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 FLORIDA SPIDERS
A source for information on spiders

Black Widow Spiders    Laterodectus mactans

Appearance:
The adult female black widow has a shiny, jet-black spherical abdomen with an orange-red hourglass-shaped marking on its underside. The male’s abdomen has red spots and white lines or bars radiating out to its sides.

Size:
The body is about 1/4-1/2 inch long and 3/4 to 1 and ½ inches when legs are spread out.

Behavior:
The black widow spider’s venom is a potent neurotoxin and is considered the most venomous spider in North America. However, the female injects such a small dose of venom that it rarely causes death. They are timid and solitary, and often bite only when disturbed. All encounters with humans can be attributed to the female.

Black widow spiders tend to mate during spring or summer. The female lays 25-250 eggs in a ½-inch smooth, white silken sac, several of which may be produced during mating season. The egg sacs are suspended in the web and guarded by the female for about four weeks. They disperse by ballooning-exuding silk threads that are then transported by air currents. They mature in 2-4 months depending on availability of prey. Adults usually have a lifespan of one year.

The female constructs a very strong web of crisscrossed silk threads with a dense area of silk, usually to one side, which serves as the spider’s daytime retreat. At night, the female hangs belly upward with the hourglass marking visible, in the center of the web, and does not leave the web voluntarily. The web is usually situated near the ground in a dark, sheltered site. Webs often are one foot in diameter.

The black widow spider is widely feared because its bite results in severe pain that may take several days to subside. Such bites are rarely fatal but small children and elderly persons are at risk. Black widow spiders construct irregular, scaffold-type webs usually near the ground level. These webs are almost always constructed in a protected site such as among items piled together, beneath boards, in firewood, and between boxes. Newly hatched spiderlings climb to high points, release a strand of webbing and are propelled by "ballooning" to new locations. For this reason, buildings may have new spiderlings float to it on a regular basis. Most of these do not survive. Black widows eat any insect they can capture. It is not true that the female always consumes her mate after mating, but it does frequently occur. Black widows are classified as dangerous spiders because their bite can cause severe cramping and pain throughout the body. Very young children, the elderly, and very ill persons are most at risk for severe reactions to the bite of this spider.

Habitat:
Outdoors, black widow spider webs are usually built in wood and debris piles, under eaves, under stones, in hollow stumps, meter boxes, and other secluded areas. They are often found when homeowners carry firewood into the home. Black widows can also be found in outhouses, sheds, and garages. Indoors, they prefer secluded, cluttered areas in attics and crawl spaces. The web serves as a trap for the spider’s food supply, which includes a variety of insects, such as cockroaches and beetles, and other arthropods.

The black widow spider is essentially a southern species, but has been found as far north as Massachusetts. The northern black widow spider is similar to its southern counterpart except its habitat is marginal land with sparse vegetation. It is found in stumps, hollow logs, and debris piles, and only rarely indoors.

Bites most frequently occur when people are picking up an item under which the spider is hiding or putting on a shoe the spider has crawled into. Many bites are reported in outhouses where the black widow likes to spin her web below the toilet seat. (Be sure to check carefully before sitting down!) Black widows prefer to construct their webs in secluded, protected sites where insects are more likely to show up. Such sites are common in items stored haphazardly in garages or outside. Such clutter creates innumerable spaces suitable for spider harborage. Keeping boxes and objects stored neatly and away from walls is one step to minimize these spiders in or around a home.

Bite Signs and Symptoms:
The severity of a person’s reaction to the black widow spider bite depends on the area of the body bitten, amount of venom injected, and their sensitivity to the venom. The venom travels in the bloodstream throughout the body and acts on the nervous system, causing varying degrees of pain, which can sometimes be very intense.

Since there is no conspicuous swelling, the bite of a black widow spider may initially go unnoticed, but some people report a short stabbing pain. At first, there may be slight local swelling and two faint red marks, which are puncture points from the fangs. Pain soon begins and usually progresses from the bite site to the abdomen and back. Severe cramping or rigidity may occur in the abdominal muscles.

Other symptoms may include nausea, profuse perspiration, tremors, difficulty breathing, restlessness, increased blood pressure, and fever. Symptoms often diminish after a day or so and cease after several days. Serious long-term complications or death are very rare.

If bitten, remain calm, and immediately seek medical attention (contact your physician, hospital and/or poison control center). Apply an ice pack directly to the bite area to relieve swelling and pain. If possible, preserve the spider, regardless of its condition, for positive identification by a spider expert. A plastic bag or small jar or vial can be used to preserve it.

A hospital stay may be recommended, particularly for those with a heart condition or with health problems. A physician may administer a specific antivenin to counteract the venom or to relieve pain.
 

Control:
In order to prevent spider bites, be sure to wear gloves and a long-sleeved shirt when handling stored cardboard boxes, firewood, lumber, and rocks. Be sure to inspect these clothing items for spiders before putting them on. Shake out clothing and shoes before getting dressed.

Install tight-fitting screens on doors and windows to prevent entry of black widow spiders. Seal or caulk cracks and crevices where spiders can enter the house. Install yellow or sodium vapor light bulbs outdoors since these attract fewer insects for spiders to feed upon.

Discard old boxes, old clothing, lumber, and other unwanted items in attics, crawl spaces, garages, etc. In such areas, store any items off the floor and away from walls. Disperse piles of lumber and debris outdoors. Do not store firewood against the house.

  • Bites can be avoided by wearing heavy gloves when moving items stored for long periods outside, in garages, in basements or in warehouses.
  • Shoes should be stored inside shoeboxes or shaken vigorously prior to wearing.
  • When webs are visible, inspect carefully before putting your hand down under an object.
  • Control is best left to a professional company. If numerous spiders are encountered, they can be removed using a shop vacuum, but care must be taken when opening the vacuum to kill the spiders.
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