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Common Name:

Spotted or Sunburst Diving Beetle

Scientific Name:

Thermonectus mamoratus

Size:

These high-powered diving insects reach a maximum length of 0.5 inches (10 mm).

Description:

Sunburst Diving Beetles are small turtle-like members of the order Coleoptera. They belong to the Dytiscidae family which are a large predaceous family of beetles found worldwide (Morgan, 1992). Sunburst Diving Beetles are characterized by having a black carapace covered with bright yellow spots. Their streamline body aids in swimming effortlessly through the water. Morgan (1992) has noted a sexual dimorphism in this species with the females averaging slightly larger than the males. Furthermore, males have a suction disk on their forelegs.

Behavior:

Sunburst Diving Beetles are proficient swimmers using their powerful hind limbs to propel them through the water. They are winged animals, which allows them to travel to other areas when the pond they inhabit dries up. These diving beetles are active year round; central to their activity is the presence of a water source. When the summer monsoon season arrives, many temporary ponds are inhabited by these diving beetles. They share these water environs with other larger predators such as the Giant Water Bug (Abedus americanus) and the Ferocious Water Bug (Abedus herberti). These beetles are capable of delivering a bite which can sting; but are not prone to bite. In fact, one of us (BT) has only been bitten once in over ten years of working with these beetles.

Sunburst Diving Beetles undergo complete metamorphosis. They usually lay their eggs in sand. The eggs hatch into what are known as water tigers and feed on small invertebrates such as Daphnia.The larvae pupate and eventually the adult emerges. These diving beetles are usually ready to breed a few weeks after emerging from the pupae.

Habitat:

Sunburst Diving Beetles are found in extreme Southern California, Arizona, New Mexico, Texas, and Mexico. They require at least a temporary water source. If the one they inhabit dries up, these diving beetles will fly until another water source is located for them to inhabit.

Prey

In the wild, these beetles feed on other invertebrates including mosquito larvae and pupae (Morgan, 1992). Spotted Diving Beetles have also been observed swarming a prey item and feeding en mass. In captivity, these beetles will feed on flake fish food and live crickets.

Captive Care:

Sunburst Diving Beetles do very well in captivity. They can be kept in small groups if enough food is provided for them. Failure to keep the colony adequately fed will result in cannibalism. We have kept up to 50 diving beetles in a ten-gallon aquarium utilizing a simple filtration system to keep the water clean. A third of the water should be changed every week or so. Once every four months, the entire tank should be cleaned with fresh water. Sunburst Diving Beetles can live in tap water provided the water has had time to sit and "age." Several rocks or other types of perches should be kept in the cage for the beetles to climb up on if the need arises. Because these beetles can fly, an escape-proof cage is imperative! These beetles should be fed four or five times weekly. Any leftover food items should be removed to prevent water stagnation.

References:

ARNETT JR, R.H. & JACQUES JR., R.L. (1981), "Thermonectus marmoratus," Simon and Schuster's Guide to Insects. Simon and Schuster Inc., New York, Toronto and London, pp. 86-87.

EVANS, D.L. AND SCHMIDT, J.O.;EDs. (1990), Insect Defenses, Adaptive Mechanisms and Strategies of Prey and Predators. State Univ. of New York Press, Albany, 482 pp.

MILNE, L, AND MILNE, M. (1980), "Marbled Diving Beetle (Thermonectus marmoratus)," The Dobbin Society Field Guide to North American Insects and Spiders. Alfred A. Knopf, NY, p. 542+ plate 96.

MORGAN, R.C. (1988), "Windows on the Water World," Backyard BUGwatching 5:4-6.

MORGAN, R.C. (1992B), "Natural History, Captive Management and Display of the Sunburst Diving Beetle Thermonectus marmoratus," AAZPA/CAZPA Annual Conference Proceedings 1992:457-464.