Black Widow Spiders
Facts, Identification & Control
Black widows are identified by red hourglass marking on the underside of their abdomens. Black widows are shiny black in color. Most black widow spiders’ bodies are 3 to 10 mm in size. Females are larger than males and can measure 13 mm in body length. These spiders are members of the genus Latrodectus.
Behavior, Diet & Habits
Where Are Black Widow Spiders Found?
Black widow spiders favor dark, secluded areas such as crevices and woodpiles. Inside the home, black widows typically hide in sheltered, dimly lit locations such as garages, dark corners, basements, closets and cluttered areas. They thrive primarily in temperate zones and are known to be abundant in the American South.
Several species of Latrodectus or “widow” spiders are present in North America. The most common are: the southern widow (Latrodectus mactans) found in the American South and Northeast; Latrodectus hesperus found in the west; the brown widow (Latrodectus geometricus) found in the South; and the northern widow (Latrodectus variolus) found in the Northeast.
An important characteristic of the black widow spider is its comb foot. This row of strong, curved bristles is located upon the hind pair of legs and is used to pitch silk over captured prey.
Black widows are shy in nature. They are solitary, socializing only during copulation. Black widows are nocturnal and spin webs during daytime. They can sometimes be seen hanging upside down in their web, exposing a telltale hourglass abdominal marking. This marking is bright red and signals danger to predators and attackers.
Male vs. Female
On average, male black widow spiders are smaller than females, reaching only about half their size in length. However, the legs of the male black widow are considerably longer in proportion to the female’s and are marked by orange and brown at the joints. Males may exhibit red and white stripes on the abdomen depending on the species and are more colorful and finely patterned than females.
Diet / Prey: What Do Black Widows Eat?
Like most spiders, the food source of the black widow spider includes a variety of arthropods, including ants, caterpillars, grasshoppers, beetles, cockroaches and scorpions, among others.
Black widows process their food outside of their bodies. After prey is caught in the web, it is injected with digestive enzymes. They consume the prey after it has softened and liquefied. Following feeding, the abdomen of the spider’s body expands as its stomach fills. Like most spiders, the black widow is capable of living for several months without food. Some specimens have been known to survive almost one year in the absence of prey.
Black Widow Webs
Black widows are the largest of web-spinning spiders. Read more about the black widow’s web.
Life Cycle / Reproduction
Black widow mating occurs in springtime into early summer. In some cases, black widow females consume males after mating, feeding on them as sources of nutrients needed for egg fertilization. Female black widow spiders can produce several egg sacs in summer months. These sacs are tightly woven, silken cups and are protected fiercely by the female until they hatch.
Egg sacs are white, tan or gray in color, have a paper-like texture, and measure 12 to 15 mm in diameter. They may be pear-shaped or globular. Each egg sac contains hundreds of eggs, from which hundreds of spiderlings emerge. However, only a handful of these young survive, as black widows are cannibalistic during the early stages of their lives.
Black widow spider eggs can be found in dark crevices beneath stones and in natural debris such as woodpiles. Barns and other secondary buildings are likely to host these spiders, as well. Black widow spider eggs may also be deposited within neglected materials or animal and rodent nests.
Surviving spiderlings undergo molting stages known as instars. Many spiderlings overwinter as immatures, and then they mature fully the following spring. Spiderlings are white and orange in color and resemble adult black widow males. Females turn black as they grow older. Black widow spiderlings are cannibalistic and consume other spiderlings from their brood for nutrients.
Surviving hatchlings leave the web within a few days, at which point they experience ballooning. During the ballooning process, black widow spiderlings release strands of silk into the air and are carried to new locations. Black widow spiderlings then begin to spin their own webs and capture their own food. Spiderlings find a hiding place to survive in the winter. When warm weather returns, they finish developing into adults.
Although the expected lifespan of black widow spiders is one year, some specimens have been known to live up three years. These spiders live longest in captivity.
Signs of a Black Widow
Black widows produce messy, irregular webs. Webs usually are located near ground level and under a protected ledge such as under lawn furniture or wood piles. The female with the iconic red hourglass marking also indicates their presence.
In North America, black widows are most common in the southern United States. These areas are more suitable for their life cycles and activities. Black widows prefer dry and dark locations and will seek warm dwellings in winter. However, specimens have been found as far north as Canada. Worldwide, widow species can be found on almost every continent.
Northern Black Widow
As designated by its name, the northern black widow spider (Latrodectus various) is found primarily in the Northeast United States. They may live as far south as Florida, as far north as Canada and as far west as Texas.
Species of widow spiders are also occasionally transported in shipments of household goods to states outside of their natural range. Northern black widows are primarily found in marginal land habitats with sparse vegetation, stumps, hollow logs and piles of debris. Northern black widow spiders are rarely found indoors. However, they may enter human dwellings on piles of firewood or other items brought inside. Most adult female northern black widow spiders are shiny black in color, with rows of red spots atop the abdomen. Crosswise bars that resemble a red hourglass appear on the underside of the abdomen.
Southern Black Widow
The weather in the American South is extremely conducive to the development of black widow spiders, and several species can be found. A great example is the southern black widow spider (Latrodectus mactans). They are one of the most common black widow species in the Southern United States. Females spin irregular and nonsymmetrical webs. They do not prefer to venture indoors but can be found in garages or basements near openings to the outdoors such as around garage doors.
Like the northern black widow, the female southern black widow spider is jet-black in color and is shiny. They also have a red hourglass-shaped mark on the underside which serves to identify it.
How the Black Widow Spider Received its Name
The black widow spider received its name due to a story about its mating behaviors. Courtship begins when males go out in search of receptive females. Upon approaching a web-spinning female, the male spider will wait for an indication of her willingness: females interested in mating remain still, allowing males to inseminate them.
As the story goes, following insemination, female black widow spiders kill and feed upon their mates. This story led to the black widow’s name. However, it is a misconception that all female black widows kill and consume their mates. Rather, this behavior is typically only observed in captivity.
The black widow contributes to the balance of the ecosystem by consuming insects such as flies and mosquitoes. It also controls crop pest populations, feeding on pests that defoliate plants, including locusts, grasshoppers, beetles and caterpillars.