Females can reach up to 20 centimetres (7.9 in) (but are usually 12–15 cm), making this endemic species the longest New Zealand insect.

Males will mate with females by climbing on to their back, and using the toothed claspers near their genitalia to attach and begin copulation.

Like other stick insects, A. horridus is hemimetabolous, and nymphs grow by moulting, going through six instars until final adulthood.

[9] It can be found in gardens on ramarama (Lophomyrtus bullata) and in the wild on native and introduced Rubus species (Rosaceae) and climbing rata (Metrosideros perforata).

[3] Because of its wide distribution, range of host plants and the various habitats it is found in, A. horridus is considered an ecological generalist.