I eventually figured out this is called a "windscorpion" or sometimes a "sunspider". A web search will turn up more than you care to know (including movies of these things in action). These two links are worth checking out, too, if you want to see some beautifully evil creations of nature:

http://wrbu.si.edu/www/stockwell/photos/p_marginemaculatus.jpg
http://wrbu.si.edu/www/stockwell/photos/amplypygid(hon).jpg

(For scale, that's a large pill bug with it.)

Brandyn Webb / brandyn@sifter.org