A. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.
Clark, David L. and George W. Uetz. 1993. "Signal efficacy and the evolution of male dimorphism in the jumping spider, Maevia inclemens," Proc. Natl. Acad. Sci. USA 90: 11954-11957.
Guarisco, Hank, Bruce Cutler, and Kenneth E. Kinman. 2001. "Checklist of Kansas Jumping Spiders [illustrated]," Kansas School Naturalist 47(1).
Moffett, Mark W. 1991. "All Eyes on Jumping Spiders," Nat. Geo. Mag. 180(3): 42-63.

Pantropical Jumping Spider

This week, if you live pretty much anywhere north of Mexico, a tropical vacation sounds pretty appealing. Well, if you were a Pantropical Jumping Spider, Plexippus paykulli, you would probably be enjoying yourself right now. This species is a world traveler, now dispersed to most tropical and subtropical climates across the globe. Envious?

Male

The Pantropical Jumper is pretty easy to find, too, since it hangs out on the exterior of buildings where it can be quite conspicuous. The only problem might be telling it apart from the Gray Wall Jumper which is often seen on buildings, too. Both species are of similar size. Adult females of the Pantropical Jumper are 10-12 millimeters in body length; males average 9.5 millimeters.

Female

Plexippus paykulli is also sexually dimorphic, meaning that the male gender looks radically different from the female sex. In fact, it would be easy to assume they are two different species. This is typical of many jumping spiders: the males are adorned with colorful scales, or tufts of hair on their legs and/or pedipalps which are used to communicate with the female through elaborate displays, often accompanied by vibrations carried through the substrate (surface on which the spiders are sitting).

Male

Pantropical jumpers don’t sit on the beach sipping fruity drinks. Nope. They actively seek prey by day, including small moths, flies, flying ants, and even other spiders. They have the typical behavior of most jumping spiders in the family Salticidae, running a short distance, pausing, pumping their pedipalps up and down, and turning to face whatever piques their curiosity (or perceived threat).

Mated females of this species spin a small, flat egg sac about nine millimeters in diameter that contains anywhere from 35-60 eggs. A larger silken envelope, 25-35 millimeters around, covers the egg case and serves as a retreat for the female to guard her future offspring. Look for these nurseries under eaves of buildings, in cracks and crevices, or under boards and other objects.

Female

Here in the United States, Plexippus paykulli can be found year-round in South Carolina, Georgia, Florida, the Gulf Coast states, and south Texas. Outlying populations in New Mexico, and north along the Atlantic seaboard are probably the result of accidental introductions. You are also likely to see this spider in such exotic locales as Hawaii, Hong Kong, India, Greece, and parts of Africa. It is assumed that the species is native to southeast Asia.

The Pantropical Jumping Spider should be considered an asset to any resort, hotel, or motel, for they are literally a mobile pest control service. They are known to hunt mosquitoes and small cockroaches among other pests. I guess you would call that a “working vacation.”

Male

Sources: Bradley, Richard A. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.Edwards, G.B., Jr. 2002. “Jumping Spiders,” Featured Creatures. Division of Plant Industry and University of Florida.
Gaddy, L.L. 2009. Spiders of the Carolinas. Duluth, MN: Kollath+Stensaas Publishing. 208 pp.
”Pantropical Jumper,” iNaturalist.

Wasp Wednesday: Wasps in Love

It seems the theme lately has been insect sex. Seriously, I don’t think I’ve ever seen and photographed so many f*ing “bugs” (literally!) as I have in the past week or two. Wasps have been no exception. It is one of those behaviors for which they tend to sit still for a change. It is also a situation in which you can finally tell the subtle differences between the genders (or not so subtle differences in some cases).

Take the example of the pair of Ammophila thread-waisted wasps shown above. The male is the one on top. The tip of his abdomen is rather blunt, and that he is deploying his, um, “hardware.” The female doesn’t seem to like this very much, though. Notice how her abdomen tapers to a point.

