In labs around the world, scientists study malaria by injecting rodents with Plasmodium—the parasites that cause the disease. These experiments are necessary but also artificial. In the wild, the needle that spreads malaria isn’t a hypodermic syringe, but a mosquito’s snout.

Both delivery routes end in infection, but they have very different effects. Philip Spence from the National Institute for Medical Research in London has found that malarial parasites cause less severe disease if they have spent time in a mosquito—that is, they become less virulent. Something in them changes so that when they move into a mammal, they trigger a stronger immune response, grow less well and cause milder symptoms.

A word of caution: This doesn’t mean that mosquitoes are protecting