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Brown Recluse Spider Bites

- May cause a serious, localized wounds -

Summary: The brown recluse spider occurs in the south central US and is commonly found indoors. While authenticated bites are relatively rare the spider's hemolytic (haemolytic) venom can result in wounds that are slow to heal and secondary infections are also common.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Brown recluse spider (Loxosceles reclusa)

Unfortunately there is a lot of misinformation about brown recluse spiders. In this article I'll try to sort fact from fiction and give you some solid guidelines for dealing with this spider.

Brown recluse spiders are medium size (20-40 mm leg span [a US quarter is about 25 mm]; body length ~10 mm), tan to brown in color and have a very distinctive "violin" shape mark on the spider's upper surface, or cephalothorax (photo of a brown recluse showing "violin" mark). The brown recluse spider is a hunting, wandering spider and does not use a web to capture prey.

Brown recluse spider map

The distribution of brown recluse spider is much more limited than many people believe. It occurs only in the south-central US [see this range map of where this spider lives]. A related species occurs as far west as California but apparently does not bite causing wounds. Reports of bites from outside the map area probably are misdiagnosed.

common names: violin spider, fiddleback spider

brown recluse spider drawing

Brown recluse spider - drawing. Body length less than 1/2". Note violin-shaped mark on back (arrow). The "violin" has a thin neck and wide body. The neck of the violin is pointing backwards.


Reports of brown recluse outside this range?

The brown recluse spider is often reported from outside its natural range based only are on wounds (no specimen to identify) and many slow-healing necrotic wounds have been mistakenly blamed on this spider. Within its home range, however, the brown recluse spider can be very common and abundant but authenticated bites are relatively rare.

Like other wandering/hunting spiders brown recluse spiders are sometimes found associated with packing materials and shipped goods. For this reason lone spiders will occasionally be found elsewhere. It is highly unlikely that these displaced spiders will survive and colonize the new area.


Brown recluse spider venom

Brown recluse spiders have very small fangs and cannot bite through clothing so most bites occur when the spider is accidentally pressed against bare skin. Initially the bite is painless but sometime later (1-8 hours) the area becomes tender, red and swollen, and many bites heal without further complications. Some bites, however, progress to serious necrotic wounds that can develop into dangerous medical conditions especially in individuals with a compromised immune system. Wounds tend to be localized skin lesions that are slow to heal and eventually leave a deep scar. Many conditions mimic brown recluse spider bites and some, such as diabetes, can exaccerbate the injury.

Spray for brown recluse spiders?

Not indoors. Spiders are very difficult to treat with conventional insecticides especially for homeowners because they move so readily from area to area. Plus, I believe it is unwise to apply conventional insecticides indoors where you are continuously exposed to these materials. A better approach is to use spider traps (see Making and Using Spider Traps). Purchase or make traps and continue trapping until you no longer catch spiders on a daily bases. On rare occasions it may make sense to treat an area of known heavy infestation if it is located away from the living area such as an attic or crawlspace.

However, insecticide applied to the exterior foundation below the siding ("perimeter spray") may prevent spiders from migrating into the livings areas. Onslaught Microencapsulated Insecticide (available here) is approved for this treatment (see a current label for approved uses).

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Jack DeAngelis, PhD,  , email:  [email protected]

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