Brown Recluse Spider
The brown recluse spider or violin spider, Loxosceles reclusa, Sicariidae (formerly placed in a family “Loxoscelidae”) is a spider with a venomous bite.
Brown recluse spiders are usually between 6–20 mm (1⁄4 in and 3⁄4 in), but may grow larger. While typically light to medium brown, they range in color from cream-colored to dark brown or blackish gray. The cephalothorax and abdomen may not necessarily be the same color. These spiders usually have markings on the dorsal side of their cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing to the rear of the spider, resulting in the nicknames fiddleback spider, brown fiddler, or violin spider.
A brown recluse’s stance on a flat surface is usually with all legs radially extended. When alarmed it may lower its body, withdraw the forward two legs straight rearward into a defensive position, withdraw the rearmost pair of legs into a position for lunging forward, and stand motionless with pedipalps raised. The pedipalps in mature specimens are dark, quite prominent, and are normally held horizontally forward. When threatened it usually flees, seemingly to avoid a conflict, and if detained may further avoid contact with quick horizontal rotating movements. The spider does not usually jump unless touched brusquely, and even then its avoidance movement is more of a horizontal lunge rather than a vaulting of itself entirely off the surface. When running the brown recluse does not appear to leave a silk line behind, which at any rate might make it more easily tracked when it is being pursued. Movement at virtually any speed is an evenly paced gait with legs extended. When missing a leg or two it appears to favor this same gait, although (presumably when a leg has been injured) it may move and stand at rest with one leg slightly withdrawn. During travel it stops naturally and periodically when renewing its internal hydraulic blood pressure that, like most spiders, it requires to renew strength in its legs.
As suggested by its specific epithet reclusa (recluse), the brown recluse spider is rarely aggressive, and bites from the species are uncommon. In 2001, more than 2,000 brown recluse spiders were removed from a heavily infested home in Kansas, yet the four residents who had lived there for years were never harmed by the spiders, despite many encounters with them. The spider usually bites only when pressed against the skin, such as when tangled within clothes, towels, bedding, inside work gloves, etc. Many human victims report having been bitten after putting on clothes that had not been worn recently, or had been left for many days undisturbed on the floor. However, the fangs of the brown recluse are so tiny they are unable to penetrate most fabric.
The bite frequently is not felt initially and may not be immediately painful, but it can be serious. The brown recluse bears a potentially deadly hemotoxic venom. Most bites are minor with no necrosis. However, a small number of brown recluse bites do produce severe dermonecrotic lesions (i.e. necrosis); an even smaller number produce severe cutaneous (skin) or viscerocutaneous (systemic) symptoms. In one study of clinically diagnosed brown recluse bites, skin necrosis occurred 37% of the time, while systemic illness occurred 14% of the time. In these cases, the bites produced a range of symptoms common to many members of the Loxosceles genus known as loxoscelism, which may be cutaneous and viscerocutaneous. In very rare cases, bites can even cause hemolysis—the bursting of red blood cells.
Around 49% of brown recluse bites do not result in necrosis or systemic effects. When both types of loxoscelism do result, systemic effects may occur before necrosis, as the venom spreads throughout the body in minutes. Children, the elderly, and the debilitatingly ill may be more susceptible to systemic loxoscelism. The systemic symptoms most commonly experienced include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely, such bites can result in hemolysis, thrombocytopenia, disseminated intravascular coagulation, organ damage, and even death. Most fatalities are in children under the age of seven or those with a weak immune system.
While the majority of brown recluse spider bites do not result in any symptoms, cutaneous symptoms occur more frequently than systemic symptoms. In such instances, the bite forms a necrotizing ulcer that destroys soft tissue and may take months to heal, leaving deep scars. These bites usually become painful and itchy within 2 to 8 hours. Pain and other local effects worsen 12 to 36 hours after the bite, and the necrosis develops over the next few days. Over time, the wound may grow to as large as 25 cm (10 inches). The damaged tissue becomes gangrenous and eventually sloughs away.