Giant Prickly Stick Insect

About the giant prickly stick insect

The giant prickly stick insect, also called the spiny leaf insect, Macleay's spectre, or the Australian walking stick, is a large species of Australian stick insect. It shows striking differences between males and females. Females are heavy-bodied and covered in thornlike spikes for defense and camouflage, with long, rounded bodies that reach about 20 cm (8 in). Their wings are too small to allow flight, a condition described as brachypterous, regardless of whether a female is carrying eggs. Males are a different animal altogether: smaller and thinner at around 11 cm (4.5 in), largely without the thorny growths except around the face, but equipped with long, functional wings. Males are capable fliers and readily take to the air when disturbed or when searching for females.

Individual coloring varies widely — animals can appear brown, mottled brown, green, reddish, cream, yellowish, or entirely white. The species is endemic to Australian rainforests, with most of its range across eastern New South Wales and eastern Queensland; it has also turned up in eastern Victoria in one old record and possibly in South Australia, where it may have been introduced. A closely related and similar species, E. popa, occurs in New Guinea.

Behavior and diet

When threatened, both sexes adopt a defensive "scorpion" pose, standing on the front and middle legs while pointing the abdomen up or to the side, and folding the legs back to pinch anything that touches the abdomen — sharp rear-leg spines can puncture human skin. Adults can also make clicking sounds and release a defensive odor described as similar to toffee, and males may flash their wings open to startle a predator. Camouflage is just as central to the species' survival: it holds a curved pose while hanging inverted among foliage, with its abdomen curled over its back, and it sways back and forth or side to side when disturbed or in a breeze, mimicking the rhythm of foliage rustling in the wind — a behavior that may help it avoid detection or be misidentified as something other than prey.

Newly hatched nymphs take a completely different survival strategy: they mimic ants of the genus Leptomyrmex, with an orange head, white collar, and black body that makes them look toxic, and they move quickly to reach the trees before their locomotion slows at later molts. Females gradually gain their spiky, camouflaged adult appearance through additional molts.

The species can reproduce sexually or, when no males are present, through parthenogenesis. Fertilized eggs take about four months to hatch, while unfertilized eggs take up to nine months — in one captive case, more than 400 days — and produce only female offspring; fertilized eggs can produce both sexes and tend to yield bigger, stronger young. A female flicks her eggs away from her body with a swing of the tail, sometimes several feet, and the eggs must stay below 25 °C (77 °F) to hatch successfully. The outer coating of the eggs contains lipids and other compounds that ants treat as food: ants carry the eggs back to their nest, eat the edible outer layer, and discard the still-viable eggs in their waste piles, which incidentally works fine for captive breeders too, since removing that outer layer by hand isn't necessary for the eggs to develop.

In the wild, E. tiaratum feeds on eucalyptus, its native food plant. Captive breeders elsewhere in the world have found the insects will also eat bayberry, bramble, hawthorn, hazel, oak, photinia, raspberry, rose, and salmon berry, along with guava, although insects raised on these substitutes don't always grow as large or keep the same natural coloring as those raised on eucalyptus.

Range and habitat

The giant prickly stick insect is endemic to rainforest habitat in Australia. Most of its range sits in eastern New South Wales and eastern Queensland, with an additional old record from eastern Victoria and a possible, likely introduced, population in South Australia. Its closest relative, E. popa, is found across the water in New Guinea.

Conservation status

The giant prickly stick insect is classified as Least Concern (LC). No population threats in the wild are described here; instead, the record notes that the species is common in captivity: it's used in laboratories, kept for school projects, and popular among breeders of exotic insects across North America and Europe. Some breeders in the United Kingdom, concerned about the effects of inbreeding on captive stock, have introduced new genetic lines from abroad to keep captive populations healthy.