Foreleg of a male diving beetle

Spike Walker

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Polarised photomicrograph showing the rows of suckers on the foreleg of a male Dytiscus marginalis. Commonly known as the great diving beetle, these are largest freshwater beetles in the UK. They have a large streamlined body that is dark brown in colour, with a yellow abdomen and yellow legs. This image was produced by passing light through coloured filters, a technique known as Rheinberg illumination.

What are the suckers for?

Male beetles are distinguished from females by the presence of suckers on their front legs. The great diving beetle spends the majority of its time underwater hunting for food, such as other insects, tadpoles and small fish. They also mate underwater, and to aid this, the males have developed plate-like proximal tarsal joints on their front legs that are covered in suckers, allowing the male to hold onto the female during mating. The image shows a portion of such a joint, showing part of one of the two larger suckers and five rows of small ones.

Why did the judges pick this image?

Fergus Walsh, Wellcome Image Awards judge and BBC medical correspondent, comments: "Like many of the images, this would not be out of place in an art gallery. It reveals the beauty and biology of nature in exquisite close-up detail. I can't imagine having a picture of a great diving beetle on my wall, but this I could."

Eric Hilaire, Picture Editor at the 'Guardian', agrees: "The first time I saw a print of this photomicrograph, I, for a second, wanted to look for a signature as if it was a painting. Later I tried to work out what it was that made me react this way. Obviously, the first reason is the artistic skills of well-known photomicrographer Spike Walker: the subtle framing as well as an evocative choice of colours that recalls the brightness of dry pastel. Then, it was also the way I was reading this picture: a large red sun spreading its rays toward rows of shooting plants, maybe in a garden bed? Looking at it again today, I appreciate even more this image that draws, for me, a similarity between photomicrography and rubbing: revealing hidden shapes."