How do you identify widow spiders?
Mature female widow spiders generally are round in form and reach a length of about 1/4 to 1/3 inch. Adult spiders are distinctively shiny and dark colored, generally black or occasionally dark brown. The most commonly recognized feature of female black widows is the presence of a red or red-orange hourglass pattern on the underside of the abdomen. However, this pattern is variable and may occur as two unconnected spots. In a few widow spiders, no pattern is obvious on the abdomen.
The immature stages of both sexes and adult male widow spiders may have many red or red-orange or yellow spots and strips on the top of their abdomen. Immature females can be colored gray or pale brown, with numerous banding patterns. Darker coloration increases as they get older. The presence of an hourglass pattern on the underside of the abdomen occurs throughout their development.
Male widow spiders are much smaller (about 1/4 size) than the females. They usually are not black in overall color, instead appear light brown or gray and banded. Male widows may have an hourglass pattern, but coloration often is more orange and sometimes yellow. When mature, they have large knob-like structures (pedipalps) originating from the head. They are similar in appearance to immature females.
Widow spiders build loose and irregular mesh-type webs, often on plants, in loose stone or wood piles, or in the corners of rooms, garages or outbuildings. They do not produce the symmetrical web typical of orb weaving spiders (Araneidae) or the distinctive funnel pattern web of the funnel weaver spiders (Agelenidae).
What do the eggs of widow spiders look like?
Eggs of widow spiders are laid in an egg sack, attached to the web of the mother. The sack is pear shaped, and creamy yellow, light gray, or light brown in color. About 200 eggs may be laid in an egg sack and females may produce several egg sacks if conditions are favorable.
Where do you find black widows?
Widow spiders prefer to nest near the ground, in dark, undisturbed areas. Nest sites often are near holes produced by small animals, or around construction openings and wood piles. Low shrubs also are common sites for widows to occur.
Indoors, widows similarly occur in dark, undisturbed sites such as behind furniture or under desks. Undisturbed basement areas and crawl spaces of homes are also used by nesting widow spiders.
What are the symptoms of poisoning by widow spiders?
Widow spiders inject a toxin that affects the nervous system (neurotoxin). Muscle and chest pain or tightness are some of the most common reactions to the widow toxin. The pain also may spread to the abdomen, producing cramping and nausea. Other general symptoms include: restlessness, anxiety, breathing and speech difficulty, and sweating. Swelling may be noticed in extremities and eyelids but rarely at the bite site.
Often there is a general sense of discomfort shortly after the bite, and acute symptoms increase in severity during the firs day after a bite. Symptoms usually decline after two to three days but some mild symptoms may continue for several weeks after recovery.
How dangerous is the bite of widow spiders?
Only the bite of the female, usually the adult female, is potentially dangerous. Although extremely painful and temporarily debilitating, fatalities from untreated widow bites are uncommon. During the period between 1926 to 1943, mortality ranged from 4 percent to 5 percent, but current medical treatments have reduced this to a much smaller incidence. Death usually results from respiratory paralysis. The very old, very young, and those with a history of high blood pressure (hypertensive) are at greatest risk.
Prompt medical treatment can greatly reduce the danger from widow bites and has reduced fatalities to extremely low rates in recent years.
Can black widow bites by treated?
Because of the possible severity of black widow bites, immediate medical attention is important. Physicians can intravenously inject calcium gluconate to counteract most effects of the toxin. The injection helps bolster levels of calcium salts that are depressed by the effects of the bite. A black widow antiserum also is available, although effects usually are less dramatic than the calcium gluconate treatment.
First aid prior to the physician visit involves treating the bite site with antiseptics to prevent infections and trying to keep the patient quiet and warm. Because the toxin moves quickly in the body, attempting to suck out the poison is ineffective.
When do bites occur?
Widow spiders are not aggressive and bites can be infrequent even when large numbers occur. The adult female spiders usually remain in their webs unless forced by adverse temperatures or destruction of their web. They do not forage for food and the insects they eat are caught in the webs and eaten at the site. Human bites mostly occur as the spider defends her web if it is brushed against or accidentally pinched.
Occasionally, bites occur from hungry widow spiders when a hand or foot is dangled in front of the nest. Before indoor plumbing, bites were fairly frequent in outhouses, particularly on male genitals.
Does the bite hurt?
Black widows, and other spiders, bite using a pair of fangs known as chelicerae. The bite can go unnoticed, although it often produces an immediate sharp, pin-prick pain. A slight swelling and redness may develop at the bite site.
What precautions can be taken to avoid bites?
Encourage everyone in the family to learn about black widows so they can readily identify and avoid them. It is also a good idea to wear gloves and a long-sleeved shirt when working in spider infested areas.
How can one control black widows?
Periodically check areas in and around the home where black widows may occur. When discovered they can be most effectively destroyed by crushing or vacuuming the wed and spider, using protective methods. Spiders also can be discouraged by increased lighting of darkened corners, such as by appropriate furniture arrangement or use of artificial lighting.
Insecticides can be useful for spider control but do not control all spiders. If you choose to apply an insecticide, do so to the dark, undisturbed areas where spiders are likely to produce webs. Insecticides also can be used to prevent spider migrations into homes by spraying around the exterior foundation and lower story windows. Do this before cold weather forces spiders (and many insects) into homes to seek shelter.
Presently, the insecticide chlorpyrifos (Dursban) is the most widely available product for control of spiders around a home. Chlorpyrifos has a residual effectiveness of several weeks, particularly if not exposed to light and moisture. It is moderately toxic to humans. Carefully read and follow all use directions with any pesticide.