Poisonous Spiders

Introduction

The spiders listed on this page commonly are found within nurseries. While they can be listed as predators of insects, the insects they prey upon are more likely to be beneficial insects rather than insect pests. Their source of food aside, they are included here because they are also poisonous and may cause problems with nursery employees.

Most spider bites are not likely to be dangerous, but medical care and advice should be sought in each case and it is important to save any biting spider so it can be identified.

Widow Spiders

The black widow spider is found throughout the western hemisphere, and is extremely common in the southern United States. In fact, four species of widow spiders occur in Florida: the southern black widow, the northern black widow, the red widow and the brown widow. All these species are rather large spiders, about 1 1/2 inches long with the legs extended.

The southern black widow and the northern black widow are a shiny, jet-black color. The southern black widow has a red hourglass marking on the underside of the abdomen and another red spot at the tip end of the abdomen. The northern black widow has a row of red spots located in the middle of its back and two reddish triangles resembling an hourglass on the underside of the abdomen. The red widow spider has a reddish orange head-thorax and legs with a black abdomen. The abdomen may have a dorsal row of red spots with a yellow border. The red widow lacks a complete hourglass under the abdomen, but may have one or two red spots. The brown widow spider varies in color from gray to light brown or black. The abdomen has variable markings of black, white, red, and yellow. On the underside of the abdomen the brown widow has an orange or yellowish-red hourglass marking.

The life cycle of the widow spiders are all similar. The female lays approximately 250 eggs in an egg sac which is about 1/2 to 5/8 inch in diameter. The eggs hatch in 20 days and remain in the egg sac from about four days to one month. The young spiders then molt to the second stage and begin feeding. As the young spiders grow, they construct a loosely woven web and capture progressively larger prey. Male spiders molt three to six times before maturing. The females molt six to eight times and occasionally eat the males after mating. In Florida all the widows, except the northern black widow, breed year-round.

The southern black widow is the most widespread widow spider in the southern states and is also found as far north as Massachusetts. It is usually found outdoors in protected places such as in hollows of stumps, discarded building materials, rodent burrows, storm sewers, and under park benches and tables. Around houses, the southern black widow is found in garages, storage sheds, crawl spaces under buildings, furniture, ventilators, and rain spouts. The northern black widow is found west of Tallahassee and in states north of Florida all the way to, and including, Canada. It is mainly found in forests in irregular, loosely woven webs three to 20 feet above the ground. The red widow spider makes its web off the ground in palmetto habitats and has only been found in sand-pine scrub associations. The web retreat is characterized by the rolled palmetto frond, and the web is spread over the fronds. The brown widow is found most often south of Daytona Beach, Florida along the coast and was once confined there, but it has extended it range and is now found throughout peninsular Florida and has been recorded as far north as South Carolina. It is also known from Texas and Louisiana and probably occurs all across the Gulf states and the panhandle of Florida. The brown widow usually lives on buildings in well-lighted areas.

Like most spiders, the widow spiders are shy and will not bite unless aggravated. All four species have a strong venom. The southern black widow is involved in most poisonous spider-bite cases in Florida. The bite of the black widow is not always felt, but usually feels like a pin prick. The initial pain disappears rapidly leaving a local swelling where two tiny red spots appear. Muscular cramps in the shoulder, thigh, and back usually begin within 15 minutes to three hours. In severe cases, later pain spreads to the abdomen, the blood pressure rises, there is nausea and profuse sweating, and difficulty breathing. Death may result from the venom, depending on the victim's physical condition, age, and location of the bite. However, death seldom occurs if a physician is consulted and treatment is prompt.

If you suspect that a widow spider has bitten you, capture the specimen for identification and immediately consult a physician. For additional information, your doctor may wish to contact your local poison control center.

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