| Animal Fact Sheet
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Black Widow
Latrodectus mactans
What does it look
like?
The adult female black widow spider has a shiny, jet black, spherical
abdomen with two connected red triangles on the underside that form
a characteristic hourglass marking. Note, however, that the hourglass
color may range from yellowish to various shades of orange or red.
Adult females are about 1/2-inch long, not including the legs (about
1-1/2 inches when legs are spread). Adult males are harmless, about
half the female’s size, with smaller bodies and longer legs.
The male’s abdomen usually has red spots along the upper midline
and white lines or bars radiating out to the sides. Newly hatched
spiderlings are predominately white or yellowish-white, gradually
acquiring more black and varying amounts of red and white with each
molt. Juveniles of both sexes resemble the male and are harmless.
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| Where
in the world?
Black widow spiders inhabit warmer regions of the world to latitude
of about 45 degrees N. and S. They occur throughout all 4 deserts
of the American Southwest. Widow webs are commonly found in dark,
undisturbed places such as barns, garages, basements, outdoor toilets,
hollow stumps, rodent holes, trash, brush, and dense vegetation.
What are some behaviors?
The black widow's venom is a neurotoxin. The female is normally
shy and retiring, but aggressively attacks while guarding her egg
sac or if touched. Symptoms of a black widow bite include painful
rigidity of the abdominal wall muscles, tremors, nausea, vomiting,
leg cramps, and “tightness’” of chest, and rise
of blood pressure. Severe cases are hallmarked by difficulty in
breathing and unconsciousness, which may lead to death due to asphyxia
preceded by convulsions. Fewer than 5 percent of people bitten by
the black widow die.
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What
about offspring?
The black widow spider over winters as a young adult in buildings
or in sheltered places outdoors. In late spring, after a prolonged
courtship, mating occurs. Soon afterward the female begins laying
eggs. The males are frequently killed by the female after mating.
The grayish silken ball of eggs is attached to an irregular, tangled
web with a funnel-shaped exit. Each female constructs 5 to 15 egg
balls, each of which contains 200 to 900 eggs. Young spiders emerge
from the ball in 10 to 30 days. They are cannibalistic at this stage.
Only a few nymphs from each egg mass survive. They require 2 to
3 months to develop into adults. Older adults die the same summer
or autumn after laying eggs. The new generation of adults survives
through the winter.
What does it eat?
Black widows eat primarily insects and other arachnids that become
ensnared in the strong web. Occasionally small mammals or reptiles
that become ensnared in the web will be consumed as well.
Is it threatened
or endangered?
As a whole, all type of widow spiders are doing quite well and able
to sustain viable population. They are commonly killed on sight,
or controlled through the use of insecticides. |
