Most all of the insects found on New Zealand are found nowhere else. All earthworms, 99% of land snails/slugs, and 90% of spiders/harvestmen are endemic.
One of the most interesting insects is the Weta. This insect is often referred to as the "insect rodent", because its behavior reflects that of rodents. Wetas "hole up during the day", and come out at night. They eat vegetation and various debris found on the forest floor. They even produce "rat-like droppings"! The largest of these insects, the Giant Weta, is the heaviest insect in the world, weighing in at about 68 grams. The weta is now close to extinction largely due to predation by rats.
New Zealand is home to what is thought to be the "missing link" between segmented worm and the jointed-legged inverebrates (such as crayfish). These worm caterpillars have a segmented body (like worms), but these segments cannot be seen from the outside of the body. Each of these segments has a pair of legs and two claws. This insect has a very unique way of catching its food: it squirts slime at its prey. This slime hardens when in contact with air and falls on the unfortunate prey like a net.
All 173 native New Zealand earthworms are endemic. The Spencerilla gigantea can attain lengths of up to 1.4 meters and widths of up to 11mm.
As many species in New Zealand, the snails are thought to be some of the oldest and most primitive in the world.