Scientists have discovered how migrating locusts avoid the danger of flying over the sea.
The locust: A pest all over the world
Experiments show the insect is capable of detecting the polarised reflections of large bodies of water.
This means it can switch flight paths when it encounters water, boosting its chances of survival.
The research could lead to novel deterrents for locusts, which can devastate large areas of farmland.
Many animals have eyes that are sensitive to polarised light: basically light reflected off a flat surface.
Light reflected from the sea is partly linearly polarised and this may provide a flying insect with an indication of the nature of the surface below them. Insects that live on or near water, for example, are attracted to such surfaces.
Now, scientists in Israel and the US have confirmed that the eye of the locust is sensitive to polarised light and that it uses this ability to avoid crossing water.
They found that tethered locusts avoided flying over a light-reflecting mirror and, when given the choice, preferred to fly over a non-polarised reflecting surface rather than reflected linearly polarised light.
The locusts are attracted to new growth
This may help migrating locusts avoid flying over water in coastal areas, particularly at low altitude, according to Dr Nadav Shashar, of the University of Maryland Baltimore County, and colleagues.
"For a migrating desert insect, water presents a potential hazard and large bodies of water, such as the sea, are especially dangerous," they write in the journal Biology Letters, published by the Royal Society.
"Therefore, detecting and avoiding such surfaces is beneficial to them."
The idea for the study came from observations by volunteers of an outbreak of locust migration near the Gulf of Aqaba last November.
Swarms crossed the length of the Sahara desert to reach Egypt via the Sinai desert. But instead of crossing the 3-5km-wide Gulf, they turned north and flew over land, turning back towards the shore if they veered over water.