When people picture black widow spiders, they picture the shiny black female with a red hourglass. The male black widow looks very different: he is far smaller, often brownish, purplish or grey rather than black, and usually has red or red and white marks on the top of his abdomen instead of an hourglass underneath.
The black widow male is also harmless to people. Only bites from female widow spiders are dangerous to humans. A male’s adult life is short and has one main purpose: finding a female and mating without being eaten.
Male black widow: key facts
- Size: body length 3 to 6 mm (0.12 to 0.24 in) in the southern black widow, compared with 8 to 13 mm (0.31 to 0.51 in) for the female
- Color: often purplish, brownish or grey, similar to a juvenile, rather than glossy black
- Markings: red, or red and white, stripes, bars or spots on the upper side of the abdomen; no bold hourglass like the female
- Lifespan: about three to four months for a male southern black widow; females can live up to three years
- Danger to humans: none; only female widow spider bites are dangerous
- Cannibalism: females sometimes eat males, but much of the evidence comes from lab cages where males could not escape
- Genus: Latrodectus, the widow spiders, with 34 species worldwide
Sources: Wikipedia: Latrodectus mactans and Wikipedia: Latrodectus.
How to identify a male black widow
Male black widows are easy to overlook. Their bodies are only a fraction of the female’s size, although their legs are long in proportion to the body. Researchers often compare an adult male to the size of a grain of rice.
Instead of the female’s glossy black, males are usually lighter, and in the southern black widow they are either purple or look much like juveniles. Juveniles are greyish to black with white stripes and yellow and orange spots, so young spiders of both sexes are easy to confuse with adult males.
The clearest sign is the pattern. Male widow spiders often have red, or red and white, markings on the upper side of the abdomen, ranging from a single stripe to bars or spots. The famous red hourglass is a feature of the female’s underside.
Male vs female black widow
- Size: females 8 to 13 mm body length; males 3 to 6 mm
- Color: females shiny black; males lighter, often purplish, brown or grey
- Markings: females have a red hourglass underneath; males have red or red and white marks on top
- Abdomen: females have a large, round abdomen for producing eggs; males are slim
- Lifespan: females up to three years; males a few months
- Bite: female bites can cause latrodectism; male bites are not dangerous to humans
Life cycle of a male black widow
Black widows hatch from eggs in a round silk egg sac. A female southern black widow can make four to nine egg sacs in one summer, each with about 100 to 400 eggs, and the eggs take about 20 to 30 days to hatch. Few of the spiderlings survive, as many are lost to cannibalism, lack of food and lack of shelter.
Young males molt several times as they grow. Black widows can be mature enough to breed after two to four months.
According to arachnologist Catherine Scott, quoted by KQED, juvenile males have their own webs, but after their final molt they abandon them and go looking for females.
How male black widows find a mate
Female black widows stay in their webs and lace their silk with pheromones that attract males. Researchers say a male can detect this scent from about 200 feet away. The scent carries information about the female, including her mating history and how hungry she is.
Male black widows tend to choose females that have already eaten, which lowers the risk of being mistaken for food. Research reported in 2019 also found that males can follow the silk trails of rival males to reach females faster.
Courtship and web reduction
When he reaches a female’s web, the male has to signal that he is a suitor and not prey. He does this by making specific vibrations on the web with his abdomen.
He then does something surprising: he takes her web apart. In a behavior called web reduction, the male cuts the web down strand by strand, bunches the silk into a ball and wraps it in his own silk. Scientists think this masks the female’s scent and keeps rival males away. Females in these studies were less aggressive and ready to mate sooner when males reduced their webs.
Before mating, the male drapes fine strands of his own silk over the female’s legs, sometimes called a bridal veil.
Mating
Before he goes looking for a female, a mature male spins a small sperm web, deposits sperm on it and loads it into his palpal bulbs, the paired organs at the front of his body. During mating he inserts these palps into the female’s reproductive openings.
Do female black widows really eat the males?
Sometimes, but much less often than the name suggests. Sexual cannibalism gave widow spiders their common name, yet females of some species only rarely eat males, and much of the evidence was collected in laboratory cages where the male had no way to escape.
In the wild, a careful male that approaches a well-fed female often mates and leaves alive. In the western black widow, a female that eats a male is usually treating him as a meal because she is hungry. The species where males are regularly eaten are different: in the Australian redback and the brown widow, the male flips his body toward the female’s mouth during mating.
Is a male black widow venomous or dangerous?
All widow spiders produce venom containing latrotoxin, which acts on the nervous system and causes the condition called latrodectism. Female widow spiders have unusually large venom glands, and only the bites of females are dangerous to humans. A male black widow bite is not a medical concern for people.
Even female bites are rarely fatal. In the United States about 2,500 people report a black widow bite each year, and most do not need medical treatment. Black widows are not aggressive and usually bite only in defense, when they are accidentally squeezed or pinched against the skin. Anyone who has severe muscle pain, cramps or sweating after a spider bite should get medical care.
Webs and silk
Black widows build three-dimensional, tangled cobwebs from very strong silk, not the neat round orb webs of garden spiders. Weight for weight, spider silk is stronger than steel wire, because steel is about six times as dense as silk.
Adult males do not build capture webs of their own. They spend their short adult lives moving between webs in search of females.
What do black widows eat?
Black widows mainly eat insects, but they also take woodlice, millipedes, centipedes and other arachnids that blunder into the web. When prey gets tangled, the spider rushes out, wraps it in silk and bites it. Its venom takes about ten minutes to work, and digestive enzymes then liquefy the prey.
Where black widows live
In North America there are three main black widow species: the southern black widow (Latrodectus mactans), found mostly in the southeastern United States north to Ohio and west to Texas; the northern black widow (Latrodectus variolus); and the western black widow (Latrodectus hesperus). Black widows are active around dusk and at night and like sheltered, dark spots such as inside pipes and under porches.
Living with black widows
- Wear gloves when moving firewood, stones or stored boxes
- Shake out shoes, gloves and clothing left in garages or sheds
- Clear clutter and seal gaps where spiders can shelter
- Leave the small, pale males alone; they pose no risk to people
Frequently asked questions
What does a male black widow look like?
A male black widow is small, with a body only 3 to 6 mm long and long legs. He is usually purplish, brownish or grey rather than black, with red or red and white stripes or spots on top of the abdomen.
Do male black widows have a red hourglass?
Not a bold one like the female. The red hourglass on the underside is a female feature. Males usually show red, or red and white, markings on the upper side of the abdomen instead.
Can a male black widow bite you?
Only the bites of female widow spiders are dangerous to humans. Males are small and spend their adult lives searching for mates, and their bite is not considered a medical risk.
How long does a male black widow live?
A male southern black widow lives about three to four months, while a female can live up to three years.
Does the female always eat the male after mating?
No. Many males mate and leave alive, especially when they approach a female that has already eaten. Much of the evidence for cannibalism comes from lab cages where males could not escape.