Prairie Dog Spider

Prairie dog towns are known to provide habitat for many species of plants and animals.  Some of those are attractive and/or popular wildlife species like burrowing owls and ferruginous hawks.  Others are attractive (at least to me), but maybe less popular among the general public, including prairie rattlesnakes and black widow spiders.  It’s easy to understand why rattlesnakes would appreciate the availability of burrows.  The snakes can sun themselves on the bare soil at the edge of a burrow, but quickly retreat underground to cool off or escape predation.  From the perspective of spiders, I’m sure the burrows funnel insects nicely into webs, but I’m not sure why prairie dog burrows are so attractive to black widows in particular.  I’ve spent a fair amount of time looking for invertebrates around Nebraska, but prairie dog towns are the only places I’ve ever seen black widows.

A black widow spider in an abandoned prairie dog burrow.

A southern black widow spider (Latrodectus mactans) in an abandoned prairie dog burrow.  The Nature Conservancy’s Niobrara Valley Preserve, Nebraska.  The spider, including spread legs, was only slightly larger than a nickel.

While I was up along the Niobrara River last week, I walked around a small prairie dog town hoping to find either rattlesnakes or black widows to photograph.  I didn’t find any snakes, but did find black widows in two of the first 20 or so burrows I examined.  Both had webs strung across abandoned burrows.  That makes sense, but I wonder if the spiders recognize the burrows as abandoned before they build a web?  If not, I imagine there are some pretty interesting prairie dog/spider interactions as prairie dogs burst in or out of burrows and encounter the webs.  I laughed about something similar with badgers and spiders about a month ago, but the more potent venom in black widow spiders adds an extra degree of risk to prairie dogs…  My guess is that very few, if any, prairie dogs are actually harmed by black widows (the spiders probably just try to get away and prairie dog fur seems thick enough to protect against the small fangs anyway) but I don’t know of any research that’s actually investigated that.

My camera set-up for the above spider photo.

My camera set-up for the above spider photo.

Once I found the two black widow spiders, the next challenge was figuring out how to photograph them.  The first issue was that the late afternoon sunlight was very bright and the tunnels were very dark, making the lighting conditions problematic.  A homemade collapseable diffuser (thin fabric sewed to a plastic hoop) helped cut the light intensity.  The second problem was that the angle of the webs relative to the shape of the burrow made it difficult to get the spider in focus.  I finally gave up trying to find a position from which to photograph the first spider and concentrated on the second.

However, the biggest issue was that the spiders were very tuned in to movement near the edge of the burrow and kept scurrying away into the shadows every time my head, camera, or hand moved across the opening.  The above photo took 45 minutes to obtain.  Most of that time was spent waiting for the spider to return to the web (and the light) every time I re-positioned the camera, focused, or breathed (or so it seemed).  It’s not a fantastic shot, but given the challenging situation it still feels like a kind of victory.

Photo of the Week – March 18, 2011

Plains pocket gophers are often underrated in terms of their impact on prairies.  Prairie dogs get all kinds of attention because they stand at the edge of their burrows and make cute little sounds (they also get negative attention because they compete with cattle for forage).  I would argue that pocket gophers have a similar degree of impact on their surroundings, and they’re in many more prairies than prairie dogs,but they get much less attention because they’re less visible.

The mounds from a pocket gopher's feeding tunnel are exposed after a spring prescribed fire. It'd difficult to tell whether the tunnel was made the previous fall or during the winter. The Nature Conservancy's Platte River Prairies - Nebraska.

The majority of pocket gopher tunnels are within a foot of the surface.  Gophers feed on the roots of plants as they tunnel – mainly tap roots of wildflowers.  Besides the impacts they have on plants from their feeding behavior, their mounds also have an impact on prairie plant communities.  There is contradictory evidence about whether or not the mound creation provides space for new plants (thus increasing plant diversity) or removes plants and allows strong perennials to expand into the disturbed soil of the mounds (thus decreasing plant diversity), but most studies – especially in mixed-grass prairies have found an increase in diversity.

Many thanks to The Nature Conservancy’s Jim Luchsinger for help interpreting the photo and providing background information on pocket gophers.