Category: beetles

Prodontria lewisii

Critically endangered, this small, flightless, unremarkable, brown beetle has a habitat of 81 hectares in the arid Cromwell basin of Central Otago. It was never a habitat larger than 500 hectares, and the construction of the Clyde Dam and resulting Lake Dunstan combined with land repurposed for housing development and a golf course has eaten up more than 80% of their original habitat.

The remaining habitat is under threat from the ravages of the Australian Redback spider, an unwanted import who makes it’s home in the abandoned rabbit burrows that litter the sandy loam the chafer beetle lives in. The Redbacks build a web in the empty holes, and repurpose them as a nursery for baby red-back spiders. Apparently one enterprising Redback had preyed upon 70 chafer beetles, as evidenced by the midden of crispy beetle husks piled in his lair. Chafer beetles are the second favourite prey of the Redback, after the darkling beetle.

Department of Conservation staff have been gingerly removing Redbacks from the former burrows with long-handled tongs, and then infilling the holes. This seems to be an effective solution for dealing with the spider problem.

Every December a chafer beetle larvae count is carried out by DoC staff, under the brutal Central Otago sun. More than 600 soil cores are removed from the earth, and hand-sifted through by the participants, in the hope of finding the elusive little grubs. The numbers found are generally very low, maybe just a few individuals. The beetle population is estimated to be about 3000. Cromwell chafer beetle larvae spend many months buried in the sand chewing through tussock roots. They go through three phases of instar before pupating for three months. When the adult beetle finally metamorphoses, it spends it’s days burrowed up to half a metre underground, before emerging on spring and summer evenings to mate, and feast on scabweed.

I don’t know if the Cromwell chafer beetle will survive all the threats it faces. It’s difficult to feel hopeful.

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Geodorcus ithaginis

A sea stack in the Mokohinau Islands known only as ‘Stack H’ may or may not be the last remaining home for our rarest beetle. Their habitat is the size of a generous living room; they have been predated out of existence everywhere else. They are so extraordinarily rare that their home can’t be revealed as unscrupulous poachers and collecters of endangered and precious creatures could feel compelled to liberate these beetles from their remote sea stack.

They are a good-sized beetle, the males up to 32mm long, the females slightly smaller, pleasingly stocky, flightless, and a slow perambulator, which is fortunate, because there is nowhere much for them to go on Stack H. The males have a protruding mandible used for battling other males for beetle supremacy.

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Stag beetles are under threat worldwide, mainly because of habitat loss. It takes a long time to become a stag beetle; they live as larvae underground for years before briefly becoming a beetle, and require a stable habitat of rotting logs and leaf litter in order to ensure their survival. The Mokohinau stag beetles do not have the luxury of leaf litter on their stack. They live amongst the peat-like substance that forms beneath the New Zealand ice plant, in tussock plants, and under rocks. Only rugged, sea-battered pohutukawa provide fallen leaves for beetles on Stack H.

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At the start I mentioned that Stack H may not be the last remaining home for the Mokohinau stag beetle… this is not because they may have another as yet undiscovered home. Unfortunately a recent attempt at a stocktake of the beetle numbers was an abject failure. Not a single beetle was located, despite repeated fruitless searches. Quite simply, there was no evidence of the beetle to be found. There is a slim possibility that there are some as yet unmetamorphosed larvae underground, and something has befallen the adult population, but more likely they have disappeared forever, another victim of habitat loss and predation by introduced species.

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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.

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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.

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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.