They occur throughout all 4 deserts of the American Southwest.
All widows are venomous.
The species L. hesperus is common in the western US and is the Black Widow found in the North American deserts. Still, it is a venomous creature, and must be taken care of with respect. It is found throughout the world's tropical regions, has been introduced into southern Texas and central and southern Florida. The Red-back is found in all parts of Australia except in the hottest deserts and on the coldest mountains. The female Black Widow is shiny black, usually with a reddish hourglass shape on the underside of her spherical abdomen.