Wetas are a unique group of about 100 insect species found exclusively in New Zealand, making them endemic to the island nation. They are ancient, flightless members of the Orthoptera order, which also includes grasshoppers and crickets. This group of insects represents one of New Zealand’s most distinctive examples of evolutionary isolation. Their lineage traces back millions of years. Geographic confinement allowed them to evolve into a diverse array of forms, filling ecological niches that elsewhere would be occupied by small mammals. The name “weta” comes from the Māori language.
Defining Physical Characteristics
Wetas are generally recognized for their robust, armored bodies and impressive size compared to most other insects. Some species are among the heaviest insects in the world; a large female giant weta (Deinacrida) carrying eggs can weigh up to 70 grams, which is heavier than a sparrow. The body structure is typically heavily sclerotized, providing a tough, protective exoskeleton. They possess very long, slender antennae, which often exceed the length of their body. All wetas possess powerful mandibles, or jaws, used for feeding and defense. The most distinctive feature is their enlarged hind legs, covered in prominent, sharp spines, which are held ready for a defensive posture. New Zealand wetas are all wingless, a trait common among the island’s invertebrates.
A Diversity of Species and Habitats
The term “weta” is an umbrella classification for a wide range of species that have specialized into five distinct ecological groups. This evolutionary radiation was possible due to the long-term absence of terrestrial mammalian predators in New Zealand. Each group occupies a different niche, showcasing the biodiversity within this single insect lineage.
Giant Weta
The Giant Weta (Deinacrida) is the largest group, known for island gigantism, with some reaching body lengths of up to 100 mm. These eleven species are primarily herbivorous and are now mostly restricted to offshore islands or high-altitude mainland areas where introduced predators are absent.
Tree Weta
The Tree Weta (Hemideina) is the most common group, with seven species found in native forests and urban gardens across the country. They are arboreal, living in holes or tunnels, known as galleries, in tree trunks.
Cave Weta
Cave Wetas (tokoriro) are not closely related to the other weta groups, belonging to a different family (Rhaphidophoridae). There are around 60 species, characterized by extremely long antennae and slender legs, allowing them to navigate dark, subterranean environments. These species lack hearing organs, relying instead on specialized hairs and pads to sense ground and air vibrations.
Ground Weta
Ground Wetas (Hemiandrus and Anderus) are a diverse group of about 30 species that typically hide in burrows in the soil during the day.
Tusked Weta
The relatively rare Tusked Weta (Motuweta and Anisoura) are distinguished by the prominent, curved tusks that protrude from the mandibles of the males. These specialized jaws are used in ritualized combat between males, often over territory.
Remarkable Survival Adaptations
Wetas have developed a range of biological and behavioral mechanisms to thrive in their varied New Zealand environments. Most species are strictly nocturnal, emerging from their daytime shelters after dark to forage. Their diet is generally omnivorous, consisting of foliage, fruit, flowers, and smaller invertebrates, allowing them to be flexible consumers.
When threatened, many weta species adopt a defensive posture, raising their spiked hind legs over their bodies. They may also use stridulation, where they rub pegs on their hind legs against ridges on their abdomen to produce a rasping, hissing sound intended to deter a potential predator. The powerful mandibles are also used for biting as a last line of defense.
A specialized survival mechanism is exhibited by the Alpine Weta, which survives freezing temperatures through cryoprotection. These insects produce high concentrations of glycerol and other sugars in their body fluids, acting as an antifreeze to prevent fatal ice crystal formation within their cells. This adaptation allows the weta to tolerate having up to 82% of its body water frozen solid, enabling them to survive winter in the harsh, high-altitude scree slopes of the South Island.