One may logically ask how can mating take place when a female wasp has a stinger. Wouldn’t that hurt the male? How can he get his sperm into such a small, sharp opening? Well, the stinger is not involved in copulation. In the evolution of wasps, the egg-laying organ (ovipositor) has in some cases become modified into a retractable stinger that is now used to paralyze prey, and as a weapon of last resort in self-defense. The female’s sex organs are located near the same opening from which the stinger is thrust, but again, the stinger does not participate in mating activities.

While the sexes are very similar in most kinds of wasps, this is not always the case. Above we have a pair of pollen wasps, Pseudomasaris vespoides, the male attempting to court a female that has her head stuck inside a Penstemon flower. Many male wasps are, shall we say….opportunistic in this way. To his credit, he is petting his potential mate, tapping his “chin” on her back. I wish I had video to demonstrate that, but I don’t. The male is larger than the female, with various hooks and other external anatomical features on his abdomen that help him latch onto his mate. Pseudomasaris males also have much longer antennae than the females, terminating in segments that form a club. She has clubbed antennae, too, just much shorter.

Male wasps may have other body parts modified as well. Males of crabronid wasps in the genus Astata have enormous eyes that meet at the top of their heads: all the better to see passing females as he sits atop an elevated perch. He will also chase off competing males.

Above is a male wasp in the genus Crabro. He has the tibial segment of his front leg modified into a broad shield. Scientists speculate that these plates function in displaying to females and other males, and/or as stimulation to the female during courtship. The shields glisten in the sun, reflecting light brightly and perhaps disclosing the location of the perched male to passing females and competing males. During courtship, the male perches atop the female and covers her eyes with his shields. The shields are translucent and create patterns of light perceived by the female (Low and Wcislo, 1992).

There is much competition among males for available females. This was made graphically clear to me earlier this week when I received an image from someone via AllExperts.com, asking me “what behavior is going on here?” The picture showed three male Black and Yellow Mud Daubers, Sceliphron caementarium, stacked on top of a single female. Well, two of the males were stacked on each other, actually.

Females of Eremnophila aureonotata, a thread-waisted wasp, don’t let mating keep them from other activities. The pair shown below is resting, but “engaged” pairs can often be seen flitting from flower to flower just like single wasps. This species is common throughout the eastern U.S. and adjacent southern Canada, so keep a lookout for tandem couples.

In the interest of maintaining my current followers, and in the hopes of recruiting still more, I shall refrain from any comparisons between wasps and Homo sapiens when it comes to sex. I encourage voyeuristic behavior only when it comes to watching insects and arachnids, thank you.

Sources: Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World: A Generic Revision. Berkeley: University of California Press. 695 pp.
Low, Bobbi S. and William T. Wcislo. 1992. “Male Foretibial Plates and Mating in Crabro cribellifer (Packard) (Hymenoptera: Sphecidae) With a Survey of Expanded Male Forelegs in Apoidea,” Ann. Entomol. Soc. Am. 85(2): 219-223.

The Saga Concludes

Like I haven’t written enough already about the brown-banded cockroach (see All Grown Up and The “University Roach”), along comes another chapter.

I was visiting the insect collection in the Department of Entomology at the University of Arizona in Tucson yesterday, when in the process of moving a cart to get to a cabinet, I discovered a cockroach, belly-up on the floor. I could tell it was a brown-banded roach even before I turned it over. I had seen another dead one here before (before I had a camera). The neat thing about this one was that it was a male.

Oddly, I have never seen a living adult male of this species. Then again, until I saw live ones at the University of Massachusetts, I had not seen a living example of either gender. I suspect they are less populous than other “domestic” roaches, and maybe more secretive, too.

In any event, Supella longipalpa is an outstanding example of sexual dimorphism in the order Blattodea. While the females are broad-bodied with shortened forewings (called tegmena), males are more slender, with long tegmena and fully-functional hindwings as well.

Other cockroach species have even more dramatic differences between the sexes, males being fully winged and females totally wingless. The sand roaches in the genus Arenivaga come to mind. They occur here in the Arizona outdoors, so maybe I’ll eventually be able to share their story here on my blog as well. For now, though, I can close the book on the brown-bandeds.