Part of the show Plant Science, Composting and Mosquito Repellents
Matt in Melbourne asked:
For the last week there have been flies at work and they're more annoying than ever. By this I mean that they continually fly around your face, even when you've physically hit at them. I was wondering if there was any kind of smell or attractant that the human emits that attracts these flies, or is it something to do with moisture?
Many flies, which includes the mosquito and the biting midge, use carbon dioxide, heat and various other chemicals that are quite commonly produced. But they will also use specific compounds to see human beings. For example, the malaria mosquito can find a human being in the middle of a very large group of cows, which are oozing carbon dioxide and heat. It uses specific chemicals to find that human subject. It will be the same for the flies that are annoying the friend in Melbourne. These insects are able to perceive what kind of potential host they've got, even if it's not blood they're after, just the mucus around our eyes and mouths.