FNZ 61 - Lucanidae (Insecta: Coleoptera) - Popular summary
Holloway, BA 2007. Lucanidae (Insecta: Coleoptera). Fauna of New Zealand 61, 254 pages.
( ISSN 0111-5383 (print), ; no. 61. ISBN 978-0-478-09395-7 (print), ). Published 21 Nov 2007
The Lucanidae is a small diverse family distributed worldwide, with about 110 genera and about 1300 described species. The New Zealand lucanid fauna comprises 39 species of which 35 are endemic and belong in 5 endemic genera, and 4 are foreign, 3 being from Australia and 1 originating from Taiwan. Two of the Australian species are known to be breeding in New Zealand, but it is very unlikely that the third Australian species and the one from Taiwan are established here.
When first described and until almost the end of last century most of the New Zealand species were assigned to the Australian genera Ceratognathus and Lissotes, and to the mainly northern hemisphere genus Dorcus, because of superficial morphological similarities. However, in the late 1990s comparative studies of the male and female genitalia and elytral surface structures indicated that the New Zealand species were not congeneric with the Australian species nor with those in Dorcus so 3 new genera, Geodorcus, Holloceratognathus and Paralissotes were established for some of the species and the remainder were placed in the reinstated New Zealand genus Mitophyllus. These 4 genera encompass 34 of the 35 endemic species. The remaining species is in Dendroblax, a particularly interesting genus because it belongs in the very small subfamily Lampriminae found only in the southern hemisphere. Geodorcus and Paralissotes belong in the large, worldwide subfamily Lucaninae and Holloceratognathus and Mitophyllus are in Aesalinae, a much smaller subfamily represented in both hemispheres. The New Zealand genera are not morphologically very close to others in their subfamilies.
In some parts of the world, especially in the northern hemisphere and tropics, the family includes large spectacular species, easily recognised as stag beetles by the long tusk-like or antler-like mandibles of males. Many people living in these areas are familiar with them because on hot summer evenings they often fly to lights and enter houses. Consequently stag beetles have become an important part of the folklore and artistry of some European countries, and in parts of Asia they may even be kept as pets. The endemic New Zealand stag beetles by comparison are inconspicuous and rather cryptic, most spending their entire lives in native habitats and having to be searched for to be seen. They are neither brightly coloured nor shiny, instead have dullish brown or black integument, sometimes with tufts or patches of yellowish or brown scales or hairs. The genus Geodorcus has the largest specimens, some males measuring 44 mm in length including mandibles and about 34 mm excluding mandibles, but the maximum length of males in the other genera is about 20 mm. The overall length of females is usually much less than that of males of the same species mainly because their mandibles are shorter. All the species of Geodorcus and Paralissotes and females of 1 species of Mitophyllus are unable to fly because their wings are reduced to vestiges, but the other New Zealand lucanids have fully functional wings.
Fully winged adults of a few species of Mitophyllus are occasionally found out in the open in the vicinity of houses and well away from forests. They have been able to extend their ranges into parks and gardens because their larvae can develop in dead trunks and branches of cultivated native trees such as species of Pittosporum and in exotics such as figs and apples. The trees are considered to be the hosts but the species of fungi developing inside their branches have a more important role to play because they convert the wood to a substrate that will sustain the larvae throughout their development. Without having the right species of fungi the wood will not be attractive to the beetles. Nothing is known about the food of Mitophyllus adults but it is likely to be nectar. Adults of Geodorcus spend their entire lives in total darkness or twilight conditions, staying in cool damp places under logs and rocks or in accumulated damp leaves during the day and emerging at night or sometimes on dull rainy days to feed on exudations either from tree trunks or from low-growing plants. Their larvae are subterranean and consume vast quantities of soil. Spectacular size ranges of adults in some Geodorcus species probably result from the quality and abundance of larval food, the largest males of the most widespread species, G. helmsi, for example, being found on islands where their larvae live in soils that are greatly enriched by abundant sea bird guano.
The geographical distribution of the endemic species depends to some extent on whether they are fully winged or flightless, but other factors such as the time spent and area covered searching for specimens and the chances of being in the right place at the right time, have to be kept in mind when distribution maps are being viewed. At the present time, Mitophyllus irroratus and M. parrianus are the only stag beetles found in the North and South Islands and in Stewart I. M. irroratus is present as well on the Kermadec Islands. Of the remaining Mitophyllus species 4 have been found in the North and South Islands, 4 are known only from the North Island, 3 only from the South Island, and 1 is found only in the Chathams. One species of the fully winged genus Holloceratognathus has been collected in the North and South Islands, l is found in both islands and in the Chathams, and the 3rd, associated with ants, is known only from a small area in the south of the North Island. The single species of Dendroblax is distributed from Northland to the Otago Lakes area. All the Paralissotes species are flightless. The most common and wide ranging species, P. reticulatus, has been found from the Bay of Plenty to South Canterbury, but the remaining 6 species are much less widespread, 1 being found only in the Three Kings, 4 only in the North Island, and 1 is confined to the north of the South Island. Apart from Geodorcus helmsi, already mentioned, whose range extends down the western side of the South Island to the muttonbird islands south of Stewart Island most Geodorcus species have even more restricted ranges. Two are endemic to islands in the Chatham archipelago, 4 are confined to the North Island, and 3 to the South Island, and within these generalised areas some species are known only from single mountain tops or islands. As the adults are unable to fly to new sites, entire populations or even species may be wiped out if their habitat is disturbed by forest clearance or fires. As well, because the adults are large-bodied, slow moving, and nocturnal they are attractive and easy prey for rodents. Further threats to their survival come from collectors interested in having rare insects merely to own or to trade. Two Geodorcus species have been given legal protection but it would be desirable to apply the same protection to all the flightless stag beetles and to other flightless endemic insects as well. These unique at risk insects should have the same status as kiwi, tuatara, and other protected endemic species.
Very little is known about the biology and life histories of the New Zealand stag beetles. When we look at a stag beetle either alive and in the open or as a specimen in a cabinet it is good to ponder its life. The beetle had parents that had to find one another and a mother who could select the right substrate for the egg and larva. When fully developed the larva had to find the right place to pupate and the resulting adult may have found food and a mate. Most of these activities probably resulted from tactile and chemical processes. Systematists have a responsibility to draw attention to structures that may be sites of pheromone release or reception, for example setiferous sex patches or spectacularly developed antennal club segments of some males, on the off chance that researchers in other disciplines will be inspired to investigate them. The tufts and clusters of setae on the legs of some species of Paralissotes and Geodorcus have not been examined with a scanning electron microscope but it is likely that they are associated with pheromones which could be spread on the ground or other substrates as scent trails. Published observations on life cycles, particularly mating, oviposition sites, number of eggs laid over what period of time, and also the longevity of flightless species, would make a significant contribution towards understanding the family.
I hope the morphological section and keys will be helpful even for those with only a general entomological knowledge and that others, who may never expect to see a stag beetle, will enjoy looking at the illustrations and be able to appreciate the amazing diversity of the unique New Zealand lucanid fauna.