Latrodectus hesperus, the Western black widow spider or Western widow, is a venomous spider species found in western regions of the United States of America. The female's body is 14–16 millimeters in length and is black, often with an hourglass shaped red mark on the lower abdomen. This "hourglass" mark can be yellow, and on rare occasions, white. The male of the species is around half this size and generally a tan color with lighter striping on the abdomen. The population was previously described as a subspecies of Latrodectus mactans and it is closely related to the northern species Latrodectus variolus. The species, as with others of the genus, build irregular webs.

The female's consumption of the male after courtship, a cannibalistic and suicidal behaviour observed in Latrodectus hasseltii (Australia's redback), is rare in this species. Male Western widows may breed several times during their relatively short lifespans.

The ultimate strength and other physical properties of Latrodectus hesperus silk were found to be similar to the properties of silk from orb weaving spiders that had been tested in other studies. The ultimate strength for the three kinds of silk measured in the Blackledge study was about 1000 MPa. The ultimate strength reported in a previous study for Nephila edulis was 1290 MPa ± 160 MPa