A brown recluse spider, Loxosceles reclusa.
Photo: Rick Vetter

Does this sound familiar?

You have decades of pest control experience working in a region that you know doesn’t have brown recluse spiders. In your career, you have never seen a brown recluse in any of your clients’ homes. However, you are called out to treat for recluse spiders because a local physician diagnosed one of the home’s occupants with a brown recluse bite. You are asked to control an invisible pest. You may try to educate (argue with?) your client because you know that you have better and more practical information on the distribution of these infamous spiders than does the local medical community and that there is a minuscule probability of finding recluses in the home, let alone being bitten by one.

Over the years, I have waged a crusade trying to educate the medical community as to their propensity to misdiagnose and overdiagnose brown recluse spider bites, especially in portions of North America where these spiders are not known to exist/have never been documented. I have also conveyed this information to the pest control industry for their benefit. In the medical literature (as in many other professions), when you try to identify something, you describe what it looks like. That makes sense of course. So, medical authors have described in the medical literature the signs and symptoms in patients in whom they diagnosed a recluse bite. (“Signs” are what the doctor sees; “symptoms” are what the patient tells the doctor: “unsteady walk” is a sign, “dizziness” is a symptom.)

However, a common component of medical diagnosis is the process of elimination where using atypical signs of a condition will exclude a particular medical condition and allow a physician to arrive at a more highly probable cause. With this in mind in regard to recluse bites, a recent publication in the Journal of the American Medical Association — Dermatology (JAMA Dermatology) has produced an acronym of NOT RECLUSE (see below), where each letter stands for a sign or situation which should exclude or minimize the chances of something being a recluse bite.

Author’s note: The information presented here is an educational tool to help the PCO in a situation where a client may disagree with your brown recluse knowledge or where a medical person needs to be better educated. A PCO should not be making diagnoses or telling a person what they do or do not have. The reason for presenting this article to PCOs is that when confronted with a scenario where a brown recluse bite is unlikely, you can offer this PCT article and/or the original JAMA article to your clients and suggest they take the information to their physician for a reassessment because there was no evidence of brown recluses in their home.

‘NOT RECLUSE’ ACRONYM. The hope is that this information will trickle down through the many branches of medicine with the end result being improved health care. The PCO can contribute to this by being aware of this article and the references at right and present them to educate customers where brown recluse bites are highly unlikely. Even in indigenous recluse areas like Kansas, Oklahoma and Missouri, recluse bites can be misdiagnosed so the NOT RECLUSE article may function well even where recluses do exist and bites are likely. One of the biggest dangers of a brown recluse bite misdiagnosis is that there are some medical conditions such as MRSA, necrotizing fasciitis and carcinomas that are much worse than a recluse bite would ever be (sometimes being fatal). An educated PCO adds another functional sentinel in getting it right.

Numerous: All spider bites are typically a last-ditch effort by a spider to defend itself as it is being seriously crushed. Therefore, recluse bites are typically singular lesions. Multiple, simultaneous lesions in one person or multiple family members, especially if they are widely spaced on different parts of the body, suggests an infection or an infestation by a blood feeder such as bed bugs or fleas, which are alternate pests that the PCO can look for instead of spiders. Ask your client if they sleep with their dog or cat.

Occurrence: Most recluse bites usually happen indoors in bed when a sleeping person rolls over on a spider in the night or presses a spider against flesh when getting dressed. Recluses are not known to occur in green vegetation. Lesions developing after exposure to gardens, natural areas or in grass are more likely poison ivy or a fungal infection called sporotrichosis caused when plant material causes a break in the skin.

Timing: In North America, recluses are active inside homes from about April to October. Lesions occurring from November to March are unlikely to be recluse bites. Even though homes are heated during winter, brown recluses respond to winter light cycles by becoming inactive. One exception may be exposure in December when unpacking holiday decorations.

Red center: Recluse venom immediately destroys the capillary network at the bite site so red blood cells can’t get in to provide oxygen. Therefore, the bite site will be white, purple or blue and not red.

Elevated: Recluse bites are typically flat or slightly sunken although there may be an initial blister at the bite site early on. If a lesion is elevated more than 3/8-inch from the normal skin level, then it is more likely an infection and not a recluse bite.

Chronic: Even the worst recluse bites heal by the three-month mark. Longer healing times would indicate some other condition.

Large: Most recluse bites do not get larger than 4 inches in diameter.

Ulcer formation early: Recluse bites typically develop an ulcer from 7 to 14 days post-bite. If an ulcer forms before that, it is probably a bacterial infection.

Swollen: Although recluse bites can cause major swelling above the neck and in the feet, significant swelling below the neck to the ankles is not typical in recluse bites. Major swelling in these other areas is probably a bacterial infection or maybe a wasp/bee sting.

Exudative: Recluse bites do not exude pus, serum or blood (except for possibly the initial blister at the bite site which may produce red-tinged fluid). The presence of pus indicates that the wound is most likely a bacterial infection like MRSA (methicillin-resistant Staphylococcus aureus) (Vetter 2005). Bacterial infections are the most common causative agent of skin lesions that are mistaken for brown recluse spider bites. In addition, although some medical authors claim that spiders COULD vector bacteria when they bite, several thousand reports of bites by many different species showed that bacterial infection is non-existent or extremely rare as a listed sign of envenomation (Vetter et al. 2015).

Rick Vetter is a retired arachnologist from the University of California, Riverside (UCR).

Stoecker, W.V., R.S. Vetter, and J.A. Dyer. 2017. NOT RECLUSE: A mnemonic device to avoid false diagnosis of brown recluse spider bites. JAMA Dermatology, in press.
Vetter, R. 2005. [They’re not] spider bites. Pest Control Technology 33(4): 86-88.
Vetter, R.S., D.L. Swanson, S.A. Weinstein and J. White. 2015. Do spiders vector bacteria during bites? The evidence indicates otherwise. Toxicon 93: 171-174.