CAN DRAG­ON­FLIES SEE IN THE RAIN?

iD magazine - - Nature -

It can hover in place in midair, fly back­ward, change di­rec­tion in frac­tions of a sec­ond, and pa­trol your gar­den at 40 miles per hour. A drag­on­fly’s com­pound eyes, which are made up of 30,000 in­di­vid­ual units that con­tain pho­tore­cep­tors, can spot prey at a dis­tance of 130 feet. These eyes are po­si­tioned on each side of the in­sect’s head to af­ford it a 360- de­gree field of vi­sion. Drag­on­flies also see more col­ors than hu­mans. But as soon as that first rain­drop hits the ground, all this high-tech equip­ment no longer does it any good.

Now its po­ten­tial prey can take a short break. The wa­ter droplets that have cov­ered a large part of its mul­ti­fac­eted eyes cause a to­tal fail­ure of the op­ti­cal sys­tem. The land­scape around the drag­on­fly be­comes blurred, the oth­er­wise highly pre­cise flight paths be­come mud­dled. The chance of de­tec­tion by an en­emy is high. At this mo­ment the hot­shot avi­a­tor is out of com­mis­sion. But the drag­on­fly wouldn’t be a drag­on­fly if na­ture hadn’t pro­vided some so­lu­tion to the prob­lem. On the in­side of each of its front legs is a row of spiny acan­thae used for wip­ing dirt or wa­ter from the eyes dur­ing flight. The legs are usu­ally kept tucked away be­hind its head like wind­shield wipers and are only folded out when needed.

Un­like adult drag­on­flies, their young, called nymphs, are right at home in the midst of wa­ter. In fact they are aquatic for up to the first two years of their lives. Dur­ing this time be­fore they ma­ture and be­gin liv­ing on land and in the air, they breathe via gills in their rec­tal cham­ber.

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