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Thermonectus marmoratus

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Photo: Insectarium de Montréal, René Limoges

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Unlike most other members of their family, which are dull coloured, these shiny black diving beetles are covered in dozens of bright yellow dots. Their streamlined oval shape lets them swim easily, thanks to their paddle-like hind legs. The males and females are about 13 mm long.


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Aquatic habitats


Moving around

Country of origin

United States
French name
Scientific name
Thermonectus marmoratus
English name
Sunburst diving beetle
Living environment


In the wild, adults mainly hunt soft-bodied aquatic invertebrates. They seem to prefer mosquito larvae.

Their larvae are ferocious predators, consuming a wide variety of aquatic insects, including members of their own species.


They live in fresh water, mainly in ponds and streams, near deciduous forests.

Geographic distribution

They are found in the southwestern United States and adjacent regions of Mexico.

Ecological role

Diving beetles act as predators and carrion-eaters in the ecosystem.

Special behaviour

Diving beetles breathe at the surface thanks to orifices in their bodies. They can also carry a small supply of air with them when they dive, under their elytra – like a diver with a compressed air tank.

Unlike most Dytiscidae, this species tends to be gregarious; dozens of individuals may congregate in a small body of water.

Their bright colours serve as a warning to predators. When threatened, they give off an unpleasant substance. If a fish swallows one, it will spit it up again immediately and avoid these beetles in future.

Interesting facts


The species is very common in its range.

Interesting facts and curiosities

Diving beetles are agile, fast swimmers.

Like sharks, they use their sense of smell to track their prey.

The eyes of diving beetle larvae have two retinas, so that they are able to see clearly up close and at a distance.

When mating, the males grab onto the females’ backs using the suction disks on their front legs. They reproduce in the water.

At the Insectarium

In captivity they are fed crickets.

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