Geodorcus ithaginis
| Geodorcus ithaginis | |
|---|---|
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Family: | Lucanidae |
| Genus: | Geodorcus |
| Species: | G. ithaginis |
| Binomial name | |
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Geodorcus ithaginis (Broun, 1893) |
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| Synonyms | |
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Lissotes ithaginis Broun, 1893 |
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Lissotes ithaginis Broun, 1893
Geodorcus ithaginis, the Mokohinau stag beetle, is a large flightless species of stag beetle in the family Lucanidae. It was described by Thomas Broun in 1893 after being discovered in the Mokohinau Islands by P. Stewart Sandager, a lighthouse keeper on the islands. The species survives only on the small unnamed island "Stack H", in an patch of vegetation the size of a living room, and is in extreme danger of extinction.
Including their large mandibles (used for fighting over mates), male specimens range in length from 25.5 to 32.8 mm and are 10.4–12.4 mm wide. Females range in length from 20.0–22.5 mm. Their exoskeleton is black and ranges from dull to moderately glossy. The thorax is back, glossy, and wider than it is long. The elytra are rounded at the posterior, almost equally long and wide, and covered in short branching hairs. Male beetles have three teeth at the apex of the mandibles; females have two. What distinguishes this species from all other New Zealand stag beetles is a long conical vertical tooth, on the top of the mandible, in both sexes.
This species is only known from the Mokohinau Islands in New Zealand. Its type locality was given by Broun as "Halodroma Islet", but there is no island by that name. "Halodroma" may be another name for Lizard Island, a small flat island southeast of Burgess Island;Halodroma urinatrix is the former name of Pelacanoides urinatrix, the diving petrel, which used to nest in burrows on Lizard and two other low Mokohinau islands.
G. ithaginis has been collected in recent times from "Stack H", a 1.2 ha island southwest of Burgess Island. All recent surveys have only found this species in a "living-room sized" patch of New Zealand ice plant or horokaka (Disphyma australe) on Stack H; it has not been seen on Lizard Island since its description in 1893.
Geodorcus species on mainland New Zealand are associated with rotten logs, but these are absent from Stack H. The Mokohinau Islands are generally very arid, with poor moisture retention. This beetle burrows into a peat-like layer of soil formed by New Zealand ice plant (Disphyma australe). It has also been found under rocks, in the tussock grass Chionochloa bromoides, and in the leaf litter beneath coastal pohutukawa.
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