"The Amazing Spider-Man," which retells the origins of Marvel's wall-crawling superhero, hits theaters Tuesday. In the comic, a bite from a radioactive spider gives Peter Parker strength, agility and -- in some versions of the story -- the ability to shoot webbing out of his wrist. What really happens to someone bitten by a radioactive spider?
Not much. Or rather, not much aside from the usual symptoms of being fanged by an arachnid: itching, redness, soreness, and sometimes -- depending on the type of spider -- more serious symptoms, including unconsciousness or death. The radioactivity, though, would be irrelevant. The world is awash in radiation. We're exposed to about 3 millisieverts of it a year, mostly from the sun and naturally occurring radioactive gases like radon. That's not counting doses from medical procedures such as CT scans (6 mSv), mammograms (.4 mSv), or X-rays (.1 mSv); from airline travel (.01 mSv); or from smoking (53 mSv per year). The amount of radiation contained in the venom from a single spider bite would likely fall between .00003 and .000003 mSv -- an inconsequential dose, about as much radiation as you'd absorb from eating a banana, which contains the radioactive isotope Potassium-40.
Radioactive creatures do exist, notably in the forests surrounding the damaged Chernobyl nuclear reactor in the Ukraine, as well as in Sweden and Finland, where plumes of radiation fell after the 1986 disaster. (Being irradiated, or exposed to radiation, is not the same as being radioactive, which means that your body contains radioactive matter.) But even a large radioactive creature, such as a wolf or bear, wouldn't have enough radioactivity in its venom or saliva to pose a health risk (although the bite itself could still be deadly).
Even more common than radioactive animals are radioactive plants, which absorb nuclear fallout from the air or polluted groundwater. Though an insect bite won't give you radiation poisoning, consuming too many compromised flora and fauna will. In Belarus and the Ukraine, contaminated cows and steers eat "clean" hay until the concentration of hazardous isotopes in their bodies dips below the safety threshold. And a population of Swedish roe deer recently alarmed hunters when they showed above-average levels of radiation after feeding on especially radiation-concentrating mushrooms.
Radioactive animals exhibit a higher than usual rate of birth abnormalities; birds near Chernobyl have been shown to have smaller brains, and insects there are frequently born discolored. Still, even the most potent radioactive isotopes (unstable forms of strontium, plutonium, cesium, and iodine) are not capable of causing Marvel-grade mutations, as radiation proves far better at killing cells than at transfiguring them in some useful way.
Reports of people being bitten by radioactive animals are few and far-between. Several years back, however, a man working to clean up the Chernobyl grounds was attacked by a radioactive stray dog. He was immediately hospitalized -- for rabies.