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Are there poisonous spiders in northern Idaho?

Two potentially poisonous spiders live in North Idaho, the Black Widow and the Hobo spider, also known as the aggressive house spider.


How do I recognize them with all the spiders out there?

The Black Widow is a shiny, inky black spider with a large round tail segment. The female measures one inch to one and a half inches in length. She has red to orange markings usually in the shape of an hourglass on her tail segment. Males are much smaller. Only females are known to bite people.

The Hobo spider is brown to light brown and one to two inches long from leg tip to leg tip. It's about the size of a quarter or silver dollar with no stripes or bands around its legs. It usually has a ^ marking on its back segment. Male spiders have the "boxing glove" appendages on the front while female spiders don't.


Where am I most likely to find them?

Black widows can be found in fields, wood piles, garages, attics, trash piles and other dark places. They're in all states except Alaska.

Hobo spiders are fast and tend to prefer low dark areas. They're not usually found on ceilings or walls. They build a funnel-shaped web that's open on both sides. They're uncommon above basements or ground level.


What will happen to me if they bite me?

A Black Widow doesn't always inject venom when it bites. Usually the bite is very painful, like a large pin prick, but some bites can go unnoticed. The venom is primarily a neurotoxin, which means it usually doesn't cause local tissue damage and destruction but instead affects the nervous system throughout the body. It can cause widespread muscle spasms, high blood pressure, nausea, sensitivity to light, difficulty breathing, diarrhea, body aches and headaches. It also causes acute abdominal pain which can mimic pain similar to an appendicitis attack.

In most cases, a small rash begins at the site of the bite about one hour after the bite. It slowly becomes larger with a ring appearance. Several rings may develop.


About half of Hobo spiders inject no venom and nothing happens to the person they bite. If they do inject venom, the person will experience an immediate redness around the bite site. The bite usually produces a slight prickling sensation. A small insensitive hard area appears around the bite site 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 open and the wound oozes. It then scabs over, but tissues beneath the scab continue to die. Surgical repair is sometimes needed.

The most common symptom is a severe headache. The fully developed lesion can vary from a half inch to several inches in diameter and may take several months to fully heal.


Is there treatment that will help?

Treatment for a Black Widow spider bite includes cleaning and washing the wound with soap and water as soon as possible. Apply an ice or cool compress. The limb where the bite occurred should rest. Some victims, particularly young children or people with high blood pressure, should be taken to the hospital and admitted overnight for observation and treatment.

Anyone who develops severe symptoms, including muscle aches, headaches, difficulty breathing, high blood pressure and stomach pain, should be taken to the hospital immediately for observation and treatment. There is anti-venom for Black Widow spider bites, but it is seldom necessary.

Treatment for Hobo spider bites includes thoroughly washing the bite site with soap and water. Keep the site immobilized and rested as much as possible. Antihistamines can be taken to control itching. The wound should be cleaned frequently and watched closely. A doctor should be consulted to monitor the progress of the wound. If the wound starts to show signs of darkening, a doctor should be consulted immediately. Wound healing can take several weeks to months to even years and leave a permanent scar. In severe cases, skin grafts may be required to fully heal the wound.



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