Montana State University |
Montana State University |
BOZEMAN (August, 1994) - -Two aggressive house spiders have been identified in Montana in areas not usually considered their habitat, says a representative of the Montana State University Insect Diagnostic Lab. (See also "Symptoms, Diagnosis and Treatment of Aggressive House Spider Bite compared to Brown Recluse" and "Spider Identification and Management.")
"We've said its main habitat is west of Great Falls," says Will Lanier of the Lab, "but both of the examples so far this year come from east of there." Specimens have been identified from Valley and Sweet Grass counties, says Lanier.
"This is the time of year the aggressive house spider begins to roam, because they're looking for mates," says Lanier. Because of that, it is also the time when people are most likely to be bitten.
Aggressive house spider venom produces skin ulcers which are often mistaken for the brown recluse spider bites. People who get bites that get bigger and ulcerate rather than going away in the Northwestern United States should suspect the aggressive house spider rather than the brown recluse.
The distinction between the types of spiders is important, because it can help you prevent bites by the aggressive house spider and help you know how to rid your home of them, says Lanier.
The aggressive house spider rarely climbs upward. That means you usually find them on ground or lower floors. It likes tall or matted grass, cracks and crevices. Repair and maintenance of door and window casings to reduce holes and cracks big enough to admit spiders is effective. Other possible entry points are around water pipes and electrical lines, these should be well caulked.
The aggressive house spider got its name because it will stand its ground when cornered and bite when provoked. It became common in the Pacific Northwest in the 1960s and many instances of it were found in Montana last year. It has been thought to be most common west of Cascade county.
The preference of this spider for small dark places suggests the design of a good trap, says Lanier. A cardboard tube with an adhesive, like "Tangle foot adhesive" about an inch inside the mouth with and one end covered can catch and hold the spider. A commercial version of this trap is the "Enforcer Mouse Glue trap."
You should scout the perimeter of lower level rooms and trap locations once a day. Dispose of the spiders with a broom or shoe heel. If you use a vacuum, you need to dispose of the bag.
Commonly, spider bites occur when a homeowner picks up firewood with a spider on it or when the spider is on clothing and is trapped as the clothing is put on.
"The initial bite isn't supposed to be painful," says Lanier. However, a small, insensitive hard area appears within 30 minutes and a red area expands to two-to-six inches in diameter. Blisters form and about 24 hours after later they break. The wound scabs and tissue beneath the scab may die. It may take several months for the wound to heal, and it may leave a scar. In some cases surgery was needed.
The most common symptom is a severe headache that does not respond to aspirin. The headache may persist for two to seven days, and is sometimes accompanied by nausea, weakness, tiredness, temporary loss of memory, and vision impairment.
Though bites by the aggressive house spider have not caused a death, a person bitten by one should seek immediate medical treatment.
Suspicious spiders should be taken to the local MSU Extension office or mailed in a leak-proof vial of alcohol directly to Lanier at the Entomology Diagnostic Lab, Montana State University, Bozeman, MT 59717.
Send questions or comments to Carol Flaherty, MSU Communications Services, Bozeman, MT 59717 or email her at carolf@montana.edu
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