Wilderness Medicine, First Aid, and Outdoor Skills
Spider Bites

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Spider Bites
 - Brown Recluse Bites
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US Army First Aid Manual
Fundamental Criteria for First Aid
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Appendix A: First Aid Case and Kits, Dressings, and Bandages
Appendix B: Rescue and Transportation Procedures
Appendix C: Common Problems/Conditions
Appendix D: Digital Pressure
Appendix E: Decontamination Procedures
Appendix F: Glossary

Click here to see specific pictures of Brown Recluse Spider Bites.


Spider Bite on AnkleSpider bite on the ankle of a middle aged woman; 48 hours old.
The spider was killed and thrown away. This could have been a Brown Recluse bite, but the only way one can be for sure is to capture and identify the spider. This is a typical beginning stage of an ulcerating lesion. This wound needs to be debrided and cleaned thoroughly. Antibiotics are helpful to prevent infection. Close monitoring and follwup is a must to make sure the ulcer does not expand.


This spider bite is believed to be caused by a jumping spider. It is not uncommon for vesicles to appear in the vicinity of the bite area.

Jumping Spider Bite

Spider information

There are more than 34,000 different species of spiders worldwide. However, there are only a few dozen spiders that cause fairly pronounced envenomations in human beings. All spiders are poisonous. However, all cannot pierce the skin, and all do not have significant amounts of venom that cause skin lesions or systemic illness in humans. Spiders have long been a major cause of fears and phobias. The media has not done the spider population any favors, and have always portrayed them as evil creatures, dating back to the early days of film. It is somewhat surprising that something so small can cause such great fear. However, when one looks at an arthropod with eight eyes and eight legs that can also run very fast, one can easily understand how fears and phobias can develop.

Many spiders are capable of wind-blown disbursal. This is called ballooning. It gives us some understand how spiders have been found on even isolated islands.

Spider anatomy

The anatomy of an arthropod is segmented into two body parts, the cephalothorax, which is the head and the upper torso, and the abdomen. They have eight legs and the pedipalp, frequently mistaken for fangs, is actually used to hold prey. Fangs are usually tucked in, and therefore difficult to see.

Spider bite appearance/assessment

Spider bites can only be diagnosed if an individual brings in the spider itself, or even crushed parts of the spider. Beyond that, a diagnosis is based on clinical assumptions and a good history. A spider bite is often confused among healthcare providers with a variety of other illnesses including bacterial infection, viral infection such as herpes, Lyme disease, and bites of other insects. Treatment by the patient prior to coming in can mask the appearance. Many individuals will use Neosporin, and individuals who have an allergic response to the Neomycin in the Neosporin can have a very red and inflamed area, which on the surface makes the bite look much worse then it actually is. A thorough history is very important. Where have they been in the last week? Have they been indoors or outdoors? When did the patient first notice the bite? Does it itch? Does it burn? Have they recently traveled to another area of the country? All of these questions are important, when trying to diagnose a spider bite. Multiple bites are rarely caused by spiders, as generally spiders usually only bite once. A typical spider usually has a vesicle, and within 24-48 hours, it may or may not necrose, meaning the skin tissue in the center may start to become friable and die. It is also not uncommon to see satellite vesicles, which are small blisters away from the main bite site. These can be anywhere from a few inches to a foot away from the main bite site. Necrotic arachnidism is a term given specifically to the bite of a brown recluse spider. This refers to the ulcerative type lesion that usually accompanies the spider bite, which has gotten an enormous amount of press in the last few years. The venom of a brown recluse is primarily comprised of proteins and enzymes that actually cause some platelet disruption and tissue damage. Rarely do these bites cause death. However there have been reports in young children and the elderly. If there is going to be systemic effects, which are generalized effects, they will usually occur within the first 3 days of the bite, and individuals will experience nausea, fever, chills, and generalized muscle aches.

Spider Bite Treatment

Healthcare provider/medical treatment
Treatment is mostly supportive. If the healthcare provider feels there is a secondary infection, then antibiotics should be given. Those that cover staph and strep are highly advised. Surgical debridement of the wound can be very helpful, cutting back to clear clean margins and wet to dry dressings have been very effective. Treatment such as localized electrical shock, i.e. stun guns, hypobaric oxygen chambers, have all been found to be useless, and can create more damage, despite what you may see on other websites. There is no brown recluse anti-venom that is commercially available at this time.

It is important to note that in May, 2002, American College of Emergency Physicians contained an article about new methods for detecting brown recluse spider venom. This is important because accurately diagnosing a brown recluse bite definitely impacts treatment. As per the article, one of the most famous misdiagnoses occurred in New York with a 7-month old who contacted cutaneous anthrax, but who was initially diagnosed with a brown recluse spider bite. In a study at the University if Michigan by a team of emergency medicine investigators found early evidence that invasive biopsies are not necessary and, in fact, the Loxosceles ELISA assay was able to find brown recluse venom in hair samples. However, testing must occur at least 7 days after the initial envenomation. Since the vast majority of spider bite diagnoses, specifically brown recluse spider bites, are difficult to diagnose since the spider is not brought in, this would be a beneficial test, to ascertain the etiology of the skin lesion.1

1American College of Emergency Physicians, New Methods for Detecting Brown Recluse Spider Venom, May, 2002,


1. Emergency Medicine, A Comprehensive Study, Tintinalli, Judith, Kelen, Gabor, Stapczynski, Stephen, J.
2. Wilderness Medicine, Auerbach.

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