Species Name: Great Diving Beetle - Dytiscus marginalis

How to recognise

The great diving beetle adult reaches over 30mms long. The male has smooth wing cases and large sucker pads on its front legs that are clearly visible. The female has ridged wing cases that are duller and no sucker pads and is slightly smaller than the male with the front four legs hairless.

Diving beetles often look black but on close examination have an attractive green sheen on their backs with a yellow border round the outside of the wing cases and behind the head. Some female beetles appear brown or reddish-brown.

The larvae grow up to 5cms in size and are voracious predators with large heads and powerful jaws. The larvae swims in an ‘S’ shape in deep waters with its abdomen at the surface and its head pointing forward. 

Where to see

Well vegetated ponds, and dykes with abundant water plants. This species, and the related silver diving beetle, are found in the Norfolk Broads. Great diving beetles are  thought to be widespread across Norfolk. The adults fly well and can turn up in surprising places including swimming pools and children’s paddling ponds!

When to see

Larvae and adults are most often seen in spring and summer. Both stages may be present in water bodies throughout the year, though are less active in cold temperatures.

Conservation status in Norfolk

Widespread and common. Not threatened.

How to help

Great diving beetles are often found in garden ponds. By creating a garden pond you will benefit a wide range of aquatic invertebrates including the great diving beetle.

Did you know?

The adult great diving beetle stores air beneath its wing cases to allow it to stay underwater for longer to hunt.

The larvae and adult great diving beetle are carnivorous. The larvae feed on other insects, tadpoles and even small fish, catching prey in their large jaws then injecting enzymes into the body. These enzymes dissolve the victim’s internal organs which are then sucked into the diving beetle’s mouth.

During the evening and night adult diving beetles sometimes leave the water and can fly long distances colonising new ponds.

Finding out more

Buglife

Go back