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 its carapace.

Species are often named after some of their traits. A person living in recluse prefers to hide away from attention and the same is the case with the brown recluse spider; it prefers not being disturbed by humans.

Description

The spider is brown to golden brown. Its size ranges from 0.25 inches to 0.75 inches, but it may grow larger. 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 picture section there's plenty of pictures of the brown recluse spider.

Bites

The spider is not aggressive and only bites if attacked or pressed against skin, threatened in any other way - or perhaps injured. Even though most people will try to avoid the brown recluse spider, bites occur from time to time. Loxoscelism refers to the condition produced by envenomations caused by the brown recluse.

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 (2008) no effective therapy for brown recluse bites ². Luckily, brown recluse spiders are more peaceful than most people believe.

No conclusive test for identifying envenomations caused by the brown recluse spider are available ³ -, and because loxoscelism can look like many serious types of pathologies, clinicians have to be very careful in their diagnosis of injuries.

Life Cycle

Eggs are deposited in sheltered areas and in off white egg sacks. The eggs have a diameter of about 0.3 inches and contain 40 to 50 eggs. Spiderlings molt five to eight times before reaching the adult stage. The molted skin looks very rigid in its structure, and can be used for identification by entomologists. The brown recluse spider can reach an age of two to four years.

Habitat

The Brown Recluse inhabit the south and south-central states from Georgia through Texas and north to Wisconsin. It is common belief that there are no brown recluse spider populations in neither California or Florida. Unfortunately, this may be about to change for California, as reports about individual brown recluse spiders found in California are heard more and more often. There are some loxosceles species populations found in California; these are the L. laete (Chilean recluse), L. deserta (desert recluse), L. russeltii (Russel's recluse) and L. palma (Baja recluse). It remains to be proven that there are any populations in California. Individual brown recluse spiders are also found in Florida from time to see. However, this is less often than in California, and the chances of being bit by a brown recluse spider in Florida is approximately nil.

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 its 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.

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 have been due to some imported specimens or misidentification or serious bites wrongly attributed to the brown recluse.

There is no scientific evidence suggesting that the brown recluse spider is expanding across the US - see also Rick Vetter and his webpage about brown recluse spiders and their whereabouts.

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

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.

It is 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 for instance similar in appearance when it comes to the markings on their backs but are more 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.

Another thing to look at is its legs. The brown recluse spider has uniformly colored legs in a light color with no bands or stripes. Its abdomen is also uniformly colored.

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.

Venom

The venom from a brown recluse spider is extremely venomous. Because of its venom the brown recluse spider is perhaps considered one of the most medically important groups of spiders. Envenomations can result in dermonecrosis and sometimes general systemic illness that can be life threatening for especially elderly and children.

Lesion caused by the venom results from direct effects of the venom. The venom has an effect on both a cellular and extracellular level. The effect depends on multiple factors that are not quite well understood. This is also why no curing therapy is available.

To help patients suffering from loxoscelism or bites from recluse spiders other treatment methods are however applied. Unfortunately they are not able to prevent someone from dying from brown recluse spider bites from time to time.

Loxoscelism

The term loxoscelism refers to the condition caused by a envenomations from spiders of the genus Loxosceles.

Brown recluse spiders are able to cause necrotic injuries on skin due to an enzyme named sphingomyelinase D found in the spider. Sphingomyelinase D is also found in several types of bacteria so damages caused by bacterial infections can resemble damages caused by the spider.

Associations between skin injuries of the dermonecrosis type (flesh-eating disease) and Loxosceles was first made in the late 19th century. The first scientific proof of a connection was made as late as 1947. Since then scientist has tried to treat patients with dermonecrosis but no effective therapy has yet been found.

Other web resources about the brown recluse spider

Kentucky Entomology
Living With Bugs
Arachnology
Burke Museum
Brown Recluse Spiders - LivingWithBugs
Spider Photographs by Peter J Bryant
Brown spider
Flora & Fauna in the Kaweah River Delta Region

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

You can contact me on the e-mail given here

Acknowledgements

Thanks to Thomas, Carolyn and David for giving me the permission to use their photos.

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