A giant water bug:

If you want to know more, this blog has an interesting account: http://somethingscrawlinginmyhair.co...ant-water-bug/
Also, here: http://nathistoc.bio.uci.edu/hemipt/Toebiter.htm , and here: http://dermatology.cdlib.org/DOJvol4...rus/letho.html

Like many types of water bugs, they can fly. So, if you have a hospitable body of water, they are likely to visit. Many water bugs can bite or sting, but bugs are notable for the high level of pain they can inflict.