Size: |
Black widow spider adult female is about 1/2 in (12-13
mm) long, including the abdomen which is 1/4-3/8 in (7.2-9.6 mm) in
diameter; length including legs is 1 1/2 to 1 3/8 in (38-43 mm); male
is half that size. |
Characteristics: |
The abdomen is almost spherical. The common name comes from the
belief that the female eats the male after mating, which rarely happens
in nature. |
Color: |
Females are usually black, sometimes brownish, with 2 reddish triangular
markings on her underside that are often joined so they look like
an hourglass shape, but are sometimes only a single triangular mark.
There are usually red markings above the spinnerets. Males usually
have a color pattern on upper surface, a row of red spots with white
lines or bars going out to the sides. Eyes: 8, with 2 side pairs almost
touching. Last tarsal segment of 4th pair of legs has toothed bristles;
claws on all lower leg segments. Young spiders are orange and white,
becoming more and more black with age, with markings like males on
upper side; also 1 or 2 reddish markings on underneath side. |
Geographic Range: |
Around the world; 5 species in the United States. Lactrodectus
hesperus, the western widow spider, is found in the western U.S. and
western Canada. |
Comparison with other species: |
Widow spiders are all quite similar to each other, but are distinct
from other spiders. (See Characteristics above.) |
Habitat: |
Black widow spiders live in protected places such as woodpiles,
under stones and decks, in hollow trees or stumps, rodent burrows,
or even in low branches; dry places in barns, sheds, meter boxes,
barrels. |
Food: |
Insects. Black widow spiders hang upside down from irregular webs
one foot in diameter. The female avoids light and tends to seek prey
at night. |
Biology: |
Most black widow spiders overwinter as immatures, becoming adults
in spring, dying in late July. In some species females may live for
2 or more years after maturity; and some males up to about 6 months.
Development from egg to adult takes nearly a year. Incubation period:
8-30 days. Females lay eggs in closely woven silk sacs 3/8-1/2 inches
in diameter that turn from white to pale brown. Spiderlings have first
molt within egg sac. 2nd instar spiderlings spin silk threads and
"balloon" out on a breeze. There are 4-9 instars in 54-107
days, each instar with a different color and/or pattern. |
Invasion: |
They may enter seldom-used, cluttered parts of garages, basements,
crawl spaces. |
Damage: |
Only the female's bite is poisonous. The male does not develop
venom sacs into maturity, and does not attack prey as an adult. Spiderlings
are poisonous only if eaten during first 18 days, but lose their poison.
Adult venom is different, a neurotoxin. Female is not aggressive except
after egg laying and when guarding her eggs. |
