|Male Hercules beetle, Dynastes hercules|
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The Hercules beetle (Dynastes hercules, Dynastinae) is a species of rhinoceros beetle native to the rainforests of Central America, South America, and the Lesser Antilles, and is the longest extant species of beetle in the world.
D. hercules has a complex taxonomic history and has been known by several synonyms. It is in the subfamily Dynastinae (rhinoceros beetles) in the larger family Scarabaeidae (commonly known as scarab beetles). Not counting subspecies of D. hercules, seven other species are recognised in the genus Dynastes.
- Dynastes hercules ecuatorianus Ohaus, 1913
- Dynastes hercules hercules (Linnaeus, 1758)
- Dynastes hercules lichyi Lachaume, 1985
- Dynastes hercules morishimai Nagai, 2002
- Dynastes hercules occidentalis Lachaume, 1985
- Dynastes hercules paschoali Grossi & Arnaud, 1993
- Dynastes hercules reidi Chalumeau, 1977 (= baudrii Pinchon, 1976)
- Dynastes hercules septentrionalis Lachaume, 1985 (= tuxtlaensis Moron, 1993)
- Dynastes hercules takakuwai Nagai, 2002
- Dynastes hercules trinidadensis Chalumeau & Reid, 1995 (= bleuzeni Silvestre and Dechambre, 1995)
Adult body sizes vary between 50 and 85 mm in length and 29 and 42 mm in width, though male Hercules beetles may reach up to 17.5 cm in length (including the horn), making them the longest species of beetle in the world. The size of this horn is naturally very variable; more so than any variation of the size of legs, wings, or overall body size in the species. This variability results from developmental mechanisms that couple genetic predisposition with nutrition, stress, exposure to parasites, and/or physiological conditions.
The body of males is black with the exception of the elytra, which can have shades of olive-green. They have a black suture with sparsely distributed black spots elsewhere on the elytra. D. hercules is highly sexually dimorphic, with only males exhibiting the characteristic horn. They have a slightly iridescent colouration to their elytra, which varies in colour between specimens and may be affected by the humidity of the local environment in which they develop. Females of D. hercules have punctured elytra which are usually entirely black, but sometimes have the last quarter coloured in the same way as the males.
Distribution and habitat
Populations of D. hercules may be found from southern Mexico south to Bolivia in mountainous and lowland rainforests. Known populations include the Lesser Antilles, Trinidad and Tobago, Brazil, Ecuador, Colombia, and Peru. Chromosomal analysis has shown that the genus Dynastes in fact originated from South America.
Not much is known about the life cycle in the wild, but much evidence has been gained through observations of captive-bred populations. Females of D. hercules may lay up to 100 eggs on the ground or on dead wood. Once hatched, the larval stage of the Hercules beetle may last up to two years in duration, with the larva growing up to 4.5 in (11 cm) in length and weighing more than 100 g. The larvae undergo three instars. In laboratory conditions at 25 ± 1°C, the first stage lasts an average of 50 days, the second stage an average of 56 days, and the third an average of 450 days. The pupal stage lasts about 32 days, while adults can live for three to six months in captivity.
The mating season for adults typically occurs during the rainy season (July to December). Females have an average gestation period of 30 days from copulation to egg-laying. Male Hercules beetle typically use their large horns to settle mating disputes; these fights can cause significant physical damage to the combatants. During fights, the males attempt to grab and pin their rival between the cephalic and thoracic horns to lift and throw them. The successful male wins mating rights with the female, though the beetles remain polygynandrous.
Diet and behaviour
The larva of the Hercules beetle feeds on rotting wood during its two-year larval stage. The adult Hercules beetle feeds on fresh and rotting fruit. They have been observed feeding on peach, pear, apple, and grape in captivity.
Within their native rainforest habitats, larvae reside in decaying wood, and the adult beetles, which are nocturnal, forage for fruit at night and hide or burrow within the leaf litter during the day.
Like most insects, communication within the species is a mix of chemoreception, sight, and mechanical perception. Experiments on D. hercules have shown that a male placed in the vicinity of a female will immediately orient towards her and seek her out, suggesting chemical communication through strong sexual pheromones.
Reports suggest the Hercules beetle is able to carry up to 850 times its body mass, but actual measurements on a much smaller (and relatively stronger: see square-cube law) species of rhinoceros beetle shows a carrying capacity only up to 100 times their body mass, at which point they can barely move.
Relationship to humans
D. hercules does not negatively affect human activities, either as an agricultural pest or disease vector. The beetles may be kept as pets.
- Huang, J. (2016). "Parapatric genetic introgression and phenotypic assimilation: testing conditions for introgression between Hercules beetles (Dynastes, Dynastinae)". Molecular Ecology. 25: 5513–5526. doi:10.1111/mec.13849.
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- Krell, F., Krell, V. Longevity of the Western Hercules beetle, D. grantii Horn (Coleoptera: Scarabaeidae: Dynastinae). The Coleopterists Bulletin, vol. 69, 2015, 1p.
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- Kram, R. (1996). "The Journal of Experimental Biology" (PDF). 199: 609–612.
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