Honestly, it may take a quiz show and the willingness of the participants (spiders in this case) to help identify the right species of sac spider. The native sac spider (Cheiracanthium inclusum) is very similar to the one introduced from Europe in 1978 (Cheiracanthium mildei). In the picture from my yard I believe I have the latter on my hand, but I am not 100% sure, not even close…
Sac spiders can be found walking about on foliage; under leaf litter, stones, and boards; on buildings under the windowsills and siding; and in our homes. This individual was found resting on a house plant I have outside on the deck in the summer. It was not there when I put the plant outside, so it did not migrate to the outdoors.
Both species are of similar size (females 5 to 10 millimeters; males 4 to 8 millimeters) and coloration. Apparently Cheiracanthium inclusum is a light yellow to cream color with dark brown jaws (chelicerae), tips of the tarsi, and palps. Cheiracanthium mildei has a slightly greenish tinge to its abdomen and a pale yellow cephalothorax. The chelicerae, tarsi, and palps are similar to those of Cheiracanthium inclusum . Both spiders have a slightly darker dorsal stripe running lengthwise down the abdomen. Confused yet? I may need a microscope to really know what I am dealing with here.
In general, sac spider retreats may be found outdoors under objects or indoors. They build hide-outs which are simple silken tubes or sacs in which the spiders hide during the daytime. In homes with light, neutral-colored walls and ceilings, the retreats may go unnoticed, as they are small and blend in with the background coloration.
Who am I? Cheiracanthium inclusum or Cheiracanthium mildei?
The agrarian sac spiders deposit their eggs in June or July. The eggs are loosely deposited within a silken sac, and the female remains nearby to guard them. Cheiracanthium inclusum is more often encountered outside and they deposit their eggs on the undersides of leaves. Cheiracanthium mildei is found more often within human-made structures and deposits almost exclusively indoors. These spiders actively hunt for prey rather than capturing it within a web. Often these spiders encounter humans and bite when they become trapped between a person’s skin and sheets or clothing. These two species of Cheiracanthium account for a significant number of human bites. Although these bites are painful, they normally do not result in anything serious.
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