The brown recluse spider ( Loxosceles reclusa) is a member of the Sicariidae family and is one of the North American spider trio with medically significant venom. These spiders, also known as violin spiders, fiddleback spiders, or brown fiddlers, are known for their necrotic venom. Despite their potentially harmful bite, brown recluse spiders play a role in controlling populations of destructive and invasive insects.
Physical Characteristics and Identification
Brown recluse spiders are relatively small, with adults reaching up to 0.79 inches (20 mm) in body length. When the legs are extended, adults are usually about the size of a quarter, although size can be variable. Their coloration ranges from tan to dark brown. A key identifying feature is the dark brown violin-shaped marking on the cephalothorax, the body part to which the legs attach, with the "neck" of the violin pointing towards the abdomen. However, this characteristic is not a reliable diagnostic feature.
A more definitive diagnostic feature is the eye pattern. Most spiders have eight eyes, but the brown recluse spider has six eyes arranged in three groups of two eyes (dyads) in a semicircular pattern. They lack any stripes, bands, or mottling, and their legs are long and thin, uniformly colored with no spines.
Habitat and Behavior
The brown recluse is native to and found throughout the central and southeastern regions of the United States. They are synanthropic, meaning their populations benefit from living among humans. In nature, brown recluse spiders can be found under rocks, logs, woodpiles, and debris. They build irregular webs (no apparent pattern) in dry, dark, undisturbed places such as woodpiles, sheds, closets, or garages.
Indoors, they seek shelter in basements, cardboard boxes, storage closets, laundry left on the floor, and shoes. They are commonly found in houses and are considered synanthropic, meaning their populations benefit when living among humans. They are attracted to homes because there are hiding places and prey to eat. They get into homes through crevices or cracks in foundations or around doors, vents, or under eaves or soffits. People may even carry these spiders into residential buildings in boxes, furniture, and other items. They have adapted well to living indoors. In homes, they are found in areas without air conditioning or ventilation, such as near a furnace or water heater, in the bathroom behind a toilet or tub, and in the basement or under stairs. They are also found in cluttered storage areas and closets, under furniture and folded bedding, and in any other cluttered areas where it is dry and warm. They are also commonly found in storage boxes, shoes, coats, stored clothes, and drawers.
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Brown recluse spiders prefer to be secluded in dark areas away from human activity during the day. At night they come out to search for food. Unlike most spiders that stay near the web, the Brown Recluse leaves its web at night to hunt. They are active in temperatures between 45 degrees F and 110 degrees F.
Diet and Feeding Habits
Brown recluse spiders are carnivores with a diet consisting mainly of insects. They are partly opportunistic, preferring to hunt for live prey but also consuming dead insects, especially those recently killed. Brown Recluse spiders prefer a diet consisting of pests such as cockroaches and other small insects. Some foods that brown recluse spiders eat: crickets, cockroaches, moths and flies. They will easily consume their prey dead or alive, as they are not picky eaters.
They are also known to be cannibalistic and may consume other brown recluse spiders, even of their own species. This indicates they’re carnivores. They are partly opportunistic. Namely, while they prefer hunting for live prey, they won’t refuse a dead one, especially if it has been recently killed.
Brown recluse spiders hunt for food during the night. They are nocturnal hunters, making them less likely to be out during the day and don’t kill their prey with webs. They are known for biting their prey, infecting it with venom, and leaving the area, returning to eat it only after it dies. The purpose of their venom is to subdue their prey.
Interestingly, brown recluse spiders can go months without hunting and eating. The longest documented period of a brown recluse spider not touching any food was two years. This is because the species can stay in one spot for prolonged periods, conserving energy and waiting for prey to enter their perimeter. They are able to eat scarcely because they can stay in one spot, not burning calories and store those nutrients when they eat.
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Unlike some spider species that use their webs to ensnare their prey, brown recluse spiders are nocturnal hunters. They chase down their victims.
Life Cycle and Reproduction
The life of a brown recluse spider starts with a silky egg sac, usually laid in summer. Females lay about forty to fifty tiny yellow eggs inside a sticky silken sac less than an inch in diameter. A female can produce several sacs and up to 300 eggs during the summer. The Brown Recluse egg sac is off-white in color, about 1/3" in diameter, and generally contains about 50 eggs per sac. Females produce about 5 sacs in a lifetime.
After hatching from their eggs, baby brown recluse spiders will stay close to their mother for a couple of weeks. The mother is also responsible for feeding the youngsters with anything it can catch. The eggs hatch in about one month. The spiderlings molt five to eight times between 10 and 12 months to develop into adults.
