The brown recluse is a fairly nondescript, medium-sized spider, about 3/8-in. in body length. For many years, publications almost uniformly mentioned that the best way to identify a brown recluse spider is by a violin pattern on the dorsal surface of the cephalothorax (the body part to which the legs attach). Although this is basically true, because there are several other harmless house spiders that have similar markings, non-arachnologists frequently misidentify almost any brown spider found around a home as a brown recluse.
A more accurate method to identify a recluse spider is to count the eyes. Most spiders have eight eyes in two rows of four (or something approximating this). By contrast, recluse spiders have six eyes: a pair in front and a pair on either side, separated by a space. Without a magnifying lens, they will appear as three dots. Spitting spiders, genusScytodes, also have this eye pattern but typically look very different from recluses.
Another reason that the eye pattern should be used over the violin pattern is that the violin pattern is faint or missing in young or newly molted brown recluses — as well as in several other North American recluse species. Therefore, it’s likely for an actual recluse to be misidentified as harmless when, in fact, it could be dangerous.
The brown recluse spider is an urban pest. It is similar to pigeons, rats and cockroaches in that its numbers increase in association with humans. However, for unknown reasons, the other species found in the Southwestern deserts are not urban pests. They typically only infest homes that are surrounded by native vegetation, like cactus and creosote.