Tuesday, 26 February 2013

Beetles and Bugs 2: Big in Japan

D.hercules (male)
The Purple Jewel Beetles I wrote about last week belong to the subfamily Cetoniinae of the Scarabeidae, the scarab beetles. Related to them, but far larger (they include the largest and heaviest of all insects) are the giant Rhinoceros and Stag beetles of the related subfamily Dynastinae. Keeping beetles of all sizes is a popular hobby in Japan, and as a result a surprising number of these magnificent insects are now bred in captivity. The whole group of Rhinoceros beetles all over the world are marked by the extravagant head ornaments of the males, which use their decorations in fights over access to females. Part of the reason they are popular in Japan is that contests are staged between pet beetles like real life versions of Pokemon.

D.hercules (female)
As a group, Rhinoceros beetles are heavily associated with rotten wood, as this is the food source for their larvae. Dead wood is not exactly nutritious, and as a result the life cycle is usually very long, with the larger species taking several years to reach maturity and emerge as adults. The adults generally feed on sap, gum, and fallen fruit. An individual adult has a lifespan of several months, which gives the female time to travel and locate suitable dead wood over a wide area. As a result of this habitat requirement, old mature forest is required for them to survive, and deforestation is a threat to the less widely distributed forms. In many cases the larvae seem to require a fairly narrow range of wood types, probably because they derive a lot of their actual nutrition from the fungi that are decomposing the wood, and these can be quite host-specific. In captivity, they tend to be raised on rotting oak, birch, maple, and other deciduous trees.

D.tityus (Eastern US)
The Dynastes beetles (there are around eight species) are found mostly in Central and South America, although two species, D.tityus and D.granti are found in the forests of North America as far north as New York.The northern forms are smaller, but still reach 30mm wide and (in males at least) 60mm long. Here at Bristol, we have shown the Hercules beetle, Dynastes hercules, on many occasions. Unfortunately we do not currently have any adults on show, but with any luck we may have some emerge later in the year. D.hercules is found in Central and South America, but there is one report as far north as Arizona. It is quite variable across its range, and the adults can also differ in size depending on the quality of food available to the developing larvae. A really large male can be 17cm long including the horns.

For a video of wild D.hercules, see here:

Hercules beetles are fairly well armoured creatures, and do not seem to have a lot of natural predators. The grubs are also well protected inside rotting logs or deep in the litter layer – females in captivity seem to need to dig down at least 30cm to lay their eggs. As a result, they are not especially prolific, with a female laying perhaps 50 eggs in her lifetime.

D.hercules - final instar larva
For a complete guide to raising these and similar beetles, a good online guide can be found here:

(images from wikipedia)

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