Before brown recluses mate, there is usually a courtship ritual. Males use chemotactic senses to find a female. Males mostly rely on the fine sensory hairs that cover the body and appendages to locate a female. But along with the sense of touch, males also have the ability to distinguish various chemical substances. Through this combined chemotactic sense, males find their mate by a scent that she leaves on the threads of her web. Males must announce their presence as a potential mate or the female may mistake them as potential prey. Once the female submits to the male’s advances, mating takes place. The female later lays hundreds of fertilized eggs in a silk cocoon that she attaches to a web or plant. She may even carry it with her.
Predators
Like most spider species, the brown recluse spider has natural predators. Among these, we can mention the praying mantis, crickets, and especially blue jays. Their biggest natural predator, however, is the Homo sapiens.
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Brown Recluse Bites and Their Effects
Brown recluse spiders have an undeserved reputation of being aggressive spiders. They are not always aggressive and their bite is not always deadly. They only bite when crushed, handled, or disturbed. The brown recluse will typically only bite a human if it is threatened or touched. Brown recluse spiders are solitary.
A human’s reaction to the bite depends on the amount of venom injected and an individual's sensitivity to it-some people are unaffected, others may feel a pinprick, and others a stinging sensation followed by intense pain. The bite of a brown recluse spider will sometimes require medical attention. This means that the species is not deadly. However, you do have to treat the bite spot. Their bite can be mild to serious in humans, and their hemolytic venom is toxic.
Often, the initial bite is not painful, but the venom is a potent cytotoxin that may cause an enlarging necrotic sore that has difficulty healing. The cells surrounding the puncture die as a result of the toxin, producing a black gangrenous spot. In some cases, the bite produces a necrotic lesion, typically resulting in a flat or slightly sunken bluish patch with irregular edges, a pale center, and peripheral redness, often with a central blister. In rare instances, bites in the early stages induce systemic reactions accompanied by fever, dizziness, chest pain, nausea, or vomiting, particularly in children and older adults.
First aid for someone who has been bitten by a brown recluse spider includes the use of an ice pack to prevent or reduce the swelling in the area where the bite occurred. Cooling the area helps to lessen tissue damage and reduce burning sensation, pain, and swelling. Victims should promptly seek medical treatment from licensed doctors. If the spider can be found and identified as the likely culprit, it should be taken with the patient to the doctor. Even crushed or damaged specimens can usually be identified. Start by cleaning the area with water and soap.
Management and Control
Managing brown recluse spiders starts with knowing where they hide and how they behave. Once established in a home, brown recluse spiders are often difficult to control. They can take shelter in dry, dark, undisturbed areas, and many such places exist inside homes and buildings. Residents should take steps to prevent bringing pests home and keep homes clean and clutter free.
Keep storage areas clean and use sealed plastic bins instead of cardboard to prevent brown recluse spiders from settling in. Check for gaps around windows, doors, and vents and seal them. Shake out shoes and clothes that have been in storage. Eliminate spider harborages by decluttering closets and storage rooms and areas. Remove bed skirts to reduce the chances of spiders crawling onto the bed.
A thorough inspection with a bright flashlight to reveal the location and level of infestation is the first step in effective management. Inspection should focus on likely spider habitats. Indoors, look for spiders, egg sacs, and shed spider skins in undisturbed storage areas such as closets, crevices behind furniture and bed, behind hanging pictures, clothing, shoes, and especially storage containers and boxes. In an infested garage, attic, basement, or crawl space, search for signs along joists, sills, rafters, behind baseboards and woodwork, within ducts and registers, above suspended ceilings, and under rolled insulation. The person conducting the inspection should wear personal protective clothing such as gloves. Tape pant legs to shoes and shirt cuffs to gloves. To prevent spiders from crawling up pant legs, constrict the pants with rubber bands around the ankles.
Sticky spider traps and flat glue boards are excellent nonchemical ways to aid visual inspection. Besides being useful for detection, they can also catch and kill spiders, most likely the males and old juveniles. Position the traps in places where the spider is most likely to hide and forage. Professional pest control services can also use flushing agents as a monitoring tool to locate breeding areas. Remove any spiders and webs found by vacuuming so you can monitor potential spider activity in future inspections.
Exclusion is to deny the spiders access to homes and hiding places. Seal cracks and crevices in the structure where spiders may gain access to the house. Common areas for cracks and crevices are windowsills, door thresholds, and around pipes and vents. Improve ventilation in attics and crawl spaces.
Pesticides labeled for spider control are often required for serious brown recluse infestations. Enlisting the services of a professional pest control operator is an option to be seriously considered when chemicals are to be applied. Target applications on exterior and interior cracks and voids where the spiders are known or suspected to be feeding or hiding. Encapsulated formulations of residual pesticides and waterproof dust are good choices for spot treating spaces such as wall voids, cracks, crevices, behind shutters, baseboards, outlet covers, and under siding. Aerosol products can be sprayed directly on the spiders. All the chemicals kill spiders by direct contact. Applications must follow label instructions to minimize the risks and maximize the benefits.