Dytiscidae

The Dytiscidae – based on the Greek dytikos (δυτικός), "able to dive" – are the predaceous diving beetles, a family of water beetles. They are about 25 mm (1.0 in) long on average, though much variation is seen between species. Dytiscus latissimus, the largest, can grow to 45 mm long. Most are dark brown, blackish, or dark olive in color with golden highlights in some subfamilies. They have short, but sharp mandibles. Immediately upon biting, they deliver digestive enzymes. The larvae are commonly known as water tigers. The family has not been comprehensively cataloged since 1920, but is estimated to include about 4,000 species in over 160 genera.

Larvae and development

When still in larval form, the beetles vary in size from about 1 to 5 cm (0.5 to 2.0 in). The larval bodies are shaped like crescents, with the tail long and covered with thin hairs. Six legs protrude from along the thorax, which also sports the same thin hairs. The head is flat and square, with a pair of long, large pincers. When hunting, they cling to grasses or pieces of wood along the bottom, and hold perfectly still until prey passes by, then they lunge, trapping their soon-to-be-food between their front legs and biting down with their pincers. Their usual prey includes tadpoles and glassworms, among other smaller water-dwelling creatures.