Conservation Matters: The biggest weevil of all in New Zealand

A large female giraffe weevil (top) and its smaller male mate. Photo / File

New Zealand is proudly home to the world's largest brentid weevil. The endemic giraffe weevil is our longest beetle, males measuring 80-90mm, of which half is their snout, or rostrum. Females are smaller, 45-50mm long, with a shorter rostrum.

The rostrum has a comb of stiff short bristles underneath. At the end of the snout are the antennae, which branch off at the tip of the rostrum in the male but half way along the rostrum in the female.

The males use these for fighting off rival males at mating, but the female's shorter rostrum is designed to protect the antennae as she prepares a site for her egg.

They have an elongated head with red-brown markings on their elytra (hardened forewings, folded over their back to protect their delicate hind wings). When they fly the elytra are raised and the hind wings are unfolded. Giraffe weevils are the only weevil in the world to have a scutellum, a triangular plate on their thorax.

Giraffe weevils are found in native forests in both the North and South islands, and their body size increases and rostrum length decreases the further south they live.

They are much more common in the North Island. Adults are most likely to be seen in spring, around the lower trunks of trees such as lacebark, pigeonwood, rewarewa, tawa, pukatea, rimu, and especially karaka and mahoe.

These diurnal insects feed on sap, and if disturbed will throw themselves backwards into the leaf litter, where they play dead for up to an hour.

Adults only live a few weeks over October-March, with peak numbers in February, and a sex ratio of 60:40 in favour of males. Mating occurs over these months, the female chewing a 45-degree hole in a tree 0.5mm wide by 4mm deep.

She must remove her jaws from the hole every 0.5mm to clear the hole and her mandibles, and while she is distracted by amorous male, which stands over her, guarding her as she chews and helping her extract her rostrum from the tree if she gets stuck.

These diurnal insects feed on sap, and if disturbed will throw themselves backwards into the leaf litter, where they play dead for up to an hour.

Once the hole is big enough the female lays a single egg deep into the cavity and blocks up the entrance with sawdust and bark.

Females can mate several times before laying, so fighting males are common. They try to drag their mandibles along their opponent's back or grab one of their legs. This then leads to grappling, as they try to push each other off the tree with their rostra.

Often a sneaky smaller male makes the most of the distracted fighting males and mates.
Larvae can live up to two years, feeding on fungi inside the larval tunnels. While pupating their long rostrum is tucked underneath them and unfolds as the adult emerges. These guys are seriously cute.