This Bug Is Big as a Gerbil. Fortunately It Loves Carrots

"What's up, Doc?" asked no giant weta ever. That noise is trademarked.

You know that scene in the newish King Kong where those folks get eaten alive in a pit of giant insects? It’s a damn character assassination, through and through. The huge cricket-like bugs among them are based on the giant weta, the heaviest reliably reported insect on Earth, at 2.5 ounces. And really, the movie bugs could have been even bigger for all I care—it’s that their crummy attitude is all wrong. Giant weta, for their monstrous size, are actually quite sweet. Not like cuddly sweet, though you’re welcome to try, but sweet nonetheless. They demand an apology. Or else…they’ll…just kinda just sit there and eat carrots.

Weta are New Zealand’s most iconic bugs, around 70 known species that range from the big ones like the giant weta to other smaller varieties: the “tree,” “tusked,” “ground,” and “cave” weta, all equally excellent in their own unique ways. They all differ in size and features, but all are products of the strange evolutionary history of New Zealand, an island that’s enjoyed relative isolation. That is, until humans arrived and started making a mess of things.

If the weta look to you like crickets addicted to protein shakes, you’re not far off. They are indeed in the same family, but in their long isolation in New Zealand, the weta have gotten weird. None can fly, for instance, because there have historically been no terrestrial mammals here. “That’s the critical part,” says biologist Priscilla Wehi of New Zealand’s Landcare Research, who you can see below calmly acting as a tree weta’s chew toy. “What that meant was that, as with a lot of our birds, being flighted wasn’t so important.”

You see, while flight may seem to be pretty legit, it’s energetically costly, and nature abhors a waste of energy. Without mammals chasing them around, weta have been able to stick to the ground to save energy. The same happened to New Zealand’s kakapo, the only flightless parrot in the world, a odd-looking bird that climbs trees to look for food and sort of just plummets out of them.

In part, it’s flightlessness that has allowed the giant weta to grow to such an extraordinary size. But there are limits to such growth, and the weta may well be pushing them. This is because insects don’t breathe like humans do. Instead of lungs, they have holes in their exoskeleton that open to tubes branching through the insect’s body, providing every cell with oxygen. This all works well and good, but it limits the insect’s size, since only so much oxygen can get deep in the critter as it dissolves into tissues.

But some 300 million to 400 million years ago, when oxygen levels were bonkers (35 percent of the atmosphere compared to 21 percent today), bugs grew huge—like dragonflies the size of seagulls and millipedes over 6 feet long—because more oxygen meant the gas could diffuse deeper into their huge bodies. Scientists think the oxygen plummeted to current levels when a giant space maid vacuumed it out (though it probably had more to do with a drop in sea level and drying out of land masses), so these days insects are a more reasonable size.

Not So Giant, But Definitely More Bitey

The other varieties of weta may be dwarfed by the giant type, but they’re no less extraordinary. The male tree weta, for instance, is equipped with gigantic mandibles, which it uses to battle other males for the right to mate, building harems of up to eight females. “They sometimes inflict damage on each other,” says Wehi, “which can even result in the loss of a leg or some other bit of their body, and they might try to throw the other male weta from the tree.”

The impressive jaws of the tree weta.

But there’s an alternative to battle. If the environment for whatever reason doesn’t produce enough food for all the tree weta, as some males molt they’ll stop growing, putting them at a severe disadvantage in battle. “So you might be more of what we call a sneaker, where because of your small size, you would wait until there’s a large male guarding a big harem of females and he was otherwise occupied fighting somebody else. And then you might be trying to mate with the females when he wasn’t looking.” (This clever little trick happens elsewhere in nature. Cuttlefish males change their body posture and coloration to mimic a female, then sneak right under the oblivious male’s belly. Thus he passes down genes not for brawn, but for smarts.)

There’s also the tusked weta, which like the tree weta fights for females, only its weapons do indeed look a bit like elephant tusks. And down in the undergrowth lives another type, the aptly named ground weta. This one digs burrows and waits there for other insects to traipse by, then pounces. Still another has adapted to life in caves, packing extra-long antennae it uses to feel around in the darkness.

All species have brilliantly adapted to life in island isolation. And accordingly, many are in trouble.

Mammalian Massacre

Humans arrived in New Zealand in the 13th century, but they didn’t arrive alone. Stowed away was the Pacific rat, which found a bounty of tasty creatures that had evolved there in total absence of mammals (save for bats). Fast forward to the 19th century, when Europeans brought the rest of the mammals that would lay waste to New Zealand’s endemic wildlife: cats, stoats, other types of rats. Now half of the island’s native bird species are gone.

A weta would never do the can-can, because that’s trademarked too. It would, however, lift up its spiny leg in order to ward off predators.

As for the weta, the tree variety seems to be doing alright. It takes shelter in small holes in trees, largely out of reach of marauding rats and such. But what’s really suffered is the lumbering giant weta. “They’ve been absolutely smashed by rats,” says Wehi. “So there have been huge conservation efforts in New Zealand, where we’ve used offshore islands as places where we can create habitats or place animals that are really badly affected by these introduced predators.”

A rather more ambitious approach is to build sanctuaries on the mainland. Crews have fenced off an entire mountain and trapped out all of its mammalian predators. Endemic species normally ravaged by mammals were then introduced to live with fewer hassles, just like they used to. Weirder still, a small population of giant weta has survived on a farm in a patch of a nasty prickly plant called gorse. The thicket, it seems, is impenetrable for rats—not to mention human researchers. “So you can probably imagine the poor people who have to go in and try to count their population,” Wehi says.

Read more at Science Daily