The recluse spiders or brown spiders, also known as fiddle-back, violin
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