Worldwide super group
Some 350,000 beetle species have been named worldwide, making them the largest group of insects. Beetles account for more than 40% of known insect species, and about 30% of all animals. Estimates suggest that as many species again – perhaps more – are yet to be discovered.
New Zealand biodiversity
New Zealand’s beetle life is diverse – there are more than 4,500 named native species. By way of comparison, this is more than all mammal species worldwide, or all New Zealand plant, fish, amphibian, reptile, bird and mammal species combined. The actual number of New Zealand beetle species is likely to be between 6,000 and 10,000.
About half of the world’s 160 or so beetle families occur in New Zealand, and most of the major families are present. Most biodiversity is within a few families – there are 11 families with over 100 species. The most diverse family is Curculionidae or weevils, with about 1,300 species – nearly one-third of the beetle fauna. This is disproportionately high – three times higher than in the UK, for example.
Other large families in New Zealand are (with approximate species numbers in brackets):
- Staphylinidae – rove beetles (800)
- Carabidae – ground beetles (420)
- Cerambycidae – longhorn beetles (180)
- Scarabaeidae – scarabs and chafers (150)
- Tenebrionidae – darkling beetles (150)
- Chrysomelidae – leaf beetles (150).
Several families are represented by only one or a few species, such as Cucujidae or bark beetles, whose sole representative, Platisus zelandicus, is confined to the remote Three Kings Islands. The Trogidae or carcass beetles have only one species in New Zealand, accidentally introduced.
Some species are widely distributed, while many are specific to certain regions. Offshore islands, such as the Three Kings, Chatham and subantarctic groups, each have a characteristic beetle fauna.
Some groups show unusual distributions. The family Chaetosomatidae was originally thought to be unique to New Zealand, until new species were discovered on Madagascar. Carrion beetles are confined to the northern hemisphere except for two New Zealand species of the genus Zeanecrophilus.
About 90% of New Zealand beetles are endemic – they are found nowhere else. Two entire families – Cyclaxyridae and Metaxinidae – are endemic. Such a high proportion of endemism is probably the result of New Zealand’s isolation, and its changing climate and geology, which has promoted the evolution of new species.
Captain Thomas Broun (1838–1919) was New Zealand’s most prolific beetle taxonomist – he described and named 3,538 new species. The quality of his work, however, did not always match his output. His descriptions were often basic, and they were rarely illustrated. Many species were described several times over – the ground beetle Megadromus meritus was given 14 different names. Controversially, Broun bequeathed his main collection to the British Museum in London.
Until the 1990s it was thought that New Zealand beetles were an ancient lineage, and had become isolated when New Zealand split and drifted away from the Gondwana supercontinent, around 85 million years ago. Others had arrived by dispersing across the ocean, or had been introduced through human activities. But research now suggests that New Zealand was largely submerged around 35 million years ago, and many plants and animals have arrived since then.
New Zealand’s beetles, like many of its plants and animals, are most closely related to species in Australia and South America.