Spider Sign

By: Filip Tkaczyk

There are cannibals living in the shed. The bodies of their victims lay sprawled on the floor, legs akimbo. Bodies drained of their insides. I would have not noticed them in the gloom of that space because they are very small. I would not have noticed, that is, if it were not for the white, liquid scat one of them left on the brake handle of my bicycle. Little dots the size of pin-heads speckling the black paint. The scats also spattered the plastic floor of the shed, between the spent bodies and below these creatures silken homes. 

Here is the scat of the American house spider (Parasteatoda tepidariorum) and the carcasses of giant house spiders (Tegenaria duellica) who were her meals.

Who are these cannibals, you might ask? Well, they are Parasteatoda tepidariorum. More commonly referred to as the "American house spider." All the ones I could see in the shed were females, as was visible by their bulbous abdomens.

Here is a female American house spider with her prey, a yellow bear caterpillar.

You share your spaces with spiders. It is not a matter of keeping a clean house. Even the cleanest houses have spiders in them, at least as part-time residents. One of those is the American house spider, who is a member of the Cobweb weavers or Comb-footed spiders (Theridiidae). This family includes the most famous and perhaps some of the most feared spiders on the North American continent, the black widows (Steatoda ssp.). The American house spiders do not possess the kind of potentially dangerous venom of their more famous relatives and are harmless to humans.

These spiders are shy, unobtrusive and silent neighbors. They are also excellent predators of the very large, fast running funnel web weavers (Tegenaria ssp.) which often invade houses at certain times of the year. The victims of our American house spider are most likely to be the wandering male funnel web weavers, as they go out in late summer and early fall looking for females of their own species. One of the species in this funnel web weaver group - the hobo spider (Tegenaria agrestis) - has been falsely accused of being a dangerous species with a bite that causes necrotic wounds. There is little evidence to support this, however, and as its name "agrestis" implies, it has long been a common part of agricultural/rural areas of Europe. It is not considered a species of concern in Europe.

Here is the old, tattered web of a giant house spider (Tegenaria duellica).

In several of the webs in and around the shed where the gray-to-tan, tear-drop shaped, papery silken purses which are the distinct egg sacs of our American house spiders. Most of them still looked plump and full. I found one female closely tending her egg sacs. You can see her in the image below. Notice the egg sac on the far left is shriveled and there are a few tiny young out of focus in the background.

In another females web, a tight cluster of tiny young can be seen. They cling tightly to the silk and rest after just hatching out. Notice the line of liquid silk droplets on the far right. These may have been added to this nursery web to give it extra tensile strength and flexibility.

How big are these little guys and their egg sacs? Well, here is the tip of my finger for scale.

The tracks and sign of the invertebrate world has really been getting my attention lately. You cannot take a step outside without being next to or on top of some kind of invertebrate sign. Though scary to some, I find spiders especially fascinating. I am very grateful to people like Noah Charney and Charley Eiseman - authors of Tracks & Sign of Insects and Other Invertebrates - for bringing my attention, and the general attention of the tracking community at large to the wealth of this kind of sign.

Enjoy looking for the tracks of those wonderful mammals, birds , reptiles and amphibians, but don't ignore the little guys all around you!

Hope you enjoyed this read. More to come soon!