Sweetgrass reveals its repellent secrets

Chemists have identified the two key chemicals in sweetgrass, a plant that Native Americans traditionally used to fend off insects.

They distilled compounds from the grass in the lab and tested which ones could keep mosquitoes away from tantalising fake blood samples.

Two compounds in particular, coumarin and phytol, worked just as effectively as the widely-used repellent Deet.

Here, lead researcher Dr Charles Cantrell, from the US Department of Agriculture, describes the indigenous customs that got his team interested in the grass - as well as some of the experiments.

He was speaking at the 2015 Fall Meeting of the American Chemical Society, in Boston.