Sunday, October 28, 2012

Spider Sunday: Burrowing Wolf Spider

The story behind any given spider image can be quite interesting, and usually teaches the photographer a thing or two. I could not bring this one to you without the help of a number of individuals. The outcome is that I have finally seen a burrowing wolf spider in the genus Geolycosa. Is he not a handsome spider?

I was out with Heidi and some of our mutual friends on a geocaching adventure in the vicinity of Widefield and Security, just southeast of Colorado Springs in El Paso County on Monday, October 22. We stopped to find one cache at a particularly ugly ravine that was obviously used as a dump site. I won’t tell you about the surprising pieces of trash, but one member of our party, walking ahead of me, stopped, looking down, and called out to me. She had found a large spider crossing her path and was kind enough to point it out.

I recognized it as a wolf spider (family Lycosidae), and suspected it was a species in the genus Hogna. It seemed a little small, though. I took many pictures, few of which turned out to my satisfaction, but reviewing them I determined this was a mature male specimen, and it didn’t obviously fit anywhere in the genus Hogna. There is considerable variability in color and markings from one individual to the next, though, so I remained open-minded.

As luck would have it, it is “Arachtober” on, a group that accepts submissions of arachnid images only during the month of October each year. I posted my best image of the wolf spider and expressed my reservations about my identification. Another group member (and personal friend), Lynette Schimming, commented on my image and suggested it might actually be a male burrowing wolf spider, Geolycosa missouriensis. She included this link that shows a couple images of a male of that species. So, I have one Dan L. Johnson to thank now, too. Such is the circuitous route that spider identifications can take.

At least one of my references calls Geolycosa missouriensis the “Missouri Earth Spider.” Another lists it as the “Missouri Wolf Spider.” Indeed, the epicenter of its range is the Great Plains, from southern Canada to Texas, east to New York and west to Utah and Arizona. Like all members of the genus Geolycosa, it spends the majority of its life inside a deep burrow.

These are large spiders. Mature females measure about 21 millimeters, males 15-18 millimeters in body length. A sprawling male can span 34 millimeters. The front legs are stout, built to aid in digging, though most excavation is done with the powerful jaws (chelicerae). The front of the cephalothorax is much higher than the rear portion, which easily separates this genus from other wolf spiders.

Geolycosa missouriensis apparently has at least a two year life cycle, with half-grown individuals overwintering in burrows that may be a meter or more in depth (summer burrows average 20-25 centimeters). The vertical shafts are lined with silk, and enlarged as the spider grows. The mouth of the burrow may be ringed with a turret of silk mixed with debris.

Both genders mature in late summer or early autumn, and mating takes place at this time. Hence, the wandering male we found was likely looking for a spider spouse. Mated females lay their eggs in May or June of the following year. Each female prepares a spherical egg sac like other wolf spiders, and suns the parcel at the mouth of her burrow on warm days. Spiderlings do not disperse very far from their maternal home, so populations tend to be localized, and not easy to detect.

I may return to the area where we found this male sometime next year to look for the burrows of females. They prefer sandy soil in open areas with sparse litter that they incorporate into the turrets of their burrows. I hope I am lucky enough to encounter more of these charismatic arachnids no matter what the location.

Sources: Bercha, R. and R. Leech. 2011. “Geolycosa missouriensis,” Spiders of Alberta.
Evans, Arthur V. 2008. National Wildlife Federation Field Guide to Insects and Spiders of North America. New York: Sterling Publishing Co., Inc. 497 pp.
Fitch, Henry S. 1963. Spiders of the University of Kansas Natural History Reservation and Rockefeller Experimental Tract. Lawrence: University of Kansas. 202 pp.
Kaston, B.J. 1978. How to Know the Spiders (Third Ed.). Dubuque, IA: Wm. C. Brown Company Publishers. 272 pp.

1 comment:

  1. Very Cool! He is indeed a handsome spider, with such a charismatic face.


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