Recluse Spider - Venom Components and Effects

Venom Components and Effects

Loxosceles spiders, like their cousins in Sicarius, have potent tissue-destroying venoms containing the dermonecrotic agent, sphingomyelinase D, which is otherwise found only in a few pathogenic bacteria. Recent research has indicated the venom is composed largely of sulfated nucleosides, though these compounds are relatively new discoveries, so little is known about them. This venom is highly necrotic in effect, capable of causing lesions (open sores) as large as a bottle cap. The wounds take a long time to heal and may require skin grafts. If these open wounds become infected there are often serious consequences. Rarely, the venom is carried by the blood stream to internal organs causing systemic effects.

The constituency of recluse venom is identical in both male and female spiders, although females have a particularly potent venom, containing up to twice the concentration of toxins. For unknown reasons, the toxicity of the venom to mammalian species varies—recluse bites will cause necrosis in humans, rabbits, and guinea pigs, but not in mice or rats.

The Chilean recluse (Loxosceles laeta) supposedly has a more potent venom, which results in systemic involvement more often. This spider was accidentally introduced to the Los Angeles area (Alhambra, Sierra Madre, and Monterey Park). This spider, however, seems to be confined to a very limited area, even though it has lived there for over 30 years. Other members of the genus that have been tested have venoms similar to the brown recluse and all members of this genus are best avoided. However, the brown recluse and its relatives are not very aggressive and huge populations have been found in houses where the human inhabitants remained unbitten after years of cohabitation.

A possible problem with diagnosing a recluse spider bite is that the bite of these spiders is probably both underreported in some areas and overreported generally. Unfortunately several diseases can mimic the lesions of a recluse spider bite, including Lyme disease, various fungal and bacterial infections and the first sore of syphilis. Therefore it is extremely important to associate the spider directly with the bite, if at all possible, and consider alternative diagnoses if no spider was seen.

Recluse spiders are usually found in the center of space webs made of fungus-like silk, which often contains the remains of their recent meals. The most abundant food items for the Arizona recluse (Loxosceles arizonica) are night-active ants such as carpenter ants. The brown recluse feeds on whatever small prey is available. This is also true of all sicariids. Loxosceles reclusa have been shown in laboratory experiments to prefer scavenging than actively hunting.

Bites most often occur when the spider is engaging in defense while trapped against the skin, such as when the person is putting on clothes the recluse is inside of, or when the person while sleeping rolls over against the recluse. However, bug spray and other chemicals intended to repel or kill arthropods that do not kill the recluse will cause its nervous system to break down partially, inducing undesirable aggressive behavior.

The bite of a recluse spider can generally be categorized into one of the following groups:

• Unremarkable - self-healing minute damage
• Mild reaction - self-healing damage that displays itchiness, redness, and mild lesion. Most bites fall into the unremarkable or mild reaction categories.
• Dermonecrotic - (uncommon) necrotic skin lesion (the "classic" recluse bite). Approximately 66% of necrotic lesions caused by this type of bite heal with no complications. In extreme cases, the lesion may expand to as many as 40 cm in width, last for several months, and cause a permanent scar.
• Systemic or viscerocutaneous - (extremely rare) a fatal blood system condition. The occurrence of this type of bite is directly related to obesity of the victim (as the venom destroys adipose tissue), and it is life-threatening, particularly to children.