Brown Recluse Spiders in Colorado: Recognition and Spiders of Similar Appearance Fact Sheet No. 5.607 Insect Series|Home and Garden by W.S. Cranshaw* Brown recluse and related recluse spiders Quick Facts (Loxosceles spp., Family Sicariidae) are, by far, the most commonly misidentified spiders • Colorado has many kinds in Colorado. Unfortunately, also greatly of spiders that are brown overdiagnosed are purported spider bites or have patterning that may caused by brown recluse spiders – a situation resemble brown recluse perpetuated by many in the Colorado spiders. medical establishment as well as through self-diagnosis. • The quickest way to positively Colorado hosts a great many kinds identify a recluse spider is to examine the arrangement of of spiders that are brown or have some Figure 1: Brown recluse spider. (Photo courtesy of patterning that may superficially resemble the University of Nebraska.) the eyes – there should be brown recluse spiders. However, close three pairs. examination can readily distinguish them (see Table 1). • Brown recluse spiders usually have a “violin pattern” on the cephalothorax. Identification • Funnel weaver spiders and The quickest way to positively identify if a spider might be a recluse spider is to examine wood louse hunters are the the arrangement of the eyes. This requires two groups most commonly some magnification. Recluse spiders have mistaken for recluse spiders. three pairs of eyes, a very unusual feature among spiders. Overwhelmingly, most spiders found in Colorado have four pairs. The arrangement of the eyes on the recluse Figure 2: Brown recluse spider. (Photo courtesy of spiders is one pair in the front, the other two Lisa Ames.) along the sides, forming a semicircle. Overall body color is brown, which may range from a light to dark brown. The abdomen is uniformly colored, without patterning. On the cephalothorax (the body region including the head and legs) a brown marking is usually present. This is typically described as a “violin pattern” and the eyes are incorporated into the base of it. The contrast intensity of this pattern can vary among the different recluse species and life stages. (Brown patterning on the cephalothorax also occurs in many Colorado Figure 3. Brown recluse spider showing the violin spiders, including funnel weavers and pattern on the cephalothorax. (Photo courtesy of cellar spiders.) Lisa Ames.) ©Colorado State University Legs of recluse spiders are long and Extension. 2/08. Revised 12/12. thin. The legs have a silky appearance, covered with fine hairs and large spines are www.ext.colostate.edu not present. The legs are uniform in color, *W. Cranshaw, Colorado State University Extension never banded. entomology specialist, and professor, bioagricultural sciences and pest management. 12/2012 Table 1. Features to identify recluse (brown) spiders (Loxosceles species). Eyes 3 pairs, of approximate equal size, arranged in semicircular pattern. Cephalothorax Overall color uniformly brown; Darker brown pattern in center, somewhat resembling a violin, usually present. Abdomen Overall color uniformly brown, without any patterning. Legs Uniformly colored, without any banding or patterning; Silky appearance due to fine hairs; no spines present. Activity Active at night; restricted to web-lined refugia during day. Webs Webs are not produced in open areas where they are readily seen. Recluse spiders are active at night. known of the recluse spiders found in the Figure 5: Female funnel weaver spider, During the day they hide in dark crevices U.S. is the brown recluse, Loxosceles reclusa. Agelenopsis sp. and hollows. In areas of the U.S. where It occurs in many of the midwestern they are common, recluse spiders found in and south central states, and can be very homes are often found in basements. common in and around homes in eastern Kansas, Missouri, Arkansas, Louisiana, Oklahoma, parts of Texas, and some other Recluse Spiders states. Occasionally it is transported out of in the United States its normal range, but it rarely survives and There are 10 native recluse spiders establishes outside the area. (Loxosceles spp.) in the U.S. with most Most, if not all, of the recluse spiders confined to areas of southwestern states have venom that can cause tissue death bordering Mexico. In addition, the (cytotoxins). Nine protein fractions Mediterranean recluse, Loxosceles rufescens, have been identified in the venom with is occasionally introduced and likely now most attention given to the enzyme Figure 6: Male funnel weaver spider, Agelenopsis sp. established in many parts of the country, sphingomyelinase D, considered the main although nowhere is it considered to be contributor to cell injuries resulting from common. The South American species L. bites by these