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When Poisonous Spiders Bite

Spiders are arachnids. This is the same group of animals that includes ticks, mites, and scorpions. All arachnids have 8 legs. Insects have only 6 legs.

No matter where you live, you'll find spiders in and around your home. Although all spiders have mouth parts that can bite, most spiders aren't dangerous to people. Depending on the type of spider, it's either because its venom isn't toxic to people, or its mouth parts aren't strong enough to bite through human skin.

There are 2 types of spiders found in the United States that can cause illness in people. One type is the widow spider. The black widow is the best known. The other type is the recluse spider. The brown recluse is the best known. A bite by either type usually is not deadly, but it may make a person very sick. It's important to get quick medical help if you think you've been bitten by either type of spider.

Symptoms

You may not notice a bite by either a black widow or a brown recluse spider may at first. The bite is usually described as feeling like a pinprick or a light sting.

Children and spider bites

Children are more sensitive than adults to spider bites because of their smaller body size. But deaths from bites either of the black widow or the brown recluse are very rare. It is important to protect children from spider bites as the symptoms described below can be more severe in children

Treatment

If you are bitten by either a black widow or brown recluse, see your healthcare provider right away or go to the emergency room. Antivenin is available for black widow bites, but none is available for brown recluse bites. The antivenin is only used in the most severe cases. Other treatment is mostly to ease symptoms. The site of the bite should be cleansed and cold packs applied. Tetanus shots should be given.

Preventing bites

Both the black widow and brown recluse spiders are shy and avoid areas of a home with lots of activity or open spaces. They prefer quiet corners of a home, dark areas under seldom-moved furniture, garages, sheds, and wood piles. Neither spider is overly aggressive. They usually bite only when provoked or trapped against the skin.

Teach your children to not reach into areas where spiders may live without first checking to make sure no spiders are there. Webs and dead insects in an area usually show that spiders are active there. Children also should not play around rock piles and woodpiles.

If you do yard work that includes handling logs or leaves, wear gloves. Shake out any blankets or clothes that have been stored in an attic or basement before using them. Carefully check shoes or boots stored in a mudroom or garage before putting them on.

You can limit the number of spiders in your home by having it sprayed with insecticide. Be sure to use only a licensed pest control company to do this. Insecticides carry their own risks, particularly if children, pets, or pregnant or nursing women are in the home.

Recognizing poisonous spiders

Widow spider (Black widow)
Black widow

Widow spiders. There are 5 different species of widow spiders, including the "black widow," in the United States. Of these, only 3 are black, and only the black widow has the classic reddish-orange "hourglass" shape on its belly. The bite of any of the widow types can cause a fairly severe reaction. The black widow causes the most frequent and severe poisonings. Black widows are not aggressive spiders unless they are provoked. They generally live in dark, quiet, undisturbed areas in and around a home like closets and basements.

Brown Recluse
Brown recluse

Recluse spiders. There are 12 species of recluse spiders, including the brown recluse, in the United States. Only half of these are responsible for bites that have a major reaction in people. Most of the spiders in this group have a violin/fiddle-shaped markings on the upper part of their body with the base at the front of the head and the neck of the violin pointing towards the rear of the spider. Besides the brown recluse, the other poisonous spiders in this group can be gray, orange, reddish-brown or pale brown. Like the black widow, the recluse spiders like quiet, dark, undisturbed areas in and around the home. They are nighttime spiders, so they come out mostly at night or when the light is dim.

If you are bitten by a black widow spider, the area of the bite may begin to swell and hurt after about a half hour. The venom of a black widow spider is a neurotoxin. This means it affects the nerves and the brain. These are symptoms of a black widow spider bite:

Black Widow spider bite

  • Muscle cramps or twitches, usually near the site of the bite

  • Muscle spasms all over the body, sometimes within an hour of the bite

  • Severe belly pain, sometimes accompanied by nausea and vomiting

  • Increased blood pressure

  • Sweating

In severe cases, a person may become unconscious or stop breathing. Death from a black widow bite is extremely rare. If it does happen, it is more likely in children younger than 2 or in adults older than 50.

If you are bitten by a brown recluse spider, pain and itching at the site of the bite will begin to increase after 4 to 8 hours. The venom of a brown recluse spider is a tissue poison. This means it can severely damage the skin around the bite. These are symptoms of a brown recluse spider bite, in the order they appear:

Brown Recluse spider bite

  • Redness and swelling happen first at the site of the bite.

  • A blood-filled blister forms at the site soon after that.

  • An ulcer follows several days later, after the blister breaks and the skin falls away. The ulcer slowly gets bigger and creates a layer of dead issue. Some ulcers may reach 7 inches in diameter. Some of these ulcers need to be surgically repaired with skin grafts.

  • In rare cases, a person may have a life-threatening breakdown of red blood cells.

Other symptoms may include fever and chills, nausea and vomiting, joint pains and rashes.

Online Medical Reviewer: Daphne Pierce-Smith RN MSN CCRC
Online Medical Reviewer: Donna Freeborn PhD CNM FNP
Online Medical Reviewer: Eric Perez MD
Date Last Reviewed: 2/1/2019
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