Venom Potensy Varies from Snake to Snake.

• Position: RATTLESNAKES

In a surprising evolutionary twist, a study in the journal Biology Letters suggests that, while one rattlesnake may routinely feast on lizard meat, its seemingly identical neighbor snake might strike repeatedly and yet never kill its would-be reptilian prey.

The research reveals significant venom variation within populations of Florida pygmy rattlesnakes, showing that effectiveness against one type of prey differs widely among individuals and opening up questions about why this variation exists.

Scientists long have understood that these types of differences existed between different populations of snakes of the same species, and that made good intuitive sense, because they were living in different environments, with different dietary options at the ready, but to find widespread variability between individual members of a group of snakes born and bred in the same area is perplexing.

"We found differences within the same population that were almost four times greater than differences in toxicity between snakes from different regions," says senior author and evolutionary biologist H. Lisle Gibbs. "To my knowledge, nobody has ever documented anything like this before--we've all been focused on...