Moellenkampi Beetle

Appearance

Chalcosoma moellenkampi can reach about the same size as C. atlas, and very large males may measure up to 110 mm (4.3 in) from the tip of the head horn to the end of the elytra (wingcases). The largest specimen in the genus is Chalcosoma caucasus, where males may occasionally reach 130 mm in total length. Unlike the males, which in Chalcosoma can be distinguished from each other using the characteristics listed below, females are very similar in the three Chalcosoma species, and can usually only be distinguished from each other by specialists.

Atlas beetle males are renowned for their three horns, two on the pronotum and one on the head. Owing to environmental conditions, not all larvae grow to similar sizes, and in those which have lived under less favorable conditions, adult beetles become small. In small males, the horns are very short and the head horn extends almost vertically upwards and usually has three small prongs, but in large males, the horns are enormous, and the head horn projects mainly anteriorly with an upwards curvature. The size of the horns relative to the size of the beetle is thus positively allometric, meaning the horns are much larger relative to the body size of the beetle in large males compared to small males, which have very short horns. In contrast, females do not show such dramatic differences in body proportions, and large females are simply larger versions of small females.

Large male Atlas beetles are some of the largest and most impressive beetles in the world, and the metallic lustre of their wingcases only adds to their beauty. Chalcosoma moellenkampi can be distinguished from its two close relatives by a more narrow pronotum on which the pronotum horns are set more closely together, whereas the horns in C. atlas and C. caucasus extend from the lateral sides of the pronotum. Also, in large males with huge horns, the head horn is always shorter than the lateral pronotum horns in Chalcosoma atlas and C. caucasus, but in C. moellenkampi the head horn often extends somewhat anteriorly to the pronotum horns. The pronotum horns are also turned distinctly downwards in C. moellenkampi, and the head horn lacks the large dorsal peg seen in C. caucasus or the terminal widening usually present in C. atlas. C. moellenkampi is usually less lustrous than the other two species of Chalcosoma.

Distribution

Unlike its close relatives, C. atlas and C. caucasus, C. moellenkampi has a rather restricted geographic distribution and appears to occur only on Borneo.

Behavior

As the other species of Atlas beetles, large males in C. moellenkampi are very aggressive towards other males, but small males are more peaceful, lacking the body size and large horns to fight. Unlike the great differences in horn size at different body sizes, the size of the male genitalia, known as parameres, do not vary nearly as much in large and small males, implying males of all sizes can still mate with females.[5] In the wild, the Chalcosoma species live in rainforests and palm plantations, and males and females typically meet at feeding sites, for instance wounded trees, where the beetles drink the sap. They reach new areas by flying around at night. At the feeding sites, large males will attempt to dominate the site by sheer size, and smaller males are chased away. The dominance will ensure the big males' mating rights with any females which come to the site. However, if two equally large males meet, neither is usually prepared to back away and they will fight each other using their large horns, while also trying to trip the opponent with their long front legs. A male will attempt to pin a rival between the head horn, which can be moved upwards or downwards as the beetle raises or lowers its head, and the two pronotum horns. The beetle will then attempt to throw its rival off the branch or throw it on its back. In other beetles in which only large males have big horns and are aggressive, small males rely on stealth tactics instead, avoiding physical confrontation with the large males, and instead try to mate with females while the large males are busy fighting each other.[6] While such behavior has not been reported from the wild for C. moellenkampi, it is known for C. atlas and it is probably present in C. moellenkampi, as well, since the two speciess are closely related and very similar in other life history aspects.

This violent temper also means that in captivity, males cannot be placed in the same vivarium, as this will cause them to engage in violent fights, which may cause physical injury. The species is less common among beetle hobbyists than C. atlas, and the breeding ecology is therefore less well known in C. moellenkampi, but C. atlas larvae are unusual among rhinoceros beetles by being quite aggressive and willing to bite if touched, and larvae of C. moellenkampi may share this behavior. Females burrow into the soil or into old rotting hardwood logs to lay eggs. The larvae go through three stages of development, and may reach a massive weight of 100 g. At the end of larval stage 3, the larva creates a large, oval coccoon of decayed wood and earth, where it transforms into a pupa, which hatches out in another two months. The total generation span from egg to adult beetle may take 13-18 months.