The genus Latrodectus, commonly known as widow spiders, is recognized by the adult female’s glossy black body and vibrant red hourglass marking on the underside of its abdomen. This striking coloration is a classic example of aposematism, a warning signal to predators. However, relying solely on this characteristic for identification is misleading. Many widow spiders, including males, juveniles, and related species, deviate entirely from the iconic black and red pattern. Natural variations influenced by age, sex, and species mean that many individuals of the genus Latrodectus do not have any red markings.
Variations in Markings Based on Sex and Age
The classic red hourglass is primarily a feature of the mature female in North American black widow species, such as the Southern Black Widow (L. mactans) and the Western Black Widow (L. hesperus). Males and young spiders of these species appear drastically different, which is the most common reason a widow spider lacks the expected red mark.
Male black widows are physically much smaller than females, often measuring about half the size. Their coloration is typically light brown, tan, or gray, lacking the female’s solid, glossy black body. If a marking is present on the underside, it is usually pale yellow, white, or faint orange, not vivid red.
Juvenile spiders exhibit a completely different appearance as they pass through various developmental stages (instars). Young spiders are often pale, sometimes white or yellowish, with distinct striping or spotting on the dorsal (upper) side of the abdomen. These markings are complex patterns of white, yellow, and orange-red stripes or dots. The solid black coloration and complete red hourglass only emerge as the female nears maturity. The male retains this lighter, patterned coloration throughout its short adult life.
Other Widow Species That Naturally Lack Red
Beyond variations within a single species, the Latrodectus genus includes species whose adult females naturally lack the “black and red” pattern. The Brown Widow (Latrodectus geometricus), for instance, is increasingly common and presents distinct characteristics.
The Brown Widow’s base color ranges from light tan or beige to dark brown, and its abdomen often has a mottled or geometric pattern of black and white. While it possesses an hourglass marking on its underside, the color is typically vivid yellow or yellowish-orange rather than deep red. This lighter coloration and dorsal patterning distinguish it from its black-bodied relatives.
The Red Widow (Latrodectus bishopi), found mainly in Florida scrub habitats, also lacks the traditional black-and-red pattern. The female Red Widow has a reddish-orange cephalothorax and legs, but its abdomen is blackish, often marked with a row of red or orange dots bordered by yellow. Its underside may feature only one or two small, separated red marks, or a broken triangle, instead of the classic connected hourglass shape.
Key Identification Features When Red Is Absent
When the red hourglass is absent, identification relies on structural and behavioral characteristics common to the entire Latrodectus genus. All widow spiders possess a noticeably large, bulbous, or globular abdomen relative to the rest of their body. The overall body is smooth and shiny.
The characteristic web is a reliable indicator of a widow spider’s presence. They construct a distinctive, irregular, three-dimensional tangle web, often described as messy, typically built in sheltered, dark locations near the ground. This web is made of strong, non-spiral silk threads.
A defining feature of all members of the Theridiidae family (widow spiders) is the presence of a comb-like row of serrated bristles (setae) on the tarsus (foot) of the hind legs. This “comb foot” is used to quickly wrap and throw silk over ensnared prey, distinguishing them from many other spider families. While this feature requires magnification, the combination of the globular body, the irregular web structure, and the spider’s habitat provides practical field identification.