Special to the Montana Medical Association and CA.
BOZEMAN -- Again this year, the bite of the aggressive house spider in Montana is being confused with that of the brown recluse spider, according to Montana State University-Bozeman Extension agents asked to identify spiders. Distinguishing between the two is important for treatment and to prevent future bites. "Brown recluse spiders are not native to Montana or any state adjacent to Montana, though they could be present in lumber shipped in from milder climates," says Will Lanier, MSU-Bozeman Extension insect diagnostician. "However, the aggressive ho use spider is native to the area and causes an ulcerating bite similar to the recluse."The aggressive house spider tends to climb downward. It is usually found on ground or basement levels, often entering through windows. Vacuuming lower levels can eliminate nests, but if this is done the bag should be disposed of so spiders cannot escape. Worn or damaged window and door seals, where spiders can enter, should be repaired. In addition, firewood should be inspected for spiders and egg-sacks before being brought into the home, and wood piles should be kept away from the house. Chemical control of spiders is possible, but both cost and risks of pesticides in the home make chemical control less suitable than other measures. Though the literature suggests that spider bites are of minimal medical importance, the bite of the aggressive house spider may require prolonged treatment and leave a scar, says Robert Flaherty, a Bozeman physician.
Symptoms:The aggressive house spider's bite initially produces a slight prickling sensation. A small insensitive hard area appears within 30 minutes, surrounded by an expanding reddened area of two to six inches in diameter. Between 15 and 35 hours after the bite, the area blisters. About 24 hours later, the blisters break and the wound oozes. It scabs over, but tissues beneath the scab continue to die. Surgical repair is sometimes needed. The most common symptom in addition to the bite is a migraine headache.The fully developed lesion can vary from one-half to one-inch or more in diameter and may take several months to heal.
Treatment: Aggressive house spider bites generally require only local wound cleaning, topical antibiotics and tetanus prophylaxis. Skin grafting is rarely necessary. In contrast, treatment of brown recluse bites involves cleaning the wound, applying topical antibiotics and tetanus prophylaxis. Topical corticosteroids are not helpful, but systemic corticosteroids and dapsone may be helpful. Skin grafting is sometimes necessary.
Diagnosis is difficult because the spider is rarely seen or recovered. If a spider is not captured in the act or vicinity, all evidence is circumstantial. The resulting effects of the bite should be carefully compared to those associated with systemic arachnidism. If unsure, a doctor should state "possible arthropod envenomation, vector unknown" in the medical record. Of 60 spiders that can cause medical complications in humans, only two exist in Montana: the aggressive house spider (Tegenaria agrestis) and the black widow spider (Latrodectism), says Lanier. The aggressive house spider is a common biter. It is easily provoked and will be aggressive when crowded. This may be due to the fact that its web is not sticky, so it must attack the entangled prey or lose it.
The black widow spider's venom is the more serious. It is a neurotoxin, so it affects muscle coordination and nerve endings.However, the black widow spider is not aggressive. Black widow bites often occur when a spider is trapped in clothing and being crushed.
Help in spider identification and control is available at your local Extension office where you also could pick up the free MontGuide 9210 "Spider Identification and Management." Handling costs $2.95 if the MontGuide is ordered from MSU Extension Publications, 115 Culbertson Hall, Bozeman, Mont. 59717. Medical professionals can review spider related information on the Virtual Medical Center, a computer bulletin board at (406) 994-2564. (Carol Flaherty Montana State University)
A survey of recent literature concerning spider bites shows that they are of minimal medical importance. This is especially true in Montana. Of the 60 spiders that can cause medical complications in humans only two exist in Montana, the Tegenaria agrestis or Aggressive House spider (Hobo spider) and the Latrodectism or Black Widow spider. Contrary to popular belief and the knee jerk reaction of many professionals the Brown Recluse spider does not exist in Montana or a state bordering Montana. Your Doctor should know!
The fear of Brown recluse spiders does exist in Montana because spider bite diagnosis is very difficult and the Brown Recluse is a popular culprit. This fear exists because rarely is the spider blamed for the bite seen or recovered. It is essential for medical and medicolegal reasons that professionals be absolutely sure of their diagnosis.
The basic facts about the physical ability of spiders to bite humans places them near the bottom of the list. The ability of most spiders to bite a human could be compared to our ability to bite a plaster board wall in a house. The angles of a spiders mouth are all wrong. If a spider is not captured in the act or vicinity all evidence is circumstantial. The resulting effects of the bite should be carefully compared to those associated with systemic arachnidism. If none of the above has occurred a doctor should state “possible arthropod envenomation, vector unknown” in the medical record.
Of the spiders that do occur in the Pacific Northwest the Aggressive House spider is a common biter. Aptly named since this spider is easily provoked and unlike the Black Widow (which will die trying to escape a human) the aggressive house spider will act in an aggressive manner when crowded. This characteristic is sometimes attributed to the non-sticky nature of the aggressive house spiders web. Prey captured in the web are more able to extract themselves, thus the aggressive house spider must attack the entangled prey in a timely manner or lose it.
The Black widow spider’s venom is the most serious of the two. The venom of the Black Widow is a neurotoxin, so it affects muscle coordinate and nerve endings. The good side of the Black Widow is that they are not aggressive. For example, Black Widow bites and others occur as a last act of revenge, when the spider is trapped in a piece of clothing and being crushed by its use.
Control of spiders is best accomplished by reducing suitable environments. Spiders look for nooks and crannies to hide in, irregular surfaces allow them to attach webs and offer daytime hiding places to those spiders which prefer night time activities. Poorly maintained window and door seals allow the spiders wandering around a building’s foundation to gain access. Chemical control of spiders is possible but the cost and risks of introducing pesticides into the living environment make chemical control a less effective control measure.
Assistance in identification and control of spiders is available from your local Extension office. Medical professionals can review spider related information through the Virtual Medical Center, a computer bulletin board at (406) 994-2564.
Categories: Spider Bites, Brown Recluse, Hobo Spider, Black Widow