In January this year the Museum helped run a night-spotting Whanganui Summer Programme field trip to Bushy Park. The participants were lucky enough to see, up-close, two long skinny insects that had been found by DOC’s Scotty Moore under a rotten log. They were giraffe weevils, New Zealand’s longest beetle.
The giraffe weevil’s Latin name, Lasiorhynchus barbicornis, means “hairy-nose with a bearded horn”. Its Māori name is pepeke nguturoa, or long-beaked beetle. (By the way, nguturoa is another Māori name for kiwi). They’re also called tūwhaipapa, after the god of newly-made waka, because their nose resembles a canoe prow. All these names refer to the male, who has a snout as long as the rest of his body with a fringe of hairs underneath.
Male and female giraffe weevils look very different, and were named as two different species when the specimens collected by Sir Joseph Banks on Captain James Cook’s first voyage were studied back in Europe. Female giraffe weevils are tiny compared to males, and have a shorter snout which they use to drill an egg-laying hole into dead trees. Their eggs hatch into grubs which eat fungus inside rotting wood for two years, finally pupating and digging their way out of the tree as adult weevils in summer. Peak emergence time is February, so right now is your best opportunity to see adult giraffe weevils in the wild, as they only live for a few weeks before mating and dying.
An adult male giraffe weevil’s primary concern is finding a female, and they use their enormously long noses to fight other males by biting and wrestling, trying to dislodge their opponents from the tree trunk. When they find a mate they literally stand over her while she lays an egg, driving off all challengers. Some much smaller males employ a different reproductive strategy: while the big macho males are distracted by fighting and posturing, these little males will sneak in and mate with the female under their rival’s enormous nose. Research by biologist Chrissie Painting at Auckland University revealed that both these tactics were roughly equally successful at fathering offspring, which is why we see such a range of body sizes in male giraffe weevils. It’s like a field experiment in evolution: if one strategy were more successful, natural selection would favour it, and eventually male giraffe weevils would have all evolved a similar body size.
Chrissie was able to find several dying karaka trees in Matuku Reserve near Auckland where she could watch males battle and sneak, and observe their life cycle. She used tiny dots of coloured nail polish to mark the different males so she could tell them apart, and filmed them tossing each other off trees. Giraffe weevils are a useful study animal for observing evolution in action, because they’re active in the daytime (unlike many beetles) and easy to observe. After having to work long nights studying native harvestmen, she describes the weevils as “little angels”.
If you want to see real-life giraffe weevils for yourself, you could venture into lowland native bush between October and March, look on the trunks of rotten trees, and, if you’re lucky, see two long-nosed insects jousting.
Dr Mike Dickison is Curator of Natural History at Whanganui Regional Museum.