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Dynastinae or rhinoceros beetles are a subfamily of the scarab beetle family (Scarabaeidae). Other common names – some for particular groups of rhinoceros beetles – are for example Hercules beetles, unicorn beetles or horn beetles. Over 300 species of rhinoceros beetles are known.
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 unicorn beetle (Dynastes tityus).
Description and ecology
The Dynastinae are among the largest of beetles, reaching more than 150 mm (6 in) 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. Their common names 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.
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. Additionally, since they are nocturnal, they avoid many of their predators during the day. When the sun is out, they hide under logs or in vegetation to camouflage themselves from the few predators big enough to want to eat them. If rhinoceros beetles are disturbed, some can release very loud, hissing squeaks. The hissing squeaks are created by rubbing their abdomens against the ends of their wing covers. Rhinoceros beetles are relatively resilient; a healthy adult male can live up to 2-3 years. The females rarely live long after they mate.
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 adult status (see picture at left). The females lay 50 eggs on average. Contrary to what their size may imply, adult rhinoceros beetles do not eat large amounts, unlike their larvae, which eat a significant amount of rotting wood.
Use by humans
Rhinoceros beetles have become popular pets in parts of Asia, due to being relatively clean, easy to maintain, and safe to handle. Also in Asia, male beetles are used for gambling fights. 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 or a small noisemaker is used to duplicate 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.
Some species can become major pests, e.g., in tree plantations. Usually though, beetle population densities are not as high as in some other pest insects, and food trees which are typically already sick or dying from some other cause are preferred. 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 anisopliae is a proven biocontrol agent for beetle infestation in crops.
Dr. MinJun Kim, leading a team of engineers in National Science Foundation-funded research, examined the function and aerodynamics of the Allomyrina dichotoma beetle, 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.
Tribes, with selected genera and species
Agaocephalini Burmeister, 1847 (disputed)
Cyclocephalini Laporte, 1840
Dynastini MacLeay, 1819
- Allomyrina Arrow, 1911 (including Trypoxylus)
- Allomyrina dichotoma – Japanese rhinoceros beetle
- Chalcosoma Hope, 1837
- Dynastes Kirby, 1825
- Eupatorus Burmeister, 1847
- Megasoma Kirby, 1825
- Xylotrupes Hope, 1837
Oryctini Mulsant, 1842
- Coelosis Hope, 1837
- Enema Hope,1837
- Heterogomphus Burmeister, 1847
- Megaceras Hope, 1837
- Oryctes Illiger, 1798
- Strategus Hope, 1837
- Strategus aloeus – ox beetle
- Trichogomphus Burmeister, 1847
Pentodontini Mulsant, 1842
- Bothynus Hope, 1837
- Pentodon Hope, 1837
- Pericoptus Burmeister, 1847
- Thronistes Burmeister, 1847
- Tomarus Erichson, 1847
Phileurini Burmeister, 1847
- Rodger Kram: Inexpensive Load Carrying By Rhinoceros Beetles. The Journal of Experimental Biology 199, 609–612 (1996)
- "Why horn size matters when picking a mate". New Scientist.
- "WHO? KNEW" (May 6, 2005) Current Science Vol.90 No.16
- Rhinoceros beetle gambling in Thailand
- Global Steak - Demain nos enfants mangeront des criquets (2010 French documentary)
- "Engineers Unlock Secrets of Beetle Flight" (news story). ScienceDaily. April 11, 2012.
ScienceDaily (Apr. 10, 2012) — Rhinoceros beetles could play a big part....
- Endrödi S. 1985. The Dynastinae of the World. Dr. W. Junk Publishers
- Dechambre (R.-P.) & Lachaume (G.) The Beetles of the World, volume 27, The genus Oryctes (Dynastidae), Hillside Books, Canterbury 
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