The diving beetles (Dytiscidae) are a speciose family comprising more than 4000 species worldwide. 150 species are known to occur in Germany. Most species are of oval shape and their body length varies considerably, e.g. Hydroporus scalesianus is only 2 mm long, whereas Cybister lateralimarginalis is one of our largest species with close to 40 mm body length. They are good swimmers and can be found in different types of waters rich in plants, e.g. ponds, lakes, brooks, even in brackish water. They are predators of other insects, tadpoles and fry. Many of them are able to fly and can easily colonize new habitats. Many species exhibit a marked sexual dimorphism: males have suction pads on their front legs, females may show rippled elytra while the elytra of the male are plain.