Dynastinae

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.[2]

Dynastinae
Temporal range:
Rhinoceros Beetle
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Scarabaeidae
Subfamily: Dynastinae
MacLeay, 1819
Tribes

See text[1]

European rhinoceros beetle

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
European rhinoceros beetle – three stages from larva to adult:
Larva (back), pupa (center), imago (front)

The Dynastinae are among the largest of beetles, reaching more than 15 cm (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.[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 centimetres (2.8 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. 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.[6][7]

Interactions with humans

Use by humans

Rhinoceros beetles have become popular pets in parts of Asia,[8] due to being relatively clean, easy to maintain, and safe to handle. Also in Asia, male beetles are used for gambling fights.[9] 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.[10]

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.[11]

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 majus is a proven biocontrol agent for beetle infestation in crops.

Tribes with selected genera and species

Agaocephalini
Antodon goryi

Auth: Burmeister, 1847. all genera:

  1. Aegopsis Burmeister, 1847
  2. Agaocephala Lepeletier & Audinet-Serville, 1828
  3. Antodon Brême, 1845
  4. Brachysiderus Waterhouse, 1881
  5. Colacus Ohaus, 1910
  6. Democrates (beetle) Burmeister, 1847
  7. Gnathogolofa Arrow, 1914
  8. Horridocalia Endrödi, 1974
  9. Lycomedes (beetle) Breme, 1844
  10. Mitracephala Thomson, 1859
  11. Spodistes Burmeister, 1847

Cyclocephalini
Cyclocephala borealis (Cyclocephalini)

Auth: Laporte, 1840. Selected genera:

Dynastini
Eupatorus gracilicornis (Dynastini)

Auth: MacLeay, 1819. Selected genera:

Hexodontini

Auth. Lacordaire, 1856; genera:

  1. Hemicyrthus Reiche, 1860
  2. Hexodon Olivier, 1789
  3. Hyboschema Péringuey, 1901

Oryctini
Trichogomphus mongol (Oryctini)

Auth: Mulsant, 1842. Selected genera:

Oryctoderini

Auth. Endrödi, 1966; all genera:

  1. Chalcasthenes Arrow, 1937
  2. Chalcocrates Heller, 1903
  3. Coenoryctoderus Prell, 1933
  4. Hatamus Sharp, 1877
  5. Melanhyphus Fairmaire, 1881
  6. Neohyphus Heller, 1896
  7. Onychionyx Arrow, 1914
  8. Oryctoderinus Endrödi, 1978
  9. Oryctoderus Boisduval, 1835
  10. Paroryctoderus Dechambre, 1994

Pentodontini
Pentodon idiota (Pentodontini)

Auth: Mulsant, 1842. Selected genera:

Phileurini
Phileurus valgus (Phileurini)

Auth: Burmeister, 1847; selected genera:

  • Cryptodus MacLeay, 1819
  • Phileurus Latreille, 1807

Notes
  1. Bouchard, P., Y. Bousquet, A. Davies, M. Alonso-Zarazaga, J. Lawrence, C. Lyal, A. Newton, et al. (2011). "Family-group names in Coleoptera (Insecta)". ZooKeys, vol. 88, 1-972.
  2. Beutel, Rolf G.; Leschen, Richard A.B., eds. (2016-03-21). Coleoptera, Beetles, Volume 1, Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim). De Gruyter. doi:10.1515/9783110373929. ISBN 978-3-11-037392-9.
  3. Kram, Rodger (1 March 1996). "Inexpensive load carrying by rhinoceros beetles". Journal of Experimental Biology. 199 (3): 609–612. doi:10.1242/jeb.199.3.609. PMID 9318326.
  4. 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[0127:OBNGAS]2.0.CO;2
  5. "Why horn size matters when picking a mate". New Scientist.
  6. Buchalski, Benjamin; Gutierrez, Eric; Emlen, Douglas; Lavine, Laura; Swanson, Brook (15 October 2019). "Variation in an Extreme Weapon: Horn Performance Differences across Rhinoceros Beetle (Trypoxylus dichotomus) Populations". Insects. 10 (10): 346. doi:10.3390/insects10100346. PMC 6835817. PMID 31618906.
  7. Goczał, Jakub; Rossa, Robert; Tofilski, Adam (17 April 2019). "Intersexual and intrasexual patterns of horn size and shape variation in the European rhinoceros beetle: quantifying the shape of weapons". Biological Journal of the Linnean Society. 127 (1): 34–43. doi:10.1093/biolinnean/blz026.
  8. "WHO? KNEW" (May 6, 2005) Current Science Vol.90 No.16
  9. Rhinoceros beetle gambling in Thailand
  10. Global Steak - Demain nos enfants mangeront des criquets (2010 French documentary)
  11. "Engineers Unlock Secrets of Beetle Flight" (news story). ScienceDaily. April 11, 2012. ScienceDaily (Apr. 10, 2012) — Rhinoceros beetles could play a big part....

Further reading
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