From how far can flies smell food?

21 February 2013

Question

Apparently flies can smell meat from 7 kms away. Is it true? And if so how? And I would appreciate knowing how it could be determined that flies could smell meat from specifically 7 kms away. Please help.
Thank you. Desiraee De Verneuil

Answer

Marcus - Hi. I'm Marcus Stensmyr from the Max Planck Institute for Chemical Ecology in Germany. Yes, it's true. A fly could smell meat over that distance although only under very, very favourable conditions. Mark-release-recapture experiments performed with house flies caught at the poultry farm showed that flies could find their way back to the farm from a distance of up to 7 km. To get this data, the scientists had to tag and release 160,000 flies which only 0.05% were recaptured. So, flies can do it but far from all will manage this feat. 7 km is not only a considerable distance to smell something. For a tiny fly, simply traveling 7 km is a major effort, taking several days. Even so, flies are able to detect a smell of rotting meat over long distances. The exact distance depends on many factors such wind conditions, size of the meat and landscape features.

For flies to smell something 7 km away, it nevertheless has to be a substantial piece of meat like a herd of dead elephants rotting away in the sun or an entire poultry farm. How do flies manage this? Well, it involves no magic - simply, a very good sense of smell. Flies like all other insects detect odours with their antennae which are densely colour in hair-like structures containing olfactory sensory nerve cells. These nerve cells are extremely sensitive to volatile chemicals, odours that is. And in the case of flies that feed on the dead and decaying flesh, so-called Carrion flies, their olfactory cells are also optimised towards detecting cadaver odours.

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