#diving beetle

Great Diving Beetle (Dytiscus marginalis), male, family Dytiscidae, Czeck Republic

You have subscribed to DAILY BUG FACTS

🪲

TODAY'S FACT IS

Did you know that Limbodessus Bennetti is a species of subterranean diving beetle? These carnivores measure a gigantic 1.65mm in length and are relatively flat to help with their aquatic activities. This species is only known to be found in a single aquifer in northern Pilbara, of Western Australia.

🪲

Thank you for subscribing to DAILY BUG FACTS

Welcome to Wet Beast Wednesday, where this week, I am once again discussing God's favorite (or perhaps most feared) animal: the beetle. Beetles are the most diverse and among the most successful of all insects, so it shouldn't come as a surprise that they've adapted to aquatic lifestyles.

(Image: a predaceous diving beetle underwater. It is a green beetle with yellow outlines and large eyes. The front 2 pairs of legs are short while the rear pair are large and hairy. End ID)

The predaceous diving beetles are over 4,000 known species of beetle in the family Dytiscidae. They are oval-shaped, with flattened bodies and elytra (wing cases) that cover most of the upper body. The body is smooth and streamlined to make it hydrodynamic. Predaceous diving beetles have powerful jaws and can inject prey with digestive enzymes. The eyes are large and have two focal planes, similar to bifocal glasses. This allows them to see both in and out of water. The front four legs are smaller than in other beetles, while the hind legs are large, flattened, and lined with bristles called setae. The hind legs are used for swimming and propel the beetle through the water like oars, with the setae being adjustable to provide steering and quick changes of direction. Predaceous diving beetles can swim forward and backwards. In addition, some small species can release a jet of water from the rectum to allow for a quick burst of speed. Most species are also strong fliers, able to travel long distances to find new places to inhabit. The majority of diving beetles are 1 to 2.5 cm long, with the largest being the 4.5 cm Megadytes ducalis and the smallest being the 0.8 mm Limbodessus atypicali.

(Image: a predaceous diving beetle seen from below with its legs extended. End ID)

While they are swimmers, predaceous diving beetles need to breathe air. They have a few methods of remaining oxygenated underwater. The first is an ability to trap bubbles of air underneath the elytra, keeping it next to the body where it is intaken through pores called spiracles. The second is an ability to diffuse oxygen in the water into their bodies through their skin. By using these two methods in conjunction, a diving beetle can stay underwater for over a day, though they will have to eventually return to the surface. Some species have developed a third method. These small species have additional setae on the body that are waterproof and act as a sort of net, trapping air around the body. These air bubbles also have to be refilled, but as these are small species, many can refill their air supply using the oxygen released by aquatic vegetation. Beetles using this method have been observed going for up to six weeks without having to return to the surface.

(Image: a predaceous diving beetle at the surface of the water with its back exposed. End ID)

While some members of the family are fully terrestrial and dwell in leaf litter, the majority of predaceous diving beetles are amphibious and can be found on all continents except Antarctica. Most live in freshwater lakes, ponds and slow-moving streams, and wetlands amongst aquatic vegetation. As the name suggests, the beetles are predators. They are voracious and opportunistic hunters who will eat almost anything. While their main targets are invertebrates such as mollusks, worms, and other aquatic insects, they have also been known to attack vertebrates like frogs, tadpoles, and fish. They are also scavengers and cannibals. The beetles will inject the prey with digestive enzymes to kill it while the mouthparts rip apart the food into small enough pieces to swallow. Small prey may be swallowed whole. Diving beetles have a powerful sense of smell/taste (they're kind of the same thing underwater), which they use to detect prey. Diving beetles are also prey to larger animals and they use defenses such as hiding amongst vegetation, biting, and releasing a noxious odor to protect themselves. When diving beetles fly, the do so at night. They are attracted to light and often congregate around street lamps and other light sources. The attraction to light helps them find new water sources by looking for the reflection of the stars and moon below them.

(image: a predaceous diving beetle eating a small fish. The logo for the Smithsonian channel is in the corner. End ID)

Female diving beetles will release pheromones into the water to attract males when they are ready to mate. Males often have cup-like structures on their legs that help them cling onto the female during mating. Mating takes place internally and the female will lay eggs, usually on submerged plants, but some species will lay their eggs on frog egg masses so the larvae have an easy food source. Larval predaceous diving beetles are often called water tigers for how voracious they are. They are elongated, slender insects that don't look very beetle-like at all. Water tigers often get longer than in their adult form. Unlike many species of aquatic insect larvae, water tigers don't have gills, meaning they ave to visit the surface to breathe. They have long snorkel-like tubes on the abdomen that can be used to breathe, allowing the larva to get air while not exposing its whole body. They are primarily ambush predators who will cling onto plants and wait perfectly still until something edible swims by. The larva then grabs the prey and uses its jaws to inject digestive enzymes. It then slurps up the resultant slurry. Once the larva is developed, it will crawl onto land and bury itself in mud to pupate. The pupa stage lasts about a week in most species. After this, the metamorphosis into an adult will be complete and the beetle will dig its way out. Predaceous diving beetles can live for several years, though the life span is heavily dependent on species.

(Image: a water tiger standing on a submerged leaf. It is a long, slender insect with a long, segmented abdomen. It has two large pincers on the dead. The abdomen is curled upwards. End ID)

The conservation needs of predaceous diving beetles is dependent on species, but as a family, they are threatened by habitat loss and pollution. Diving beetles are edible and eaten in multiple countries, including Mexico, Japan, Thailand, Taiwan, and New Guinea. Some species are commercially bred for use as food. Diving beetles are also used in biomedical research as they contain steroids and hormones that are useful to people. Diving beetles may be stocked in ponds or aquariums to eat mosquito larvae and other pests. In eastern Africa, the bite of a diving beetle is a folk remedy that is said to help pubescent children develop. These claims have not been scientifically tested. Additionally, in Zimbabwe, the beetles are goaded to bite the tongues of children in the belief it helps them learn to whistle. Diving beetle bites are painful, but not dangerous to humans.