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Canterbury knobbled weevil

Hadramphus tuberculatus

The Canterbury knobbled weevil is the third most endangered creature in New Zealand, after Maui’s dolphin, and the Mokohinau stag beetle. They were thought to be extinct in the 1920’s, but were rediscovered by accident in 2004, alive and well, if in small numbers, in the Burkes Pass Scenic Reserve. Estimates of their numbers are between 50, and 200.

Photo credit Mike Bowie, Lincoln University.

They are 12 to 16mm in length, and heavily knobbled on their carapace, probably as an evolutionary device to avoid predation. They have been a part of New Zealand fauna for 60 million years. Regretfully, the knobbles can’t save them from the current threats to their likely extinction.

The biggest threat to the survival of the knobbled weevil is the steady decline of it’s habitat. The weevil lives exclusively on three varieties of speargrass; golden spaniard speargrass, blue speargrass, and needle-leaved speargrass. Sadly, speargrass are also increasingly rare. It’s a tough, prickly plant, which was probably repellent to the moa, so thrived prior to moa extinction, but despite being an early coloniser is now out-competed by tussocks, exotic pasture grasses, and weeds like wilding pines and lupins.

This is unfortunate, because while the adult weevils live on speargrass pollen, the weevil larvae live exclusively on the roots of the speargrass, which eventually kills the host plant. You can see how they need an endless supply of new speargrass plants in order to survive. The weevil kills the thing it needs the most… Aside from this, the weevil larvae also compete with the larvae of a number of moth species for the speargrass roots. Other threats to the speargrass host are clearance by landowners, as it is a difficult plant for stock to move through, and fire. Fire has been a problem since earliest human habitation, firstly set by the moa hunters trying to flush moa out of the forests, and then by settlers clearing forest for pasture. Speargrass is also eaten by wallabies and hares, and uprooted by feral pigs.

Weevils, like our other native insects, are also predated on by rodents, hedgehogs, feral cats, and possums. Little owls, and ruru would almost certainly eat knobbled weevils, if they could spot any. Because the speargrass itself is threatened, DOC is trialing placing cages over a small group of plants in the Burke’s Pass area where knobbled weevils are found. There are risks with translocation, because there is no guarantee translocated weevils will take to their new host speargrass plant. They have been raised in captivity with signs of breeding evident, but having an ever-decreasing gene pool is also a risk. Ultimately, the discovery of some new populations is the best hope for the survival of this species, but so far all searching has been prickly, and fruitless.

Silver brooch

 

Lasiorhynchus barbicornus.

Tuwhaipapa

The male giraffe beetle is the longest New Zealand beetle, at 85mm, the females are half that size.

They have been accused of not being a true weevil, because they lack an ‘elbow’ in their antennae, but it’s just a slur; they belong to the sub-family Brentinae.

Silver brooch

They are found commonly in the lowland forests of the North Island, though they have been found as far south as Greymouth. I am dismayed I have never seen one, as they are active during the day, and they shelter quietly in the tree canopy at night, feeding on sap. If disturbed they will drop suddenly to the leaf litter, and feign death for up to an hour, which is a long time for a beetle who only lives for two weeks, though the larvae live for a couple of years.

The sexual dimorphism is pronounced between the males and females. The males are much larger, and can fly. They have a much longer rostrum, or stiff snout, and the antennae are located at the end of it. The females are smaller, flightless, and their antennae are halfway down their rostrum, which leaves the end of their snouts free for drilling into dead tree bark in order to lay eggs.

The males use their long rostrums for fighting over females, naturally enough. If a singleton male stumbles upon a happily mating pair he will rudely rake his mandibles on the male’s back, and worse still, attempt to dislodge him by pulling on his opponents legs with his mandibles. This is probably why many males are amputees.

Once the challenger has dragged his opponent off, they will fight each other with their elongated snouts for the affections of the female. Amusingly, while this show of shirt-fronting is happening, a smaller male will often sneak in and mate with the female in question, proving diminutive size is no barrier to successful mating.

Curiously, they have been found with colonies of mites living on them. It’s unknown whether the mites are parasitising the giraffe weevils, or hitching a ride in order to disperse more widely.