Face Value

What am I looking at?

This is a ventral view (that is, of the underside) of the head of a whirligig beetle (a member of the family Gyrinidae). These beetles are highly adapted to living at the interface of air and water; their four paddle-like legs make up one of the most efficient propulsion systems in nature. And to enable them to see both above and below the water’s surface, they evolved split compound eyes. In this image, you can see the beetle’s large ventral eyes (1), its mandibles (2), and its antennae (3) sticking out on either side of its head. The coloration is a combination of autofluorescence (colors generated when a laser shines on a sample) and of the red and blue fluorescence of Congo red and Calcofluor white dyes.

Click on the right arrow to see a dorsal (top) view of the beetle’s head and a view of its legs, which are highly adapted for swimming.

Biology in the background

Whirligig beetles, also called water beetles, got their name from the frantic circular patterns they make while swimming when they’re threatened. These beetles live almost exclusively in or on the surface of bodies of fresh water. As an adaptation to living at the interface of two elements, their compound eyes are split in two; effectively, these beetles have two pairs of eyes. One pair is located on the top of their head and can see above the surface of the water, while the other pair is located on the underside of their head and is submerged in the water. This gives them the ability to watch for predators both above and below the water and simultaneously to find prey underwater.

They can also trap a bubble of air beneath their elytra – the waxy, rigid, shell-like forewings covering the hindwings that they use for flight. This extra air supply allows them to dive and remain underwater for long periods of time.

Like many other water beetle species, male whirlygigs have forelegs with terminal segments (tarsi) that are adapted to attach to a female’s slippery elytra during mating. The mid and hind legs are paddle-like, with long setae – feather-like bristles – on their margins that fold when the leg is moved forward (to minimize drag) and expand when the leg is extended (to increase the surface area).

Whirligig beetles vary in size but can grow up to 14 millimeters long, or a little over half the size of a human thumbnail.  

Technique

These images were created using confocal microscopy and scanning electron microscopy.