Spider venom reveals new secret.

• Position: Poisoning

The genus Loxosceles, which contains about 100 spider species, includes the brown recluse (or fiddler spider), whose venom, it turns out, produces a different chemical product in the human body than scientists believed. The finding has implications for understanding how these spider bites affect humans and for the development of possible treatments.

One of few common spiders whose bites can have a seriously harmful effect on humans, the brown recluse has venom that contains a rare protein that can cause a blackened lesion at the site of a bite, or a much less common, but more dangerous, systemic reaction in humans. "This is not a protein that is usually found in the venom of poisonous animals," points out chemist Matthew Cordes, who led the study, published in the journal PLOS ONE.

The research team discovered that the venom protein causes lipids to bend into a ring structure, generating a cyclical chemical product that is very different than the linear molecule it was assumed to produce. "The very first step of this whole process that leads to skin and tissue damage or systemic effects is not what we all thought it was," Cordes notes.

The lipid knocks off its own head by making a ring within itself, prompted by the protein from the spider venom. The cyclical shape of the headless molecule means that it has different chemical properties than the linear headless lipid previously believed to be generated by the protein.

For those who do have a reaction to the venom, the most common response is inflammation that, after one to two days, can develop into a dark lesion surrounding the bite site. The blackening, or necrosis, of the skin is dead skin cells, evidence of the immune system's efforts to prevent spread of the toxin by stopping blood flow to the affected area.

"Our bodies are basically committing tissue suicide," explains biologist Greta Binford, a member of the research team...