Acanthoxyla prasina

Prickly stick insect
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Phasmatodea
Family:	Phasmatidae
Genus:	Acanthoxyla
Species:	A. prasina
Binomial name
Acanthoxyla prasina (Westwood, 1859)
Synonyms
Acanthoderus prasinus Westwood, 1859 Acanthoxyla speciosa Salmon, 1955

Acanthoxyla prasina, the prickly stick insect, is a stick insect in the order Phasmatodea and the family Phasmatidae.^[1] It is native throughout New Zealand, although it is less frequently reported than "common" stick insect species. It has been introduced to Britain, predominantly Cornwall and Devon, and to the south-west region of the Republic of Ireland.^[2][3] It has a thorny skin, which is used as camouflage.^[4]

Acanthoxyla prasina is a large insect; their body length ranges from 7.5 to 11 cm long when fully grown as adults.^[5] Their bodies tend to be wider than other stick insect species. They come in two different colour forms: green and brown in various shades. There are eight subspecies, some of which have prominent dark spines on the top of the thorax and abdomen.^[6] Acanthoxyla prasina have various number and size of their spines (prickles) including one characteristic spine on the underside of their abdomen, at the base of their subgenital plate.^[6] Acanthoxyla prasina has black spines across the top of individuals of A. prasina heads, mesothorax, metathorax, abdomen and femora.^[6] Their antennae are on average just slightly longer than the fore femora and the tail on the end of their abdomen is shorter and more circular than that of other subspecies.^[6] Camouflage, body structures and behaviors help A. prasina avoid predation.^[7]

Acanthoxyla prasina has no male individuals; A. prasina are exclusively females. They reproduce through asexual reproduction called parthenogenesis.^[8] Prickly stick insects lay eggs that are 4.2 mm long and 1.8 mm high.^[5] Their eggs are brown/grey, oval shaped and are covered in small spines. Female stick insects lay their eggs on the ground, and they begin to hatch in spring when the weather warms.^[9] Each individual will lay hundreds of eggs in its lifetime but all the eggs that are laid have a 99% mortality rate.^[3]

Hatchlings emerge as nymphs. At one day old they are approximately 2 cm long.^[5] Ananthoxyla prasina will moult approximately 5–6 times in roughly 6 months before reaching adult size.^[10] They usually moult at night. Once emerged, they will likely eat their old skin. Insects in the genus Acanthoxyla live for 12–24 months.^[9]

Acanthoxyla prasina can be found throughout New Zealand, where it was originally endemic.^[11]

Ananthoxyla prasina was accidentally introduced to Paignton, UK, in 1910,^[12] although other sources describe them as Acanthoxyla subspecies, not Acanthoxyla prasina,^[3] or as the smooth stick insect Clitarchus hookeri.^[13]

No male had ever been seen within the species or genus Acanthoxyla until 2016 when one was discovered in Cornwall.^[13] This single male was the result of a rare mutation. It is unknown if the male was capable of producing sperm or inseminating females because the specimen was killed, dried and added to the collection at the Natural History Museum in London.^[14]

Acanthoxyla prasina are forage feeders.^[8] These stick insects feed on a variety of native plants, as well as some introduced species coniferous trees; radiata pine, macrocarpa, cypress and common garden plants.^[6] Acanthoxyla prasina are nocturnal; they usually feed at night.^[8]

Birds are the most common predator of A. prasina. Many native and introduced species feed on A. parsina, including house sparrows, blackbirds, silvereyes, chaffinches and yellowhammers.^[9]

Much of the knowledge and wisdom from the tangata whenua of New Zealand about stick insects has been scattered or lost.^[6][7] Stick insects were considered to be relatives of mantids and were called rō, whe and wairaka.^[6] Different tribes had their own stories and beliefs involving insects. If a stick insect or mantis crawled onto a woman, it indicated she was pregnant and the type of insect was an indicator of the child's sex.^[6] When a mantis or stick insect fell onto a human in a forest, the area became a sacred site.^[6] Māori believed the presence of a stick insect would indicate that the land would not make a good garden.^[6] There is also the Māori legend of Tāne, who is considered the creator of insects.^[7]

The entire Acanthoxyla genus likely evolved by hybridization. This hybrid origin theory is highly likely as the genus contains both diploid and triploid lineages. ^[6][15] The genus Acanthoxyla may have risen from Clitarchus hookeri through two or more hybridizations.^[16] The maternal species could be Pseudoclitarchus sentus or an extinct sexual Acanthoxyla.^[16] It has been observed that Acanthoxyla genus has low genetic diversity, suggesting poor differentiation.^[16]

• List of stick insects of New Zealand

Wikimedia Commons has media related to Acanthoxyla prasina.

• Acanthoxyla prasina discussed on RNZ Critter of the Week, 17 September 2021