spiders. laeta is established in a few localized areas The amount of venom introduced on both coasts. during a bite, and possibly the toxicity Identification of the various Loxosceles of the venom, varies among the recluse to the species level can only be done by spiders. For example, the medical an expert. Specimens of Loxosceles that importance of the brown recluse is well are collected from Colorado currently can documented in the literature. However, be identified by personnel at the Denver it has been suggested that bites of the Museum of Nature and Science. The best common South American species, Figure 7: Cellar spider, side view. Figure 8: Cellar spider. (Photo courtesy of the University of Nebraska.) Figure 4: General distribution of Loxosceles spiders in the United States. (Created by Rick Vetter.) and sensitivity to touch. This can further strain can result in lesions similar to those expand exposing underlying tissues as caused by bites of Loxosceles reclusa. the dead cells slough away. This ulcerated area is dry, since capillaries are sealed by the effects of the venom, but it may take a Colorado Arachnids couple of months to heal with permanent Mistaken for Brown scarring sometimes produced. Recluse Spiders Several spiders found in Colorado – and Recluse Spiders some other arachnids – are commonly in Colorado mistaken for brown recluse. These include the following: The brown recluse, and all other recluse Funnel weavers (Agelenidae). The Figure 9: Dysdera crocata, the ‘roly-poly hunter. spiders, are extremely rare in Colorado. funnel weavers are an extremely common, Confirmed specimens at the Denver brown-colored spiders. They get their Museum of Nature and Science collection name from the web they produce, which include only one specimen of Loxoceles is densely constructed of silk to produce a reclusa collected from the state (Boulder mat with a funnel-like retreat area where County, 1996). Also on record are four the spider normally rests. These webs can specimens of the Mediterranean recluse, L. rufescens (Denver, Bent, and Las Animas counties plus one from Larimer County Table 2. Medical conditions with symptoms located at the Colorado State University sometimes confused with brown recluse collection) and a single collection of L. spider bites (adapted from Vetter 2000). apachea (Larimer County). Bacterial Clearly incidence of these spiders • Methicillin-resistant Staphylococcus Figure 10: Running crab spider, Philodromus sp. aureus (MRSA or false spider bite diagnosis) in Colorado is incidental, resulting • Other Staphylococcus infections from occasional transfers coming from • Streptococcus infection L. laeta, are potentially even more chronically infested areas of the country. • Gonococcal arthritis dermatitis • Cutaneous anthrax dangerous. Conversely, only very few Establishment and sustained breeding of Reaction to drugs cases of complications are reported from these spiders in Colorado is much rarer, if it • Warfarin poisoning the ubiquitous Mediterranean recluse occurs at all. (There are two fairly credible Viral (L. rufuscens) and the native southern reports of some species of Loxosceles • Infected herpes simplex California species, L. deserta, suggesting established in a basement area; one each • Chronic herpes simplex • Varicella zoster (shingles) that these are less important medically. in Pueblo and Prowers counties. The Arthropod-induced The remaining species of native Loxosceles species involved have not been recorded • Lyme disease species that occur in North America do and the infestations were isolated to a • Rocky Mountain spotted fever not appear to be associated with serious single building.) • Ornithodoros coriaceus bite (soft tick) • Insect bites (flea, mite, biting fly) medical problems. Despite the near total lack of Loxosceles Fungal spp. spiders in Colorado, dermonecrotic • Sporotrichosis Symptoms of Brown lesions are commonly diagnosed • Keratin cell mediated response to fungus (misdiagnosed) as spider bites and, more Topical Recluse Bite specifically, as resulting from the bites of • Poison ivy/poison oak • Chemical burn Brown recluse bites initially may be felt recluse spiders. Other, more likely, causes Lymphoproliferative disorders as a slight pinprick – or not noticed at all. for such dermonecrotic lesions, and causes • Lymphoma The majority of bites result in no further that have been misdiagnosed as spider • Lymphomatoid papulosis effects. Even if bitten, spiders may not bites, include bacterial infections from Underlying disease states introduce any venom which results in a Staphylococcus or Streptococcus strains; • Diabetic ulcer dry bite. viral infections, particularly herpes or Vascular disorders • Focal vasculitis In a small percentage of cases, an shingles;