Black widow spider, Latrodectus mactans

Body size

Female to 16mm; male to 5mm.


The highly venomous black widow spider has an unmistakable appearance. About the size of a finger-nail, the female is satin-black and usually has a bright red 'hour-glass' marking on the underside (photo). The pale-coloured male is much smaller and does not bite.

Habitat, range and season

Buildings, plantations, rubbish dumps and stony places. Southern USA and Mexico. Adults occur at various seasons depending on location.


A tangle-web with taut threads bearing sticky globules.

Bite reports

In general terms, local pain develops 5 minutes to an hour after the bite. The development of systemic effects caused by the neurotoxin is variable but usually involves muscle cramps, spasms, and sweating. Pain in the stomach area can be excruciating but most patients recover within 24-72 hours (many references, e.g. Bates, 2001).

UK spider bites