Louisiana Brown Recluse Distribution Study

Unlike other medically important spiders, the bite of brown recluse spiders can be initially painless, complicating the physician’s ability to determine whether skin lesions are the result of unwitnessed envenomation or another medical process. [1] 

Although published distribution maps for the United States exist, the information available for each state varies from very detailed (county by county documentation) to extremely poor (oral history of local arachnological professionals). [2]  In the southeastern quadrant of the United States, detailed brown recluse distribution maps have been developed only for Georgia [3], and the scarcity of specimens has been demonstrated for Florida [4] and South Carolina [5].  Although brown recluse spiders are well documented in northern parts of Mississippi, Alabama, and Louisiana, there are no definitive publications documenting its fine-grained presence in any of these three states.  Verification of this medically important arachnid will provide information with regard to the probability that a wound is from spider envenomation.  Patients outside of the known distributions are unlikely to have wounds resulting from spider venom.[6]  Thus, these maps may speed the diagnosis and treatment of alternate diagnoses such as community acquired MRSA or skeeter syndrome.  An additional benefit is the ability to reassure patients who are understandably concerned about the progression of wounds from spider envenomations based on the extreme images of necrotic arachnidism available on the internet. 

The entire state of Louisiana is currently within the published range of the brown recluse spider, although there is a recognized gap in our knowledge of the distribution within the state. [2]  Range assessment of the recluse spiders is made challenging by the difficulty in identifying the species of spiders that may be present.  For example, the invasive Mediterranean recluse has appeared in many cities around the world, and can be difficult to distinguish from the more toxic brown recluse spiders without dissecting the specimen.[6] It is not known if this species, or any other recluse species, is common in Louisiana.

In order to develop a reliable map for this state we began the Louisiana Brown Recluse Distribution Study in April 2009.  Our team on this project consists of two arachnologists (R Vetter and M Hodge) and two medical entomologists (M Fox and J Carlson).  Submissions of spiders from around the state are needed.  Physicians can play an important role in soliciting specimens.  Despite their name, brown recluse spiders are semi-communal, so that patients with recluse bites should be able to find these spiders in their homes.[6] 

We request that any spider suspected of being a recluse spider be mailed to:
John C. Carlson/Medical Ecology Group
Tulane University, Department of Allergy and Clinical Immunology
1430 Tulane Ave.  SL 57
New Orleans, LA  70115

Specimens can be alive or dead. Please see our suggestions for mailing specimens.  Questions by e-mail are welcome at venom@tulane.edu. 

1. Vetter RS, Isbister GK. Medical aspects of spider bites. Annu Rev Entomol. 2008;53:409-29.
2. Vetter RS.  Spiders of the genus Loxosceles (Araneae, Sicariidae); a review of biological, medical and psychological aspects regarding envenomations.  J Arachnol 36:150-163.
3. Vetter RS, Hinkle NC, Ames LM. Distribution of the brown recluse spider (Araneae: Sicariidae) in Georgia with comparison to poison center reports of envenomations. J Med Entomol. 2009 Jan;46(1):15-20.
4. Vetter RS, Edwards GB, James LF. Reports of envenomation by brown recluse spiders (Araneae: Sicariidae) outnumber verifications of Loxosceles spiders in Florida. J Med Entomol. 2004 Jul;41(4):593-7.
5. Frithsen IL, Vetter RS, Stocks IC. Reports of envenomation by brown recluse spiders exceed verified specimens of Loxosceles spiders in South Carolina. J Am Board Fam Med. 2007 Sep-Oct;20(5):483-8.
6. Vetter RS. Arachnids submitted as suspected brown recluse spiders (Araneae: Sicariidae): Loxosceles spiders are virtually restricted to their known distributions but are perceived to exist throughout the United States. J Med Entomol. 2005 Jul;42(4):512-21.