Dytiscidae

Dytiscidae
Sunburst diving beetle Thermonectus marmoratus (Dytiscinae: Aciliini) inhabiting rock pool at Thiruvannamalai, India
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Superfamily: Dytiscoidea
Family: Dytiscidae
Leach, 1815

The Dytiscidae – based on the Greek dytikos (δυτικός), "able to dive" – are the predaceous diving beetles, a family of water beetles. They are about 25 mm (1.0 in) long on average, though much variation is seen between species. Dytiscus latissimus, the largest,[1] can grow to 45 mm long. Most are dark brown, blackish, or dark olive in color with golden highlights in some subfamilies. They have short, but sharp mandibles. Immediately upon biting, they deliver digestive enzymes. The larvae are commonly known as water tigers. The family has not been comprehensively cataloged since 1920, but is estimated to include about 4,000 species in over 160 genera.

Larvae and development

A predaceous diving beetle larva ("water tiger")

When still in larval form, the beetles vary in size from about 1 to 5 cm (0.5 to 2.0 in). The larval bodies are shaped like crescents, with the tail long and covered with thin hairs. Six legs protrude from along the thorax, which also sports the same thin hairs. The head is flat and square, with a pair of long, large pincers. When hunting, they cling to grasses or pieces of wood along the bottom, and hold perfectly still until prey passes by, then they lunge, trapping their soon-to-be-food between their front legs and biting down with their pincers. Their usual prey includes tadpoles and glassworms, among other smaller water-dwelling creatures.

As the larvae mature, they crawl from the water on the sturdy legs, and bury themselves in the mud for pupation. After about a week, or longer in some species, they emerge from the mud as adults.

Edibility

Adult Dytiscidae, particular of the genus Cybister, are edible. Remnants of C. explanatus were found in prehistoric human coprolites in a Nevada cave, likely sourced from the Humboldt Sink.[2] In Mexico, C. explanatus is eaten roasted and salted to accompany tacos. In Japan, C. japonicus has been used as food in certain regions such as Nagano prefecture. In the Guangdong Province of China, the latter species, as well as C. bengalensis, C. guerini, C. limbatus, C. sugillatus, C. tripunctatus, and probably also the well-known Great diving beetle (D. marginalis) are bred for human consumption, though as they are cumbersome to raise due to their carnivorous habit and have a fairly bland (though apparently not offensive) taste and little meat, this is decreasing. Dytiscidae are reportedly also eaten in Taiwan, Thailand, and New Guinea.[3]

Large but slow on land and not particularly fierce as adults, they are also eaten with relish by many midsized birds, mammals, and other larger predators. The larvae are usually safer, due to their camouflage and ability to escape by water jet; they can be quite hard to catch and may become apex predators in small ponds.

Cultural Significance

The diving beetle plays a role in a Cherokee creation story. According to the narrative, upon finding nowhere to rest in the "liquid chaos" the beetle brought up soft mud from the bottom. This mud then spread out to form all of the land on Earth.[2]

Ethnobiology

Adult Dytiscidae, as well as Gyrinidae, are collected by young girls in East Africa. It is believed that inducing the beetles to bite the nipples will stimulate breast growth.[2]

Systematics

The following taxonomic sequence gives the subfamilies, their associated genera.[4]

Subfamily Agabinae Thomson, 1867

Subfamily Colymbetinae Erichson, 1837

Subfamily Copelatinae Branden, 1885

Subfamily Coptotominae Branden, 1885

Subfamily Dytiscinae Leach, 1815

Subfamily Hydrodytinae K.B.Miller, 2001

Subfamily Hydroporinae Aubé, 1836

Subfamily Laccophilinae Gistel, 1856

Subfamily Lancetinae Branden, 1885

Subfamily Matinae Branden, 1885

Subfamily Incertae sedis

References

  1. ↑ http://www.hurdan.com/search?q=dytiscidae
  2. 1 2 3 Miller, Kelly; Bergsten, Johannes (3 October 2016). Diving Beetles of the World: Systematics and Biology of the Dytiscidae. Baltimore: Johns Hopkins University Press. p. 20.
  3. ↑ De Foliart (2002), Jäch (2003), CSIRO (2004)
  4. ↑ Dytiscidae Species List at Joel Hallan's Biology Catalog. Texas A&M University. Retrieved on 7 May 2012.
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