(including Dytiscus harrissi, Dytiscus marginalis, Dytiscus fasciventris, and Dytiscus verticalis)
There are several species of Large Diving Beetles, but they are difficult to tell apart. They all grow between one and 1 1/2 inches long. They are dark brown or black with a greenish tinge. They have yellow along their sides and on the bottom. Females have many grooves on the back wings. The legs of these beetles are yellow or brownish.
Large Diving Beetles live in ponds, streams, or rivers. They do not like large lakes, unless there is a shallow, quiet section.
Large Diving Beetles should not be confused with Small Diving Beetles, which are much smaller. Small Diving Beetles never grow more than half an inch.
These beetles spend most of their lives under water. They swim with strong back legs that they use like oars on a rowboat.
Sometimes they leave the water to fly to another pond.
The larvae of Large Diving Beetles are called water tigers, because they are vicious predators that attack any creature smaller than them, and many which are larger than them. Some of the foods water tigers eat include small fish, frogs, toads, salamanders, tadpoles, and larvae of other insects.
Adult Large Diving Beetles are also predators, eating many of the same foods as the larvae, plus insects that get trapped in the surface film (sticky layer on the surface of a pond).
Both the larvae and the adult beetles must breathe air. The adults have tiny holes on the sides of their abdomens (back body section) which they can breathe air through. These holes are called spiracles. They also have strong outer wings, called elytra. When a beetle swims to the surface, it sticks its abdomen out into the air. The beeetle traps an air bubble between its elytra and its abdomen. It can then dive underwater, carrying its air bubble with it. The beetle breathes from the air bubble through its spiracles. This way it doesn't have to go up for air very often.
Water tigers are light-weight and will float if they don't hold onto the bottom or plants. To breathe, they climb up a plant or just let go and float to the surface.
After mating, female Large Diving Beetles lay eggs one at a time by injecting them into an underwater plant stem. They use a needle-shaped object that sticks out of their abdomen, called an ovipositor. You've seen an ovipositor if you've looked closely at a female cricket. They have them too.
The eggs hatch into larvae (water tigers). When the water tigers are fully grown, they will crawl out of the water onto the shore. They will then begin to breathe air immediately through their spiracles. The water tigers look for a place to turn into pupae (resting stage). Usually, they crawl under a stone, old log, or some leaves near the shore.
A pupa is a lot like a coccoon. It is a resting stage, where the larvae will transform into an adult beetle. Once the larva has turned into a pupa, it will be a few weeks before it comes out as an adult. Many pupae drown because they breathe air (even while they're resting) and they cannot get up and move if heavy rains flood the pond or stream and raise the water level.
Once the adult diving beetle emerges, it will immediately return to the water. They can live three years or more. During Winter, they hibernate by burrowing into the bottom. Even though they breathe air, they can survive by slowing down their bodies into a deep rest that doesn't need much oxygen. When warm weather arrives, they swim back to the surface for a fresh gulp of air.
Predators of Large Diving Beetles include fish, frogs, and ducks. Water tigers are also sometimes eaten by other large aquatic insects, such as dragonfly nymphs.
Relationships in Nature:
Relationship to Humans:
Large Diving Beetles help control populations of insects and other animals. Sometimes they are attracted to porch lights when they are flying around. If handled they will bite, but they don't do any real damage.