Bug FAQCosmopolitan Diving Beetle
Rhantus suturalis · Order: Coleoptera · Family: Dytiscidae
The cosmopolitan diving beetle is a small aquatic predator about 10.5 to 13 mm long, with a black head, pale markings, a pale pronotum with a central dark spot, pale brown elytra, and completely black abdominal sternites. Adults and larvae hunt mosquito larvae, midge larvae and water fleas, and they are present all year, overwintering in the water.
Source: Wikipedia
How to recognize it
The pronotum is pale with a usually clear dark mark in the middle. The wing covers are pale brown and have fine punctures. The underside plates of the abdomen are entirely black.
Source: Wikipedia
Size
Adults measure between 10.5 and 13.0 mm in length.
Source: Wikipedia
What it eats
Both adults and larvae are predators that mainly eat mosquito larvae. They also feed on midge larvae and water fleas.
Source: Wikipedia
Life cycle
Breeding takes place in spring and early summer, with eggs laid among submerged debris. The larval stage lasts about three weeks and includes three instars.
Source: Wikipedia
When you see it
Adults can be found throughout the year. They are thought to overwinter in the water.
Source: Wikipedia
Where it comes from
The species has a cosmopolitan distribution, occurring worldwide.
Source: Wikipedia
Lookalikes
In Europe it can be confused with R. exsoletus, which has a vague black rear edge on the pronotum and yellow abdominal sternites instead of black.
Source: Wikipedia
More photos
Questions people ask
What do they eat?
They prey on mosquito larvae, as well as midge larvae and water fleas.
Source: Wikipedia
Same family (Dytiscidae)
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Sources
- Wikipedia: https://en.wikipedia.org/wiki/Rhantus_suturalis
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.