Giant Weta

It is one of the very heaviest, and the single heaviest insect ever reliably weighed is a giant weta — a captive, egg-swollen female Little Barrier giant weta that tipped the scale at around 71 grams, more than a small bird. In normal condition giant wetas weigh less, in the 20-to-40-gram range, which still puts them among the bulkiest insects alongside the Goliath beetle, the elephant beetle, and the largest stick insects. "Heaviest" depends on how you measure — Goliath beetle larvae may out-mass an adult weta, and the record is sensitive to whether a female is carrying eggs. But a large, gravid Deinacrida is the usual answer to "the heaviest insect."

New Zealand split away from other land masses about 80 million years ago and evolved in near-total isolation with no native land mammals except a few bats. Ecological roles that mice, rats, shrews, and hedgehogs fill elsewhere — nocturnal ground-level browsing, seed and litter processing, being prey for owls and reptiles — were instead taken up by insects, birds, and reptiles. Wetas, an old lineage of flightless cricket relatives, expanded into the "invertebrate mouse" niche and, freed from mammalian predators and competitors, some lineages evolved to a very large size. The giant wetas are the extreme result. The same isolation produced the flightless kiwi, the kakapo, and the moa.

Not really. A giant weta has powerful-looking jaws and long spiny legs, and a large one handled roughly can give a scratch with its hind claws or a weak nip, but it has no venom, no sting, and jaws built for chewing leaves rather than cutting flesh. Its defensive display — rearing back, throwing its spiny hind legs up over its body, and hissing by rasping a leg against pegs on its abdomen — looks alarming but is a bluff. Wetas are slow, docile, and easily handled by researchers, and they pose no threat to people. The bigger concern is handling them gently enough not to hurt the insect.

Because almost everything about them makes them easy prey for introduced mammals. They are large, flightless, slow-moving, ground- or shrub-dwelling, and active at night at exactly the times rats, mice, stoats, and hedgehogs forage. Ship rats and kiore reached New Zealand with human settlers and Polynesian and European voyagers, and giant wetas vanished from the mainland and from any island the rats colonised. Today most surviving populations are confined to rat-free offshore islands or intensively managed, predator-fenced mainland sanctuaries, and conservation involves eradicating rodents from islands and translocating wetas to establish new safe populations.