Know your pests

Brown Recluse Spiders

If asked to name all the spiders with which they are familiar, most Californians would have a short list: tarantula, black widow, and brown recluse. Tarantulas are well known because of their large, intimidating size and their use in many movies as eight-legged villains. Black widows are very common throughout the state, causing potentially serious injury with their bite. The adult females are easily identifiable by their shiny black body color and red hourglass on the belly. The brown recluse, however, is an enigma: there are no populations of the brown recluse, Loxosceles reclusa, in the state and fewer than 20 verified specimens have been collected over several decades in California. Yet in California people frequently relate stories in which they or someone they know was supposedly bitten or they have had a physician diagnose them with a brown recluse spider bite. However, there are several other species of recluse spiders that can occur in southern areas of California and that can cause similar medical concerns. This publication was written to provide science-based information about the status of the brown recluse and other related spiders in California.

COMMON AND SCIENTIFIC NAMES

Over the years, the group of spiders to which the brown recluse belongs has been known by various colloquial names: “violin” spiders, “fiddleback” spiders, “recluse” spiders, and “brown” spiders. The American Arachnological Society chose “recluse spiders” as the official common name for this group. The scientific name for the recluse spider group is Loxosceles (lox-SOS-a-leez) and rhymes somewhat with “isosceles” as in the triangle. Whereas “isosceles” means equal legs, “loxosceles” means slanted legs, referring to the way the spiders hold their legs at rest. All known members of the group have a scientific name, and the more familiar members of this group also have common names (e.g., brown recluse, desert recluse, Arizona recluse).

IDENTIFICATION

The most definitive physical feature of recluse spiders is their eyes: most spiders have eight eyes that typically are arranged in two rows of four, but recluse spiders have six equal-sized eyes arranged in three pairs, called dyads. There is a dyad at the front of the cephalothorax (the first main body part to which the legs attach) and another dyad on each side further back with a space separating the dyads from one another