Peter Kwiatkowski of Dunedin asks :-
I found a stick insect, with a body length of 9.5cm, on a house wall. Is this one fully grown or do they get bigger?
Anthony Harris, a zoologist at the Otago Museum, responded.
From the photograph you supplied that is a very large Acanthoxlya geisovii.
A geisovii normally has a body length of 8.9-9.2 cm. This species is moderately large, stout (for a stick insect!), bright green (it can also be brown), with many shining black spines, the intersegmental margins yellow, the bases of all femora dark red, the antennae grey and banded with black. Large spines occur on the head, thorax and legs.
This species is represented only by females, which reproduce by parthenogenesis. No male has ever been found of this or any of the eight species of the genus Acanthoxyla.
A geisovii is common throughout New Zealand. It has been introduced into England, where, among other localities, it is found in Tresco Abbey Gardens on brambles and on the tree Cupressus sempervirens.
A geisovii is dwarfed by Argosarchus horridus, New Zealand's largest stick insect, whose females grow to 15 cm long. These impressive giants are not uncommon in suburban Dunedin, but are seldom seen on vegetation. When they walk onto the walls of a house, they are at once noticed and the Museum is frequently called. Male horridus are much smaller than females.
The 23 species of stick insects known from New Zealand are all flightless, long and thin, and are native. They eat leaves of shrubs and trees and are sometimes found on roses and conifers in gardens. They are harmless.