Judith Tromp, of Hampden, asks :-

This animal was resting against our house in the sun in Hampden. The body was 140mm, the feelers were 90mm, and the legs approx 75-85 mm long. What is the name and what do they live on? We shifted it into a tree and it got quite aggressive.

Thomas Buckley, an entomologist at Landcare Research (Auckland), responded.

The stick insect in the picture is Argosarchus horridus.

Stick insects are among the most distinctive of our native insects yet they are also among the most poorly known. All of our 23 species are endemic to New Zealand. The stick insect Argosarchus horridus is one of our biggest insects, and certainly the longest, with a body length of up to 15 cm. Other species are not so large, being less than 4 cm long. In all the species the females are much bigger than the males.

Stick insects are famous for their stunning resemblance to foliage, which makes them very difficult to locate. This allows them remain undetected by birds, who are probably their greatest predator. Many species, particularly those of the genus Acanthoxyla, also have spines. Some species are green coloured and others are brown so as to blend in with their background foliage. When disturbed, stick insects will often fall to the ground and “play dead” for hours. Another bizarre behaviour is the “dance”, where the stick insect sways back and forwards for hours in a peculiar motion, the function of which is a mystery.

Although stick insects are sometimes active during the day, they feed mostly at night, where they can be observed by torchlight on the exterior branches of trees and shrubs.

Stick insects are common in many gardens and are frequently observed on both native and exotic shrubs. Their natural habitat includes native forest and scrub, although some species are found in high mountains, a very unusual habitat for an insect group that is largely tropical. All stick insects feed on foliage and the plant that they are found on can usually be regarded as the food source. Plants such as manuka, taraheke, ramarama, horahora and rata are popular among many of the New Zealand species.

One group of common stick insect species, Acanthoxyla, are frequently found on native podocarps such as totara and rimu. The alpine species tend to feed on plants such as alpine grasses, taraheke and pohuehue.

Many stick insects, including a number of New Zealand species breed without fertilization from males. Therefore the species consists purely of females, which lay eggs that in turn hatch into females only. Other species have both males and females or have populations in some parts of the country with exclusively females and populations in other regions with both sexes. Stick insects hatch from eggs as nymphs and go through several rounds of moulting where the skin is shed to reveal a new layer. This process allows the insect to grow because the skin itself cannot. Stick insects are most common in the summer months and many die off during the cold weather of early winter.