Pest Library
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All it takes is one pest sighting to ruin the reputation you’ve worked so hard to build.
Black Widow Spider
Lactrodectus spp
The black widow spider is a poisonous spider, with venom 15 times more poisonous than that of a rattlesnake. Their venom contains a toxin that affects the nervous system and can cause paralysis, but because they are so small, their bite is rarely fatal to humans.
RISK LEVEL:
LOW
MEDIUM
HIGH
Risk is defined as how much damage each pest can be to you, your family, or your home
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| Class: | Order: | Family: | |
| Arachnida | Araneae | Theridiidae | |
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| 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. |
| 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. |
| 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. |
| 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. |
| 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. |
- If you see a spider with a red color spot or pattern, it is most likely a black widow.
- Their body is almost round in shape.
- Often congregate in old storage areas or places often undisturbed.
- They usually do not live through summers.