Black Widow Spiders

 

 
IDENTIFICATION Spiders resemble insects and sometimes are confused with them, but they are arachnids, not insects. Spiders have eight legs and two body parts–a head region (cephalothorax) and an abdomen. They lack wings and antennae. Although spiders often are found on plants, they eat mainly insects, other spiders, and related arthropods, not plants. Most spiders have toxic venom, which they use to kill their prey. However, only those spiders whose venom typically causes a serious reaction in humans are called "poisonous" spiders.

Black Widow Spider

The black widow spider, Latrodectus hesperus, is the most common harmful spider in California. Venom from its bite can cause reactions ranging from mild to painful and serious, but death is very unlikely and many symptoms can be alleviated if medical treatment is obtained. Anyone bitten by this spider should remain calm and promptly seek medical advice; it is helpful if the offending spider can be caught and saved for identification.

The typical adult female black widow has a shiny black body, slender black legs, and a red or orange mark in the shape of an hourglass on the underside of the large, round abdomen. The body, excluding legs, is 5/16 to 5/8 inch long. The adult male black widow is one-half to two-thirds the length of the female, has a small abdomen, and is seldom noticed. The male black widow does possess venom, but its fangs are too small to break human skin. The top side of its abdomen is olive greenish gray with a pattern of cream-colored areas and one light-colored band going lengthwise down the middle. The hourglass mark on the underside of the abdomen typically is yellow or yellow-orange and broad-waisted. The legs are banded with alternating light and dark areas. Contrary to popular belief, the female black widow rarely eats the male after mating, but may do so if hungry. Like males, young female black widow spiders are patterned on the top side. In the early stages they greatly resemble males, but gradually acquire the typical female coloration with each shedding of the skin. In intermediate stages they have tan or cream-colored, olive gray, and orange markings on the top side of the abdomen, a yellowish orange hourglass mark on the underside, and banded legs. Only the larger immature female and adult female spiders are able to bite through a person’s skin and inject enough venom to cause a painful reaction.

Webs and Egg Sacs. The web of the black widow is an irregular, tough-stranded, sticky cobweb mesh in which the spider hangs with its underside up. During the day it often hides under an object at the edge of the web or stays in a silken retreat in the center. The black widow may rush out of its hiding place when the web is disturbed, especially if egg sacs are present. The egg sacs are mostly spherical, about 1/2 inch long and 5/8 inch in diameter, creamy yellow to light tan in color, opaque, and tough and paperlike on the surface. A female may produce several egg sacs. Tiny, young black widows, which are nearly white in color, disperse to new locations by ballooning and infest new areas.

Effects of the Bite. The symptoms of a black widow bite are largely internal; little more than local redness and swelling may develop at the bite site. The internal effects may range from mild to severe. Pain tends to spread from the bite to other parts of the body and muscular spasms may develop. In severe cases the abdominal muscles may become quite rigid. Other effects can include profuse sweating, fever, increased blood pressure, difficulty breathing and speaking, restlessness, and nausea. Typically, the pain and other symptoms reach a maximum within a day of the bite, then gradually subside over the next 2 to 3 days. Most people who are bitten spend a few hours under observation by a physician but do not develop symptoms severe enough to require treatment. Small children, the elderly, and persons with health problems are likely to suffer some of the more severe consequences of the bite. Black widow bites are fairly common in California.