Eleven species of recluse spiders are native to the United States and two non-natives have become established in certain highly restricted areas of the country. The brown recluse spider is the proper common name for only one species, Loxosceles reclusa. It is the most widespread of the North American recluse spiders and lives in the south central Midwest from Nebraska to Ohio and south through Texas to Georgia. Although the brown recluse does not live in California, we do have four species of native recluse spiders. The most common Californian recluse spider is the desert recluse, Loxosceles deserta. It is found mostly in the Sonoran and Mojave deserts, in the foothills of the lower San Joaquin Valley, and in adjacent areas of Mexico; most of these areas are sparsely populated by humans. In older literature, this spider was referred to as Loxosceles unicolor. There are additional species (Loxosceles russelli, Loxosceles palma, Loxosceles martha), but they are so uncommon that they are of scientific interest only.
In addition to these native species, the Chilean recluse spider, Loxosceles laeta (pronounced “LEE-ta”), has become established in portions of Los Angeles (Alhambra, Sierra Madre, Monterey Park, San Gabriel). This spider, however, seems to be confined to a very limited area in Los Angeles County even though it has lived there for possibly over 70 years (one specimen collected from Los Angeles in 1936 is housed in Chicago’s Field Museum spider collection). Also, occasional interceptions of the Mediterranean recluse, Loxosceles rufescens, are found in commercial goods shipped from out-of-state, but no populations of this spider are currently known in California.
Life History Characteristics
Recluse spiders, as their name implies, are reclusive. These nocturnal spiders emerge from their retreats at night and actively hunt down prey or may wait for prey to land in the small area several inches from their retreat. Although they do not build webs to capture prey, they do use silk to build a retreat in which they hide during the day. As dawn approaches, they may seek shelter in dark places such as in clothing or shoes. Also, mature males roam in search of females. It is these two behaviors that can bring them into contact with people.
In nature, recluses are found in cracks and crevices in and under rocks. Recluses have very much benefited from human-altered environments where they are readily found under trash cans, plywood, tarps, or rubber tires, in boxes, etc. They are synanthropic (found in association with humans) and therefore are considered “house” spiders. In fact, in South America the recluse species have common names that translate as “the spider behind the picture” or “the spider in the corner.”
Recluse spiders are relatively long lived. Among the various species, they mature after about 1 year and average a 2- to 4-year life span with some living more than 7 years under laboratory conditions. They are also well known for surviving long periods (6–12 months) without food before perishing.
Abundance of Recluses
One consistent life history characteristic of recluse spiders is that in the right environment their populations are usually dense. If you find recluses, you do not find one, you find many. The brown recluse spider, Loxosceles reclusa, is a common house spider in the midwestern United States. Examples for the brown recluse include 9 under a piece of plywood in Oklahoma, 52 in an indoor laboratory, 6 under a waterbed frame in Arkansas, 40 collected in a Missouri barn in 1 hour, 44 in sticky traps in a Tennessee home in 1 day, and eight Oklahoma 13-year-olds unknowingly hand-collected about 60 amongst bricks in about 7 minutes (without getting bitten).
In a mind-boggling study, in 6 months, a family in Kansas collected 2,055 brown recluse spiders in their 19th-century built home. They have lived there nearly a decade, continue to find brown recluse spiders regularly and only once in 10 years has anyone shown evidence of a bite; it was to a finger which turned red for a few days and then healed without incident. In fact, on many evenings, this family collected more brown recluse spiders per hour in their home than the entire California human population has ever been able to find in the state.
Similarly, for the desert recluse in California, 12 of these spiders were collected under a doghouse in Yucca Valley and six were removed from a cottage bedroom in the Mojave Desert. In a study in Chile, 645 of 2189 homes that were searched contained the South American recluse spider, Loxosceles laeta. The five most infested homes averaged 163 spiders and in none of these houses had spider bites been reported.
Non-abundance of Brown Recluses in California
Unlike many other spiders that disperse by either migrating or being carried by air currents when small (“ballooning”), recluse spiders can expand only outside their native range as a result of human intervention. The few brown recluses that have been collected in California typically are found in facilities that receive goods from out of state or are unintentionally transported by people who have moved from the Midwest. In these instances, searching the immediate area yielded no additional brown recluses so they were considered to be individual stowaways. Undoubtedly, more brown recluses have been inadvertently brought into the state via commerce and the relocation of household belongings; however, amazingly few specimens have ever been collected. Never have any of these trans located spiders been able to establish a foothold and start a population in California. Considering that brown recluse spider bites are not common in the south-central Midwest where brown recluses frequently cohabit with people, it is clear that California does not have anywhere near sufficient populations of these spiders to be responsible for the number of cases or illnesses that are attributed to them. The problem of misdiagnosis is widespread in North America, including such unlikely places as Alaska and Canada where doctors have attributed skin lesions to recluse bites when no brown recluse spiders have ever been found north of the 48 contiguous U.S. states.
Potential Toxicity of Bites
All Loxosceles spiders tested so far have the venom component that is capable of causing necrotic skin lesions, so it is best to assume that all recluse spiders may be capable of causing skin damage. In general, the desert recluse spider’s venom is similar to that of the brown recluse and should be considered of equal potency. In comparison to the brown recluse spider, the Chilean recluse supposedly has venom more potent and the Mediterranean recluse’s venom has been said to be less potent. However, these comparisons are more anecdotal than quantitive assessments.
About 10% of brown recluse bites cause moderate or greater tissue damage and scarring, but the vast majority heal very nicely without medical intervention. There is still not one proven death from brown recluse bite (a person was bitten by a spider caught in the act and properly identified). While there are several highly probable deaths reported in children, these are extremely rare occurrences, about one every decade or so.
RICE Therapy Rest, Ice, Compression, Elevation
The recommended treatment for most brown recluse bites (the ones that do not become traumatic) is simple first aid: RICE therapy.
- Rest
- Ice
- Compression
- Elevation
*Additionally, many people diagnosed as having brown recluse bites in California are treated with antibiotics. The recommended treatment for most actual brown recluse bites (the ones that do not become traumatic) is simple first aid: RICE therapy (Rest, Ice, Compression,
Elevation). Antibiotics work against bacteria and have no effect on spider venom. However, regardless of the causative agent, it is wise to seek medical attention if you feel that it is warranted.
*According to UCDAVIS IPM Web site
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