Dynastinae

Dynastinae; Temporal range: Eocene–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Scarabaeidae
Subfamily:	Dynastinae; MacLeay, 1819
Tribes
	See text

Dynastinae or rhinoceros beetles are a subfamily of the scarab beetle family (Scarabaeidae). Other common names – some for particular groups of rhinoceros beetles – include Hercules beetles, unicorn beetles or horn beetles. Over 1,500 species and 225 genera of rhinoceros beetles are known.^[2]

Many rhinoceros beetles are well known for their unique shapes and large sizes. Some famous species are, for example, the Atlas beetle (Chalcosoma atlas), common rhinoceros beetle (Xylotrupes ulysses), elephant beetle (Megasoma elephas), European rhinoceros beetle (Oryctes nasicornis), Hercules beetle (Dynastes hercules), Japanese rhinoceros beetle or kabutomushi (Allomyrina dichotoma), ox beetle (Strategus aloeus) and the Eastern Hercules beetle (Dynastes tityus).

Description

The Dynastinae are among the largest of beetles, reaching more than 15 centimetres (6 inches) in length, but are completely harmless to humans because they cannot bite or sting. Some species have been anecdotally claimed to lift up to 850 times their own weight.^[3] An extinct Eocene Oryctoantiquus borealis was the largest fossil scarabeid, with a length of 5 centimetres (2.0 in).^[4] Some modern Oryctini grew up to 7 cm (3 in).^[4] Common names of the Dynastinae refer to the characteristic horns borne only by the males of most species in the group. Each has a horn on the head and another horn pointing forward from the center of the thorax. The horns are used in fighting other males during mating season, and for digging. The size of the horn is a good indicator of nutrition and physical health.^[5]

The body of an adult rhinoceros beetle is covered by a thick exoskeleton. A pair of thick wings lie atop another set of membranous wings underneath, allowing the rhinoceros beetle to fly, although not very efficiently owing to its large size. Their best protection from predators is their size and stature, also avoiding many due to being nocturnal. When the sun is out, they hide under logs or in vegetation to camouflage themselves from the few predators big enough to eat them. If rhinoceros beetles are disturbed, some can release very loud, hissing squeaks created by rubbing their abdomens against the ends of their wing covers.

Ecology

These beetles' larval stages can be several years long. The larvae feed on rotten wood and the adults feed on nectar, plant sap, and fruit. First, the larvae hatch from eggs and later develop into pupae before they reach adulthood.

Mating

Male Japanese rhinoceros beetles (Allomyrina dichotoma) fight to dominate sap sites. Males use their horns to pry rival males off the area, which also may give them the chance to mate with a female. In this and other species that defend mating sites, larger males with larger horns mate more frequently, as they win more contests. Small males often avoid larger males and exhibit alternative strategies to gain access to females.^[6]^[7]

As pests

Some species, such as the coconut rhinoceros beetle (Oryctes rhinoceros), can become major pests, e.g., in tree plantations.^[8] Usually though, beetle population densities are not as high as in some other pest insects, and they typically prefer food trees which are already sick or dying from some other cause. Some species' larvae, however, will attack healthy trees or even root vegetables, and when they occur in large numbers, can cause economically significant damage. The fungus Metarhizium majus is a proven biocontrol agent for beetle infestation in crops.

Uses

Rhinoceros beetles have become popular pets in parts of Asia,^[9] due to being relatively clean, easy to maintain, and safe to handle. Also in Asia, male beetles are used for gambling fights.^[10] Since males naturally have the tendency to fight each other for the attention of females, they are the ones used for battle. To get the two male beetles to lock in combat, a female beetle is used, or a small noisemaker duplicating the female's mating call.

Entomologist Séverin Tchibozo suggests the larvae contain much more protein (40%) than chicken (20%) and beef (approximately 18%), and they could become a protein source for a large human population.^[11]

Dr. MinJun Kim, leading a team of engineers in National Science Foundation-funded research, examined the function and aerodynamics of Allomyrina dichotoma with the help of researchers in Drexel University's Mechanical Engineering Department and in collaboration with Konkuk University in South Korea. Rhinoceros beetles could play a big part in the next generation of aircraft design.^[12]

Tribes with selected genera and species

Agaocephalini

Auth: Burmeister, 1847. all genera:

Aegopsis Burmeister, 1847
Agaocephala Lepeletier & Audinet-Serville, 1828
Antodon Brême, 1845
Brachysiderus Waterhouse, 1881
Colacus Ohaus, 1910
Democrates (beetle) Burmeister, 1847
Gnathogolofa Arrow, 1914
Horridocalia Endrödi, 1974
Lycomedes (beetle) Breme, 1844
Mitracephala Thomson, 1859
Spodistes Burmeister, 1847

Cyclocephalini

Auth: Laporte, 1840. Selected genera:

Ancognatha Erichson, 1847
Cyclocephala Dejean, 1821 (masked chafers)
Dyscinetus Harold, 1869 (rice beetles)

Dynastini

Auth: MacLeay, 1819. Selected genera:

Allomyrina Arrow, 1911 (including Trypoxylus)
- Allomyrina dichotoma – Japanese rhinoceros beetle
Chalcosoma Hope, 1837
- Chalcosoma atlas – Atlas beetle
- Chalcosoma moellenkampi – Moellenkampi beetle
- Chalcosoma caucasus – Caucasus beetle
Dynastes MacLeay, 1819
- Dynastes hercules – Hercules beetle
- Dynastes neptunus – Neptune beetle
Eupatorus Burmeister, 1847
- Eupatorus gracilicornis – Five-horned rhinoceros beetle
- Eupatorus siamensis – Siamese beetle
- Eupatorus birmanicus – Rabbit beetle
Megasoma Kirby, 1825
- Megasoma mars - Mars beetle
- Megasoma elephas - Elephant beetle
- Megasoma actaeon - Actaeon beetle
Xylotrupes Hope, 1837
- Xylotrupes gideon – Siamese rhinoceros beetle
- Xylotrupes ulysses

Hexodontini

Auth. Lacordaire, 1856; all genera from Madagascar:

Hemicyrthus Reiche, 1860
Hexodon Olivier, 1789
Hyboschema Péringuey, 1901

Oryctini

Auth: Mulsant, 1842. Selected genera:

Enema Hope, 1837
Megaceras Hope, 1837
- Megaceras briansaltini
Oryctes Hellwig, 1798
- Oryctes nasicornis – European rhinoceros beetle
- Oryctes rhinoceros – coconut rhinoceros beetle
Strategus Kirby, 1828
- Strategus aloeus – ox beetle
Trichogomphus Burmeister, 1847
Xyloryctes

Oryctoderini

Auth. Endrödi, 1966; all genera:

Chalcasthenes Arrow, 1937
Chalcocrates Heller, 1903
Coenoryctoderus Prell, 1933
Hatamus Sharp, 1877
Melanhyphus Fairmaire, 1881
Neohyphus Heller, 1896
Onychionyx Arrow, 1914
Oryctoderinus Endrödi, 1978
Oryctoderus Boisduval, 1835
Paroryctoderus Dechambre, 1994

Pentodontini