Spider identity

Asked June 11, 2016, 4:51 PM EDT

Can you confirm what species this is?

Douglas County Kansas

1 Response

Thank you for your question. This appears to be a male brown recluse spider. The male reproductive organs, or palps, the two appendages with the swollen bulb-like ends, are visible in front of the spider's head.

The violin-shaped marking on the cephalothorax is present on most brown recluses, as it is on your specimen. However, this is not always the case, In young and recently molted spiders, the pigment that makes up the marking may be very faint. Some species of brown recluse never have much pigment in this area, so the marking is never very pronounced. It does not appear that the spider in your photograph has any prominent spines on its legs. Brown recluse spiders' legs have very fine hairs, but no obvious spines.

The most critical factor in determining if a spider is a brown recluse is not visible in your photograph, and that is the number and placement of the spider's eyes. Most spiders have eight eyes. The brown recluse has six, and they are arranged in a very distinct pattern. If there is adequate light, and you can see the front and top portion of the head, you can see the number and placement of the eyes. Without being able to confirm the number of eyes and their placement, I can't be positive that this is a brown recluse, but the rest of the characteristics, and the fact that this species is common in the eastern part of Kansas, lead me to believe that it is.

The brown recluse spider is considered to pose a significant health risk to humans. Usually, bites from this spider do not result in severe symptoms. In about 10% of the cases, necrotic tissue lesions develop that may require skin grafts. In North America, fewer than 1% of cases involve a systemic reaction, usually in children, that can be fatal if not properly diagnosed and treated.

For more information on the brown recluse see:

https://en.wikipedia.org/wiki/Brown_recluse_spider
http://spiders.ucr.edu/recluseid.html
https://www.bookstore.ksre.ksu.edu/pubs/MF3133.pdf

An excellent book you may want to read is:
Vetter, Ricard S. (2015). The Brown Recluse Spider. Ithaca: Cornell University Press

Hope this information helps, and thank you for using Ask an Expert.

Jim