Predaceous Diving Beetles

By Anonymous -
By Regina Davis, Taylor Marshall, & Ali Bland

Predaceous diving beetles are from the family Dytiscidae, which is from the Greek root word dytikos, meaning “able to dive.” Adult beetles are usually dark brown, black, or tan with gold highlights. The presence of distinct body markings can indicate specific subfamilies. The diving beetle, like many other members of the order Coleoptera have a head, thorax and abdomen with six legs. The predaceous diving beetle has two pairs of compound eyes, one pair above the water line, and one pair below. This adaptation, used to avoid predators and track for pray, allows the beetle to see both above and below the water line when it is floating on the water’s surface. The predaceous diving beetle has hind legs that are flat, broad, and are covered in hair-like filaments to allow for easy locomotion through water and also add to the leg’s surface area making it easier to float in the water.


The beetle’s “frog-like” swimming movement involves simultaneously kicking out their back legs to propel themselves through the water. Some male species of predaceous diving beetles have suction-like cups on their front legs. This allows them to stay connected to a female while mating. The smooth, streamlined body of the predaceous diving beetle also allows for less friction and higher speeds in the water. Their spiracles (which allows oxygen exchange) are located under the elytra. These are the hardened plates of chitin over their wings. The beetles trap air under their elytra before they submerge in water. Their spiracles are then able to exchange oxygen while they are diving and allows them to stay underwater for longer periods of time. When the beetles’ water source dries out they use their strong wings to fly to another water source. Larvae are long and flattened with strong pincers used to grab prey.


The predaceous diving beetle is an aquatic insect, as indicated by its common name. Adults and larvae can be found in slow moving streams, ponds, marshes, smaller lakes, and pools. They are found all over the world where slow moving water is present, typically along the edges of the water floating among the plants. Predaceous diving beetles use their tactical aggressive behavior to violently assault not only small insects, insect larvae, tadpoles, but also full-grown bullfrogs. The predaceous diving beetle also finds itself as prey to several different species of fish, birds, and other small mammals.
The life cycle duration of this family of beetles can vary within species, but in general the predacious diving beetle has a larval and adult stage. Eggs are usually laid on submerged vegetation, and when hatched the larval stage of the beetle emerges. Their larval stage is commonly known as a water tiger. The larva can grow up to 2 in long, and have the same pinchers for feeding that the adults exhibit.  However, the larvae use their needle-like jaws to inject poison into their prey, which then dissolves the body tissues for them to eat. Water tigers are known to be more aggressive than the adults but are carnivorous as are like the adults’. They feed on the larval stages of other aquatic insects such as dragonfly larvae, and occasionally small “fry`s” (baby fish). It is also not uncommon to see them cannibalize each other.


Predaceous diving beetles are a major part in the food web of streams and lakes. One major threat to their existence is human pollution of these bodies of water. Without these intriguing beetles, the balance of the ecosystem they are from can be greatly disturbed. Humans can sometimes find them to disadvantageous because they eat fish and compete with them for resources, taking out a major food source which they cannot replace.

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