Rhinoceros Beetles

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 1500 species and 225 genera 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 Eastern Hercules beetle (''Dynastes tityus'').

Description and ecology

The Dynastinae are among the largest of beetles, reaching more than 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. An extinct Eocene '' Oryctoantiquus borealis'' was the largest fossil scarabeid, with a length of .Brett Ratcliffe, Dena M. Smith, Diane Marie Erwin.
Oryctoantiquus borealis, New Genus and Species from the Eocene of Oregon, U.S.A., the World's Oldest Fossil Dynastine and Largest Fossil Scarabaeid (Coleoptera: Scarabaeidae: Dynastinae)
. 2009. The Coleopterists Bulletin 59(Mar 2005):127-135 DOI:10.1649/0010-065X(2005)059 127:OBNGAS.0.CO;2 Some modern Oryctini grew up to . 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.

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.

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.

Interactions with humans

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 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.

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.

As pests

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 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 anisopliae'' is a proven biocontrol agent for beetle infestation in crops.

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'' 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; genera:
# '' 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'' – Asiatic 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

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