Receiving a spider bite is rarely a pleasant experience. Some spider bites leave little to no signs a bite even happened, while others can have truly nasty effects on the surrounding tissue. What happens to your skin after a spider bite? What causes the damage to your skin? This brief guide to the pathophysiology of spider bites will tell you more about why and how spider bites affect you.
Most Spiders Are Not Dangerous
Not all spiders harm you with their bites. In fact, most spiders do not have mouth parts large enough to pierce human skin. Unfortunately, some spiders do. Any time the skin is pierced, infection may set in if the wound is not properly cared for. Even with proper wound care, further injury from a spider bite is still possible, and usually occurs due to the venom spiders inject into the area.
Spider Venoms
While most spiders’ venom is not toxic to humans in the amounts injected, some venoms can cause injury severe enough to require medical attention. However, most spider bites are not fatal. In general, spider venoms act in one of two ways:
- Neurotoxic. Neurotoxic venoms are the venoms spiders use to paralyze their prey. When injected into a large mammal such as a human, neurotoxic venoms work to excite the nervous system. Venoms affecting the motor nerves can cause muscle spasms, cramps, and twitching. Venoms affecting the autonomic nerves can cause goose bumps, sweating, drooling, and increase heart rate and blood pressure.
Spiders with neurotoxic venom include widows, Australian funnel web spiders, and Brazilian wandering spiders.
- Necrotic. Necrotic venoms cause tissue death in order to kill their prey. When injected into human skin, there may be no ill effects at first. Within two to eight hours, the bite becomes painful and itchy, worsening over the next 12 to 36 hours. Necrosis sets in over the next few days and may transform the red, swollen bite into a dry, black ulcer. The damaged tissue may develop gangrene and fall away, healing only after months or even years.
Spiders with necrotic venoms include members of the Sicariidae family, including recluses and six eyed sand spiders.