

The Venom Chronicles: Super Spiders

There are more than 41,000 described species of spider, and over 99% of them are venomous. Mercifully, there are only four small groups of spiders whose venom is lethal to humans, but insects beware: Spider venom can inflict a cocktail of unpleasant symptoms, from full-body convulsions and paralysis to spontaneous cell death that dissolves your body while you're still conscious. With so many species and so much time to diversify, spiders have developed methods to capture and kill just about every kind of insect prey out there. And now, humans are developing ways to take advantage of diverse spider toxins to create pesticides that kill insects without harming humans or the environment.

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Image Courtesy Bruno Santos
Greta Binford spends most of her time doing research at Lewis and Clark College in Oregon, but when she's not in the lab, she can be found hunting down the deadly brown recluse spider everywhere from peculiar haunts like the basement of a Goodwill store in Los Angeles to the mountains in their native Peru. They are generalists that will eat pretty much anything that walks by, but other spiders are much more specialized. Tarantulas live in holes and only capture things that come near their dwellings; orb weavers catch insects in flight. A few species spit toxic glue at their prey; others dash underwater and bite fish. Most interesting of all to researchers like Binford is that all these spiders' venoms reflect the diversity in how and what they catch.
Studying spider venom is an arduous task. There are two basic strategies: either examine the genes a spider expresses in the venom gland, or try and break down the venom itself. In the first case, Binford electrically stimulates a spider, waits 24 hours, and then pulls out the tiny fragments of genetic material floating around in the venom gland tissue. She can then use the fragments to piece together the whole genetic code for the venom. The second approach involves slowly and meticulously separating the components in a sample of venom and identifying each ingredient by matching its molecular weight against a database of known spider toxins. Though it sounds easier, this method has its own problems. There is no good database already in existence, and with as many as 4,000 components in a single spider's venom, it can take a large sample and huge amount of time to parse them all out.

Binford uses the data she collects from venom to piece together the evolutionary history of spider species. But why bother? Binford explains that the most powerful tool we have in understanding venom is the evolutionary tree itself. There are over 41,000 spiders species alone, and perhaps hundreds of thousands of other venomous animals, so our current picture of how all the venomous species are related is fairly spotty. But a more complete understanding of how and where venom evolved would help explain how certain toxins ended up in certain places along the evolutionary tree. This could enable scientists to more easily decipher what's in the venom samples they already have, and to make predictions about what kinds of toxins we'll find in newly discovered species. Evolution turns out to be a great structural framework for understanding venom chemistry.

And understanding venom chemistry is beginning to have some exciting new applications. Glenn King, a professor at the University of Queensland in Australia, is developing ways to use components of spider venom as targeted pesticides. From an evolutionary perspective, this makes perfect sense. Spider venom has evolved specifically to target insects, so if we can isolate the toxic proteins that kill insects without harming humans, we'd have some very effective and completely biodegradable pesticides.

To figure out which proteins accomplish that goal, King tests possible toxins on newborn mice, mammals that are especially sensitive to neurotoxins. None of the toxins being developed are at all harmful to the newborn mice, even at very high doses. King acknowledges that a lot of people might be hesitant to spray their plants with spider toxins, but says this is a problem of perception rather than reality. Only a microscopic percentage of spider toxins are harmful to humans anyway, and tests like the ones on baby mice weed those out long before they come in contact with our food.

Evolution and natural selection may have created chemicals that do their jobs better than the synthetic ones humans create. We have nature--and the spiders themselves, of course--to thank for these incredible toxins. And as scientists continue fill in the gaps in the spider's evolutionary tree, they are bound to discover even more ways to take advantage of their unique adaptations.

This is the third installment of The Venom Chronicles, a blog series by Hannah Krakauer, a research intern at NOVA and a student at Stanford University. From more on the science of venom, watch Venom: Nature's Killer streaming online, or check your local listings to find out when it will air near you. 

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