Giant Spiny Stick Insect (Eurycantha Calcarata)

Eurycantha calcarata, also known as the New Guinea giant spiny stick insect (not to be confused with the giant prickly stick insect, Extatosoma tiaratum), is a large, bulky species of phasmid native to the tropical rainforests of Papua New Guinea, New Caledonia, and the Solomon Islands. Interestingly, it is one of the few phasmid species that are ground-dwelling, due to their heavier build.

Nymphs: Nymphs are ~30-40mm in length. They look markedly different from their adult counterparts, displaying a mottled green and brown colouration that gives them a moss-like appearance. Their bodies are lined with smaller spines compared to adults. As the nymphs grow, the brown colouration becomes more dominant. After 6 moults and 4-6 months, the nymphs reach maturity.

Adults: Eurycantha calcarata is a large, robust species of phasmid. Females reach lengths of approximately 120-150mm, while males are slightly smaller at about 100-120mm. The colour of adults ranges from light brown to dark chocolate brown to deep black, with an almost glossy, shiny texture. Both sexes are wingless and heavily armoured with sharp body spines, giving them a fearsome, even scary appearance.

Males are characterised by a large, curved spine on the femur of each hind leg, which points away from the body and resembles a fish hook. Intriguingly, this spine is used to make fishing hooks by indigenous people in New Guinea. Females have a prominent ovipositor, which resembles a stinger, used for laying eggs into the substrate.

Males and females live for ~12-18 months.

Eurycantha calcarata, like most phasmids, are nocturnal. During the day, they prefer to hide under cork bark at the bottom of their enclosure, often clustering together in a gregarious manner. They emerge at night to feed.

When threatened, males adopt a defensive posture by standing on their front legs and raising their abdomen and hind legs, displaying the large spine. If approached too closely, they can quickly snap their hind legs towards each other, trapping anything between them. This can pierce human skin and even cause bleeding. Due to this defensive behaviour, it is crucial to handle these insects gently. If they display an arched back and curled tail, it's best to leave them undisturbed. Females are generally more tolerant of handling.

Males also display aggressive behaviours towards one another when competing for mating rights.

Eurycantha calcarata eat a variety of plant species including bramble, hawthorn, oak, raspberry, rose, and beech, species. When selecting food plants, ensure they are free from insecticides or other harmful chemicals. Furthermore, before offering food to your phasmid, it's advisable to wash the cuttings with water to remove any surface debris and hitchhikers.

To maximise plant longevity and minimise maintenance, consider keeping the plant in a pot of water within the enclosure. However, take care to cover or reduce the size of the pot's opening to prevent the phasmids from accidentally falling in and drowning – particularly for nymphs, which are more prone to drowning.

Always provide a fresh source of food. On average, clean out the enclosure once a week, replacing old food with fresh offerings and adding new substrate to remove waste. This weekly maintenance is also an ideal time to collect any eggs that have been laid.

Eurycantha calcarata is an easy-care phasmid.

Temperature: Maintain temperatures between 20°C to 25°C during the day. It’s acceptable for temperatures to drop to ~18°C at night. This species can be comfortably kept at room temperature without issue. Note that warmer temperatures will accelerate the insects development.

Humidity: This species prefers a high level of humidity of ~70-80%, reflecting their native humid forest habitat. To maintain the appropriate humidity levels, mist the enclosure every day or every other day, focusing on the food plants rather than directly spraying the insects. This misting also provides water droplets for Eurycantha calcarata to drink – adults particularly enjoy drinking water droplets.

Adequate moisture is crucial for successful moulting, which is essential for the insect's growth and development. Use dechlorinated water for misting to prevent potential harm. A substrate of paper towels or coir (coconut fibre) can help maintain higher humidity levels.

Lighting: Mimic natural day/night cycles using either natural or artificial lighting.

When housing Eurycantha calcarata, the enclosure should adhere to the general rule for phasmids: at least 3 times the insect's body length in height and 2 times in width. A minimum size of 30cm x 30cm x 45cm (width x length x height) is recommended, though larger is preferable due to males' aggressive mating behaviour. Unlike other phasmid species, Eurycantha calcarata prefers horizontal space over vertical, but some height is still necessary for moulting.

For this species it is recommended to add bark or a flower pot at the bottom of the enclosure, providing daytime hiding spots. Cork bark is particularly well-suited for this purpose. Given their large size, branches should also be included to support the insects as they climb to their food plants at night and during moulting.

Proper ventilation is equally important as maintaining high humidity. Ensure ample airflow to prevent stagnant conditions and mould developing. At a minimum, a mesh or netted roof is recommended. Netted material also provides easier grip for the insects, which is especially beneficial during moulting.

Eurycantha calcarata reproduces sexually. Breeding is relatively straightforward, as they readily reproduce under suitable conditions once mature, provided both sexes are present. Males actively compete for mating rights, so it's recommended to maintain a female-to-male ratio of 2:1.

Females use their ovipositor to drill holes in the substrate, deposit eggs, and then cover them by sweeping substrate over the holes. A substrate container of at least 8cm depth should be provided on the enclosure floor for this purpose. The eggs are cylindrical, brown to grey in colour, and approximately 8mm in length, relatively large for phasmid eggs. They have a rough, shiny surface texture.

Eggs can be incubated in the laying substrate or removed and incubated on vermiculite or paper towels. The incubation period lasts ~6-9 months. Eggs should be kept under conditions similar to those for nymphs and adults: temperatures of 20-25°C and humidity of 60-80%. Ensure daily light exposure and regularly check for mould growth.

If you notice mould on an egg, carefully remove it from the container. You can attempt to gently wipe off the mould using a clean paper towel or soft brush. However, if the mould growth is extensive, it's best to discard the egg to protect the health of the others. If mould has developed, thoroughly clean the container housing the eggs. Pay particular attention to the substrate, especially if using paper towels. Vermiculite or coconut fibre substrates are less prone to mould growth.

In the absence of males, female Eurycantha calcarata can produce unfertilised eggs, however, this species is not parthenogenetic and so the eggs will not hatch. Fertilised eggs have a high hatch rate of ~70%.