spiders or reapers, are a genus of venomous spiders known for their bite,

which sometimes produces a characteristic set of symptoms known as

loxoscelism. Recluse spiders are now identified as members of the family

Sicariidae, having formerly been placed in their own family, the Loxoscelidae.

Relation to other spiders Sicariidae are of the superfamily

Scytodoidea. Other families in the Scytodoidea include Drymusidae,

Scytodidae, and Periegopidae. Habitat and appearance

Loxosceles is distributed nearly worldwide in warmer areas. All have six

eyes arranged in three groups of two and some are brownish with a darker brown

characteristic violin marking on the cephalothorax. However, the "violin

marking" cannot be used as a reliable way to identify the spider as thousands

of species of spider have the same markings. Spiders come with many

markings varying greatly within the same species. Most Loxosceles can live for

one and a half to two years. Members of both genera can live for very long times

without food or water. They are about 7–12 mm long.

Familiar species in the United States include the brown recluse spider. It is

found in a large area of the Midwest, west to Colorado and the New Mexico

state line and east to northern Georgia. Sporadic records from other locations

only represent incidental introductions, not established populations. Other

notable members of this genus include the Chilean recluse spider and the

Mediterranean recluse spider. Recently, concerns have been raised

regarding recluses spreading faster due to warmer air carrying them farther as a

result of changing climate. On the contrary, newly hatched recluses do not

travel via ballooning and thus the populations are confined to very tight

spaces with dense populations. Venom components and effects

Loxosceles spiders, like Sicarius species, have potent tissue-destroying

venoms containing the dermonecrotic agent, sphingomyelinase D, which is

otherwise found only in a few pathogenic bacteria. Recent research has indicated

the venom is composed largely of sulfated nucleosides, though these

compounds are relatively new discoveries, so little is known about

them. The venom produces necrotic lesions that are slow to heal and may

require skin grafts. The wounds are also prone to infection. Rarely, the venom is

carried by the bloodstream to internal organs, causing systemic effects.

The venom is identical in male and female spiders, but females can have

almost twice the concentration of toxins. For unknown reasons, the

toxicity of the venom to mammalian species varies; recluse bites will cause

necrosis in humans, rabbits, and guinea pigs, but not in mice or rats.

The Chilean recluse supposedly has a more potent venom, which results in

systemic involvement more often. This spider was accidentally introduced to

the Los Angeles area. This spider, however, seems to be confined to a very

limited area, even though it has been known there for over 30 years. All

Loxosceles species that have been tested have venoms similar to that of the brown

recluse and all should be avoided. In general, though, they are not aggressive

and commonly occupy human dwellings without causing problems.

Many types of skin wounds are mistaken for or assumed to be the result of a

recluse spider bite. Several diseases can mimic the lesions of the bite,

including Lyme disease, various fungal and bacterial infections, and the first

sore of syphilis. It is important to associate the spider directly with the

bite to initiate proper treatment, and to consider alternative diagnoses if no

spider was seen. A recluse spider is usually found in the

center of its web, which often contains the remnants of prey items. The most

common food items for the Arizona recluse are night-active ants such as

carpenter ants. The brown recluse feeds on whatever small prey is available, and

has been observed to prefer scavenging over actively hunting.

Bites most often occur as a defense when the spider is trapped against the skin,

in clothing, for example. Insecticides often fail to kill the spider, instead

intoxicating its nervous system and inducing aggressive behavior.

The bite of a recluse spider can generally be categorized into one of the

following groups: Unremarkable - self-healing minute

damage Mild reaction - self-healing damage with

itchiness, redness, patterns of aggressive behavior and a mild lesion.

Dermonecrotic - the uncommon, "classic" recluse bite, producing a necrotic skin

lesion. About 66% of necrotic bite lesions heal with no complications. In

extreme cases, the lesion may be up to 40 centimeters wide, last for several

months, and heal with a permanent scar. Systemic or viscerocutaneous - an

extremely rare, sometimes fatal systemic reaction to envenomation of the

bloodstream. This reaction is more common in obese victims, because the

venom destroys adipose tissue. It is more often fatal in children.

Most bites are unremarkable or mild. Species

There are about 100 species of Loxosceles.

Species include: See also

List of Sicariidae species Spider families

List of spiders associated with cutaneous reactions

Chilean recluse Footnotes

External links Arachnology Home Pages: Loxosceles:

Recluse spiders Biodiversity Explorer: Family

Sicariidae. World Spider Catalog. 2014.

Vetter, R. 2003. Causes of Necrotic Wounds other than Brown Recluse Spider

Bites. Vetter, R. 2003. Myth of the Brown

Recluse Fact, Fear, and Loathing. Pictures of L. reclusa and wound