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Genus Loxosceles - Brown Spiders

Desert Recluse? - Loxosceles Brown Recluse - Loxosceles reclusa - female Which recluse? - Loxosceles Brown Recluse - Loxosceles reclusa - egg sac.2 - Loxosceles reclusa Unknown recluse species - Loxosceles - male Black widow or fake? - Loxosceles reclusa Loxosceles reclusa  - Loxosceles reclusa - female Loxosceles sabina? - Loxosceles arizonica
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Araneae (Spiders)
Infraorder Araneomorphae (True Spiders)
No Taxon (Synspermiata)
Family Sicariidae
Genus Loxosceles (Brown Spiders)
Other Common Names
Violin or Recluse Spiders
Explanation of Names
Loxosceles is from a two-ending Greek adjective meaning 'with slanting legs'. The presumably refers to the fact the legs are slighly laterigrade. Cameron(2005)(1)

Violin or Fiddleback Spiders because some species have a violin-like mark on the top of the cephalothorax.
Recluse spiders because of their shy nature.
There are 11 native species found in the United States:
L. kaiba
L. martha
L. palma
L. russelli
L. sabina

There are two species of brown spider that are occasionally introduced into the U.S:
L. laeta
Body is 6 - 12 mm long
Most are brownish or yellowish. They have six eyes in three pairs (This image shows the eye arrangement of brown spiders) The top of the cephalothorax is rather flat and has a lengthwise furrow along the midline at the rear third. Each foot has two claws.
In the US:
Brown spiders are occasionally transported outside of their range on or in furniture, boxes, and plants.
These spiders spin small, irregular webs underneath bark and stones.
Brown spiders are nocturnal, therefore most likely encountered at night when they are foraging for food. During the day they hide in secluded places.
Brown spiders will not bite unless provoked.
Little is known about the venom and bite of the lesser-known species of brown spiders.
“Although there are suspected variations in virulence among the species, all Loxosceles spiders should be considered potentially capable of producing dermonecrosis to some extent.” (Arachnids Submitted as Suspected Brown Recluse Spiders (Araneae: Sicariidae): Loxosceles Spiders Are Virtually Restricted to Their Known Distributions but Are Perceived to Exist Throughout the United States by Rick Vetter)

Loxosceles venom is cytotoxic to humans.(1)
See Also
Adult male Kukulcania spp. wander and are often mistaken for brown spiders, even (and likely especially) in FL where Loxosceles do not occur naturally. Immature Kukulcania spp. may have similar to identical coloration.
Print References
Milne, page 874 (2)
Borror et al, page 106 (3)
Internet References - An Approach to Spider Bites: Erroneous Attribution of Dermonecrotic Lesions to Brown Recluse or Hobo Spider Bites in Canada: Rick Vetter, MSc. and Robert Bennett, MSc, Ph.D. An interesting article (PDF format) about necrotic spider bites, their frequency of occurrence, and the frequency of misdiagnosis. Although this deals with Canadian data, it is very insightful about necrotic spider bites in the US also.
Works Cited
1.Spiders of North America: An Identification Manual
D. Ubick, P. Paquin, P.E. Cushing and V. Roth (eds). 2005. American Arachnological Society.
2.National Audubon Society Field Guide to Insects and Spiders
Lorus and Margery Milne. 1980. Knopf.
3.Borror and DeLong's Introduction to the Study of Insects
Norman F. Johnson, Charles A. Triplehorn. 2004. Brooks Cole.