File:Latrodectus mactans.jpg

Latrodectus mactans (Family Theridiidae ) Fatal bites from Latrodectus spiders seldom occur in the case of healthy adults. The ratio of body weight to venom volume is critical. Bites to body parts with extremely good vascular supply, such as the penis, can result in the venom being distributed throughout the body before body defenses can be mobilized, so adult fatalities usually occur to males in areas that still use sit-down outdoor toilets.

From

(NASA)