spiny longhorn

Spectacular Longhorns

If people are asked to think of “an animal”, they almost always name a mammal, sometimes a bird or a fish, maybe a reptile. But all of these animals are vertebrates, with backbones, and most animals, by far, are not vertebrates. There are nearly 400,000 species of beetles alone, five times as many as all the vertebrates put together.

Part of the Museum’s redeveloped exhibitions will be a display of beetles of the Whanganui area, and one of the families of beetle we will be showcasing is the longhorns.

1. Variegated longhorn

One of New Zealand’s largest and most colourful longhorn beetles, the variegated longhorn (Coptomma variegatum) larva burrows into native trees like kōwhai and tawa. It is also known as the tawa beetle. Photo: Whanganui Regional Museum.

There are almost 200 species of longhorn beetles in New Zealand, many of them large and distinctive. They are generally unmistakable, having antennae that are almost as long as their narrow bodies. The larvae of longhorns feed on wood, dead or alive, which they can digest with the help of fungus that lives in their digestive system. Longhorn larvae live for years inside branches or logs before finally emerging as an adult beetle. The adult longhorn is usually short-lived. Its only job is to mate and lay eggs.

New Zealand’s largest beetle is a longhorn, the huhu (Prionoplus reticularis). At this time of year, these large clumsy beetles often fly inside, attracted or confused by artificial lights. Huhu can give a painful nip if handled, but surprisingly they don’t eat as adults, and only live for a couple of weeks, spending all their time looking for a mate.

2.Huhu grubs

Our largest beetle is the huhu (Prionoplus reticularis). Its finger-sized grubs live for years in rotting logs, and were a valuable food, raw or cooked, for Māori. Photo: Charlotte Simmonds CC-BY.

Some species of native longhorn beetles have become pests. The lemon tree borer attacks not just native trees but fruit trees, grapes, and ornamental deciduous trees. Its larva can ringbark and kill entire branches while burrowing. The two-toothed longhorn usually tunnels into fallen logs, but is happy to inhabit firewood or stacked drying timber. It can cause real structural damage, making tunnels much larger than the tiny holes associated with furniture borer (which is in an entirely different beetle family).

3. Blosyropus spinosus

The spiny longhorn (Blosyropus spinosus) is only slightly smaller than the huhu, but is much less common. This one was found at Bushy Park. You can see the paired spines on head and thorax from which this rare flightless beetle takes its name. Photo: Tom Miles / Zoomology.

Most of our native longhorns, however, are not pests; they concentrate on breaking down and recycling rotten wood in the bush. Many are large attractive beetles, and some can even hiss or squeak when disturbed. While on a Museum moth survey at Bushy Park, we came across the rare spiny longhorn (Blosyropus spinosus), New Zealand’s second largest longhorn species. A docile flightless beetle with paired spikes on its back, it is widespread but rarely seen. The National Arthropod Collection in Auckland, with 6.5 million specimens, contained only 22 spiny longhorns from the entire country, dating back to 1915. To know this species is surviving in Bushy Park is a testimony to the intensive rat and mouse control that’s been happening there. Conservation is about more than just vertebrates.

Dr Mike Dickison is Curator of Natural History at the Whanganui Regional Museum.