By Anders Nielsen, Ph.d.
Brown recluse spiders belong to a group of spiders also known as fiddleback spiders or violin spiders. This is due to a dark violin shaped pattern on its back (its carapace). The brown recluse spider mostly avoids confrontation and attention; hence the recluse part of its name. Most bites are in fact accidents, as they are not aggressive towards humans.
The brown recluse spider is brown or golden-brown in color and ranges in length from 0.25 inches to 0.75 inches. It has six eyes positioned in three pairs, uniformly colored legs, and its second pair of legs longer than its first. Males and females are similar in appearance, while younger specimens have a lighter color.
The name recluse means that it prefers to hide whenever possible and in any place that has been undisturbed for some period. It is often found in barns, woodpiles, or beneath anything on the ground. It is also found in basements or garages behind boxes, in old clothing, or inside papers or tires.
It is almost impossible to prevent the brown recluse, as well as other spiders, from migrating indoors.
The best way for minimizing the risk of encountering the brown recluse spider indoors is to seal holes and cracks in the house and to keep debris and other material away from the foundation of the house.
The brown recluse inhabits the south and south-central states from Georgia through Texas and north to Wisconsin. In scientific circles, the consensus is that no populations are present in either California or Florida.
Unfortunately, some encounters with brown recluse spiders have been reported from areas where the spider is nonendemic (Ohio, Illinois, Florida, New York, and California). The reason for such meetings is misidentification of the brown recluse or no identification whatsoever. Some newspapers also take pride in making enticing headlines about fear and brown recluse spiders.
Some loxosceles species are found in California though. These are the Loxosceles laete (Chilean recluse), L. deserta (desert recluse), Loxosceles russeltii (Russel's recluse), and Loxosceles palma (Baja recluse).
Recluse spiders deposit their white egg sacks in areas offering shelter. The eggs have a diameter of about 0.3 inches, and each sac contains 40 to 50 eggs. Spiderlings molt five to eight times before reaching the adult stage. Molted skin has a very rigid appearance and is used for identification by entomologists. The brown recluse can reach ages of two to four years.
Because of its venom, the brown recluse spider is considered medically important. Envenomations can cause in dermonecrosis and ultimately systemic breakdown of body functions. The elderly and children should be careful.
The term Loxoscelism refers to the conditions envenomations from spiders of the genus Loxosceles causes.
Associations between skin injuries of the dermonecrosis type (flesh-eating disease) and Loxoscelism was initially proposed in the 19th century, but the first scientific proof of a connection was in 1947.
Multiple factors govern how the venom affects individuals. Antivenom is not available, which means that patients suffering from Loxoscelism have to handle the pain with painkillers.
Generally, the toxicity of spiders is less than commonly perceived. A better understanding of the role of venom throughout evolution is found in the review by Ed Nieuwenhuys6. The review addresses the myths about the toxicity of venomous spiders.
Associations between skin injuries of the dermonecrosis type (flesh-eating disease) and Loxoscelism was initially proposed in the 19th century but the first scientific proof of a connection was in 1947.
1 Dyachenko P et al., Epidemiological and clinical manifestations of patients hospitalized with brown recluse spider bite
2 Swanson DL et al., Loxoscelism CLINICS IN DERMATOLOGY 24(3) page. 213-221 (2006)
3 Wendell RP, Brown recluse spiders: A review to help guide physicians in nonendemic areas
4 Pauli I et al. The efficacy of antivenom in loxoscelism treatment TOXICON 48 (2): page 123-137 (2006)
5 ME Peterson, Brown Spider Envenomation CLINICAL TECHNIQUES IN SMALL ANIMAL PRACTICE 21 (4): 191-193 (2006)
6 Ed Nieuwenhuys: Spider toxicty demystified
Thanks to Thomas, Carolyn and David for giving me permission to use their images.
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