Dytiscus are large water beetles with a robust, rounded shape and they measure 2.2–4.4 cm (0.9–1.7 in) long depending on the exact species involved.

The larvae (known as "water tigers") are elongate with a round and flat head and strong mandibles.

Once the larvae grow to some size, they move to soil at the edge of water and burrow into a cell and pupate.

In Dytiscus marginalis and other species the tarsus of the forelegs is modified in males to form a circular sucker.

[2] Eggs of Dytiscus are sometimes parasitized by wasps of the families Eulophidae, Mymaridae and other Chalcidoidea.