Thermonectus marmoratus
Thermonectus marmoratus is a relatively colorful North American species of diving beetle known by the common names sunburst diving beetle and yellow-spotted diving beetle. The behavior of this diving beetle has been compared to a scuba diver, since it carries with it a bubble of air as it dives down into the water. Its aquatic larval stage was the first ever recorded use of bifocals in the animal world. The beetle uses in its principal eyes two retinas and two distinct focal planes that are substantially separated, in the manner of bifocals to switch their vision from up-close to distance, for easy and efficient capture of their prey.
Because of their bright aposematic colors, they are often displayed in zoos, sometimes together with Abedus herberti and other aquatic beetles.
Physical description
The adult beetle has a length of, with females slightly larger than males. The sunburst diving beetle has a black and streamlined carapace covered with bright yellow or golden spots. The male has a suction disk on each foreleg.Colors and protection
The sunburst diving beetle's distinctive yellow spots on a black background serve as a warning sign to predators that the insect can release a foul tasting chemical. The milky appearing chemical is ejected from specialized glands found behind the insect's head, and has been found to be made primarily out of the steroid hormones cybisterone and mirasorvone. It has been further hypothesized that mirasorvone functions as a fish deterrent.Behavior
Diet
Sunburst diving beetles are predators and scavengers of small animals, especially invertebrates such as other aquatic insects and snails, but also small vertebrates such as young fish and tadpoles. If available, they prefer to feed on small, already dead soft-bodied animals. These beetles are useful because they eat mosquito larvae and pupae. They have also been observed swarming a prey item and feeding en masse. In captivity, these beetles will feed on flake fish food and live crickets.Swimming
Sunburst diving beetles live in water and swim well. The diving beetle swims by thrusting its hind legs simultaneously, and can remain underwater for extended periods of time by storing an air bubble beneath its wings.Distribution and habitat
Sunburst diving beetles are found in extreme Southern California, southern Utah, Arizona, New Mexico and Texas in the United States, and in Mexico.They inhabit various slow-moving freshwater habitats, especially shallow, temporary or intermittent pools and creeks with little or no aquatic vegetation. When their water source dries up they will fly to a new one.