Brown Recluse Spider

The Latin name of the brown recluse spider is Loxosceles reclusa. It belongs to a group of spider also known as fiddleback spiders or violin spiders due to a dark fiddle shaped (or violin shaped) pattern on the dorsal side of their carapace.

When giving name to species it is common to name the species after some of it traits. A person living in recluse prefers to hide away from attention and the same goes with the brown recluse spider; it prefers not being disturbed by humans.

The spider is not aggressive and only bites if attacked or pressed against skin or in any other way threatened or perhaps injured. Even though most people will try to avoid the spider, bites occur from time to time.

The Brown Recluse inhabit the south and south-central states from Georgia through Texas and north to Wisconsin. There's no brown recluse spider populations in neither California or Florida. Individual specimens are however transported to California and Florida from time to time, but they don't propagate.

Bites may vary in severity from no symptoms at all to very severe reactions such as renal (kidney) failure and ultimatively death¹. Unfortunately there's currently (2006) no proven effective therapy for brown recluse bites ².

No conclusive test for identifying envenomations caused by the brown recluse spider are available³ - and because loxoscelism can look like many serious types of pathologies, clinicians have to be very careful in their diagnosis of injuries.

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Description

The spider is brown to golden brown. Its size is from 0.25 inch to 0.75 inch but may grow larger in some cases. It has short hairs on its body. The brown recluse spider has six eyes arranged in three pairs, which is less than he usual eight eyes found in most spiders. Males and females are similar in appearance while younger specimens are a bit lighter in their color. In the photo section there's plenty of photos of the brown recluse spider.

Life Cycle

Eggs are deposited in sheltered areas and in off white egg sacks. The eggs have a diameter of about 0.3 inch and contain 40 to 50 eggs. The egg sack is white. Spiderlings molts five to eight times before adulthood. The molted skin looks very rigid in their structure and can be used for identification by experienced entomologists. The brown recluse spider can reach an age of two to four years.

There's a lot of discussion going on about the distribution of the spider. Some will say that it's confined to a few states in the southern parts of the midwest while other says it can be found in all the following states: Texas, Nebraska, Kansas, Iowa, Missouri, Oklahoma, Tennessee, Alabama, Georgia, Missisippi, Louisiana, Kentucky, Ohio, Arkansas, West Virginia, Indiana, Illinois and West Virginia. When I write this some might say that it is probably not true and the specimens found in places like Ohio and West Virginia are not endemic to these areas, not a part of a thriving population - and must have been transported there somehow.

Habitat

In some of these states it will only occur in a confined area and in small populations. Bites from the brown recluse have also been reported from both Florida and California. This might be due to some imported specimens but more likely it is due to misidentification of the bite. A recorded population of the spider has neither been observed in Florida nor California. However there are some other Loxosceles spiders found in the eastern California desert, but this is not the brown recluse or Loxosceles reclusa.

Fig 1. Occurence of some Loxosceles species in the USA.

However there are some other Loxosceles spiders found in the eastern California desert, but it is not the brown recluse.

The name recluse means that it prefers to hide whenever possible and any place which have been undisturbed for some period. It is most often found in barns, woodpiles or beneath anything lying on the ground. It's also found in basements or garages behind boxes, in old clothing or inside papers, tires.

Its almost impossible to prevent the brown recluse as well as other spiders from migrating indoor. The best way for minimizing the risk of encountering the brown recluse spider indoor is to seal holes and cracks in the house and to keep debris and other material away from the foundation of the house.

Identification

It can be difficult to determine whether or not a spider is a brown recluse spider. Wolf spiders are similar in appearance when it comes to the markings on its back, but wolf spiders are hairy and generally larger than the brown recluse. The best way to identify a brown recluse spider is to look at its eyes. If it only has six eyes it's probably a recluse.

Misidentification of spiders as a brown recluse spiders are killing thousands of spiders every year, as people, understandably, won't take any chances with a possible brown recluse.

In general the toxicity of spiders is much less than what people tend to think. Ed Nieuwenhuys has done an excellent review⁶ concerning the myths about the toxicity of venomous spiders.

Other resources

Kentucky Entomology
Brown Recluse Spider @ LivingWithBugs

References

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 Volume 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 Vol. 21 (4): 191-193 (2006)
⁶ Ed Nieuwenhuys: The demystification of the toxicity of spiders