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Introduction
Spiders are predators that feed on insects and other arthropods. Most often they are quite beneficial to our environment, and are harmless. In the United States 20,000 different species have been identified and only four occasionally are harmful to humans. In Arizona, brown and widow spiders have been associated with significant pathology and very rare reports of death.
In the case of a spider bite, contact a physician or your state Poison and Drug Information Center as soon as possible for advice and assistance. If possible, collect the spider to aid diagnosis and correct treatment procedures.
The Brown Spider
The brown spiders (Loxosceles spp.)are often mistakenly referred to as brown recluse spiders. Adult brown spiders are brown in color and the body is about a half an inch long. Their legs are long and delicately covered with short, dark hairs. The leg span is about 1 1/2 – 2 inches as adults.
Distinguishing characteristics include the three pairs of eyes arranged in a semicircle on the top of the cephalothorax (combined head and abdomen) and a violin-shaped marking immediately behind the eyes. This marking also gives them the name “fiddleback” or “violin spider.”
Most brown spiders are found living in large numbers. Males, females and even spiderlings are capable of venomous bites creating a disease state now known as necrotic arachnidism.
The bite itself is often unnoticed and the severity of the reaction varies greatly between individuals. In the case of necrotic arachnidism, the bitten area becomes painful, swollen and blistered within hours. This site will evolve into what has classically been described as a bulls-eye lesion with a dark center (dead skin) outlined by white and set on a red and inflamed background. It is several weeks before the blackened area falls away, leaving a pit of scar tissue. On rare occasions, the response involves a large amount of tissue destruction and a serious life-threatening systemic reaction. The most up-to-date treatment includes the use of a hyperbaric chamber, which eliminates ulceration of bites and applying Dapsone® to the wound site.
Black widow
The common “black widow” spider specifically refers to the eastern species Latrodectus mactans, which does not occur in Arizona. Our widow species Latrodectus hesperus is however very similar in appearance to the true black widow. Only the female is venomous. They are shiny black and about 1.5 inches long. The famous characteristic mark is the reddish hourglass shape on the underside of her abdomen.
Like the brown spider, the bite itself is not terribly painful, but local pain does follow very shortly after. The venom can cause abdominal pain similar to appendicitis as well as pain to muscles and the soles of the feet. Other symptoms include alternating salivation and dry-mouth, paralysis of the diaphragm, profuse sweating and swollen eyelids. Most healthy people recover rapidly in two to five days but the rare fatalities that occur are due to heart and lung failure.
If bitten, clean the site well with soap and water. Apply a cool compress over the bite location and keep the affected limb elevated to about heart level. Aspirin or acetaminophen may be taken to relieve minor symptoms.
Tarantula
Tarantula spiders belong to the family Theraphosidae. They are our largest spiders. The males can reach a length of 2 to 2 ½ inches and the female 4 inches. These spiders feed on arthropods and small vertebrates such as mice, lizards and snakes. They can live as long as 20 years. All species are nocturnal, living in holes that they construct. During our late summer months the males are seen moving through the desert in search of mates. Tarantulas are usually very timid and secretive. When threatened they can bite. They have large fang-like chelicerae that can cause some pain. Their venom is usually harmless to humans. Another method of defense is using the hind legs to rub hairs off the top of the abdomen. This cloud of fine hairs can be irritating to the eyes and mucus membranes so be careful when handling these spiders.
Prevention
- Perform routine, thorough house cleaning, particularly storage areas (closets, basements, attics, etc) and behind outside shutters. Regular dusting and clutter reduction removes hiding places. Pay particular attention to doors, windows, vents and along foundations.
- Reduce clutter in garages, attics, and basements.
- Reduce clutter in storage cupboards; do not place your hands where you can not see what you are picking up.
- Trim weeds around the building foundation and remove firewood, building materials, and debris to discourage insects and spiders from living next to a structure. Reduction of heavy dense vegetation will help reduce spider populations.
- Install tight-fitting window screens and door screens.
- Consider installing yellow or sodium vapor light bulbs outside entrances because these lights are less attractive to insects and thus draw fewer spiders to the area.
- Follow the guidelines for general exclusion e.g. sealing cracks, fitting door sweeps and eliminating other possible entry points to prevent spiders from moving indoors.
- Use a vacuum to remove webs, unwanted spiders and egg sacs on a continuous basis.
- Learn to recognize brown and widow spiders and instruct other members of the household.
- Do not collect wood from woodpiles out-ofdoors without wearing gloves. Place wood from outside directly on fires. Do not store indoors.
- Chemical control need only be considered if there are a number of bites reported in the area and occupants are at risk. The widow spider is resistant to many insecticides so check the label. However, brown spiders and widow spiders can simply be vacuumed. A small amount of boric acid crystals can be vacuumed up prior to cleaning out spiders and webbing. To be extra careful, remove the vacuumed bag and discard in an outside garbage container immediately after vacuuming.
