A new study details the evolution of spider and centipede venom. Researchers say the poison that today proves fatal for so many small insects, was once a harmless hormone.

Australia's funnel web spiders species use neurotoxins to paralyze their prey. The toxins occasionally proved fatal to humans prior to the 1981 introduction of effective antivenom.

Several thousands years ago, scientists say, the fast-acting poison's antecedent was a hormone used to regulate sugar metabolism, functioning much like the human body's insulin.

Researchers weren't able to recognize the derivation by comparing genetic sequences. The modern venom's complex molecular makeup -- some contain nearly 3,000 peptides -- are too far evolved to resemble the ancient hormone.

But scientists noticed the similarities when comparing the molecular structures of insulin-like hormones and venom.

"If you take the sequence of the spider toxin and you do a BLAST search, the hormone is so different now that you don't pull it out," study senior author Glenn King, a biochemist and structural biologist at the University of Queensland's Institute for Molecular Bioscience, said in a press release. "But when we did a structural search and it pulled up the hormone, that's what really surprised us -- the sequence didn't tell us where the toxins evolved from, but the structure did pretty clearly."

A BLAST (Basic Local Alignment Search Tool) search is analysis technique that looks for regions of local similarity between different genetic sequences.

Now that researchers have a better understanding of venom's structure, they hope to manipulate its sequencing to create new drugs or other beneficial substances. Of the venoms studied, researchers found centipede poison to have evolved to be the most stable -- and thus the most ripe for manipulation in the lab.

The revelation is exciting, but scientists aren't sure exactly how the hormone became venom. It may be that what began as a biological experiment, slowly evolved into a permanent adaptation.

"If a hormone does something bad to prey, you might recruit it into the venom and make lots of it," King said. "That's the starting point and it can then evolve to become more potent."

The new research was a collaborative effort among scientists from Australia's Queensland University and Lewis & Clark College in Portland, Oregon. The study was published in the journal Structure.