Foot of the Diver

What am I looking at?

These images show the underside of the front foot of a male diving beetle. You can see suction cups (1) that are used during mating, as well as a broad plate (2) and exterior spines (3) that aid in swimming. The colors you see are the result of a combination of autofluorescence (colors generated when a laser shines on a sample, which is a key step in confocal microscopy), as well as red and blue-green stains that bind chitin, the main component of an insect’s exoskeleton.

Click on the right arrow to see another angle of this insect’s foot.

Biology in the background

These beetles can be found all over the world and live in a wide variety of freshwater environments. The front foot of a male diving beetle evolved as a means of attaching to the back of a female during and after mating. Female diving beetles don’t like giving piggyback rides to males because the males typically try to mate with multiple partners. Attached males also steal some of the food females catch, slow them down, and make it harder for the females to reach the surface for air.

For these reasons, females evolved structures on their backs that make it more difficult for the males to stay attached. In turn, this drove further adaptation of males’ front feet, resulting in several sets of suction cups of various sizes that make it easier for them to stay on a female’s back as long as possible.

The front foot of a diving beetle is about 2 millimeters across, or roughly 25 times the width of a human hair. Its hind leg is about 1.5 millimeters long, or roughly 20 times the width of a human hair.

Technique

These images were captured using confocal microscopy.