The prevalence of sexual cannibalism, a behaviour in which the female eats the male after mating, has inspired the common name "widow spiders".
This behaviour may promote the survival odds of the offspring; however, females of some species only rarely show this behaviour, and much of the documented evidence for sexual cannibalism has been observed in laboratory cages where the males could not escape.
Male black widow spiders tend to select their mates by determining if the female has eaten already to avoid being eaten themselves.
They are able to tell if the female has fed by sensing chemicals in the web.

Like other members of the Theridiidae, widow spiders construct a web of irregular, tangled, sticky silken fibres.
Black widow spiders prefer to nest near the ground in dark and undisturbed areas, usually in small holes produced by animals, or around construction openings or wood piles.
Indoor nests are in dark, undisturbed places such as under desks or furniture or in a basement.
The spider frequently hangs upside down near the centre of its web and waits for insects to blunder in and get stuck.
Then, before the insect can extricate itself, the spider rushes over to envenomate and wrap it in silk.
To feed, the spider's mouth pulses digestive juices over the prey, which liquifies—and then the spider internalizes by capillary action, sucking the slurry into its mouth.
Their prey consists of small insects such as flies, mosquitoes, grasshoppers, beetles, and caterpillars.
If the spider perceives a threat, it quickly lets itself down to the ground on a safety line of silk.

As with other web-weavers, these spiders have very poor eyesight and depend on vibrations reaching them through their webs to find trapped prey or warn them of larger threats.
When a widow spider is trapped, it is unlikely to bite, preferring to play dead or flick silk at the potential threat; bites occur when they cannot escape.
Many injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched.
The blue mud dauber (Chalybion californicum) is a wasp that, in western North America, is the primary predator of black widow spiders.

The ultimate tensile strength and other physical properties of Latrodectus hesperus (western black widow) silk are similar to the properties of silk from orb-weaving spiders that had been tested in other studies.
The tensile strength for the three kinds of silk measured in the Blackledge study was about 1,000 MPa.
The ultimate strength reported in a previous study for Trichonephila edulis was 1,290 ± 160 MPa.
The tensile strength of spider silk is comparable to that of steel wire of the same thickness.
However, as the density of steel is about six times that of silk, silk is correspondingly stronger than steel wire of the same weight.

Spiders of the genus Steatoda (also of the Theridiidae) are often mistaken for widow spiders, and are known as "false widow spiders"; while their bite can be painful, they are significantly less harmful to humans.
The prevalence of sexual cannibalism, a behaviour in which the female eats the male after mating, has inspired the common name "widow spiders". This behaviour may promote the survival odds of the offspring; however, females of some species only rarely show this behaviour, and much of the documented evidence for sexual cannibalism has been observed in laboratory cages where the males could not escape. Male black widow spiders tend to select their mates by determining if the female has eaten already to avoid being eaten themselves. They are able to tell if the female has fed by sensing chemicals in the web.
Like other members of the Theridiidae, widow spiders construct a web of irregular, tangled, sticky silken fibres. Black widow spiders prefer to nest near the ground in dark and undisturbed areas, usually in small holes produced by animals, or around construction openings or wood piles. Indoor nests are in dark, undisturbed places such as under desks or furniture or in a basement. The spider frequently hangs upside down near the centre of its web and waits for insects to blunder in and get stuck. Then, before the insect can extricate itself, the spider rushes over to envenomate and wrap it in silk. To feed, the spider's mouth pulses digestive juices over the prey, which liquifies—and then the spider internalizes by capillary action, sucking the slurry into its mouth. Their prey consists of small insects such as flies, mosquitoes, grasshoppers, beetles, and caterpillars. If the spider perceives a threat, it quickly lets itself down to the ground on a safety line of silk.
As with other web-weavers, these spiders have very poor eyesight and depend on vibrations reaching them through their webs to find trapped prey or warn them of larger threats. When a widow spider is trapped, it is unlikely to bite, preferring to play dead or flick silk at the potential threat; bites occur when they cannot escape. Many injuries to humans are due to defensive bites delivered when a spider gets unintentionally squeezed or pinched. The blue mud dauber (Chalybion californicum) is a wasp that, in western North America, is the primary predator of black widow spiders.
The ultimate tensile strength and other physical properties of Latrodectus hesperus (western black widow) silk are similar to the properties of silk from orb-weaving spiders that had been tested in other studies. The tensile strength for the three kinds of silk measured in the Blackledge study was about 1,000 MPa. The ultimate strength reported in a previous study for Trichonephila edulis was 1,290 ± 160 MPa. The tensile strength of spider silk is comparable to that of steel wire of the same thickness. However, as the density of steel is about six times that of silk, silk is correspondingly stronger than steel wire of the same weight.
Spiders of the genus Steatoda (also of the Theridiidae) are often mistaken for widow spiders, and are known as "false widow spiders"; while their bite can be painful, they are significantly less harmful to humans.
Latrodectus