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Spiders of Medical Importance |
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| This page is from The Website for Young Marines |
Spiders as a whole are seldom aggressive, generally biting only when threatened or injured. Nearly all spiders have venom glands, but the toxicity of the venom to humans is so low as to be insignificant. The severity of the reaction to a spider bite is influenced by the species of spiders, the area of the body where the bite occurs, the amount of venom injected, and depth of the bite.
Widow Spiders
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 ( Figure 3). 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 it 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 4 days to 1 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 3 to 6 times before maturing. The females molt 6 to 8 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 Florida. 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 rainspouts. The northern black widow is found west of Tallahassee. It is mainly found in forests with irregular, loosely woven webs 3-20 feet above the ground. The red widow spider makes its web off the ground in palmettos 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 only in coastal cities located south of Daytona Beach where it 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 3 hours. In severe cases, later pain spreads to the abdomen, the blood pressure rises, there is nausea and profuse sweating, and difficulty in breathing occurs. 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.
Brown Recluse Spider
The brown recluse spider ( Figure 4) is not an established species in Florida, but physicians have diagnosed its bites. The brown recluse spider is recognized by having a dark violin-shaped mark located behind the eyes. There are 3 pair of eyes on this species while most spiders have 4 pair. The brown recluse is a medium-sized spider about 1/4 to 1/2 inch in length.
The brown recluse spider's natural habitat is along the Mississippi River valley, especially in northwestern Arkansas and southern Missouri. Because it can live in old boxes and furniture it is easily transported by humans. Specimens of brown recluse spiders have been found in Florida, but there reproduce in Florida's environment.
The brown recluse spider is a shy species that bites humans when trapped in clothing or rolled onto when people sleep in bed. Persons bitten by the brown recluse usually do not feel pain for 2-3 hours. A sensitive person may feel pain immediately. A blister arises around the area of the bite. The local pain becomes intense with the wound sloughing tissue often down to the bone. Healing takes place slowly and may take 6 to 8 weeks. If the bite of a brown recluse spider is suspected, collect the spider and consult a physician immediately.
Tarantulas
Tarantulas ( Figure 5) are not found naturally in Florida; however, some people keep tarantulas as pets. The term "tarantula" refers to about 300 species of spiders some of which can weigh 2 to 3 ounces and have a 10 inch leg span. Tarantulas are sluggish, will not bite unless provoked, and are not poisonous. However, the bites of tarantulas can be quite painful since the fangs are large and cause considerable mechanical damage to the victim.
Many tarantulas have a dense covering of stinging hairs on the abdomen to protect them from enemies. These hairs can cause skin irritation for humans. Most tarantulas that are desirable as pets have a bald spot on the abdomen and do not have stinging hairs.
Tarantulas usually live in burrows in the ground. These burrows may be dug by the spider or may be those abandoned by rodents. The tunnels are lined with silk and form a webbed rim at the entrance which conceals it. The females deposit 500 to 1000 eggs in a silken egg sac and guard it for 6 to 7 weeks. The young spiders remain in the burrow for some time after hatching and then disperse by crawling in all directions. Tarantulas do not occur in colonies since they do eat each other.
Tarantulas may live for many years. Most species require 10 years to mature to adults. Females kept in captivity have been known to live more than 25 years and have survived on water alone for 2 1/2 years. Females continue to molt after reaching maturity and therefore are able to regenerate lost legs. Males live for only one year or less after maturity.
A tarantula can be kept as a house pet. A terrarium (an empty aquarium) with a sandy bottom provides an ideal habitat. Tarantulas can be fed live crickets or other insects.
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