Stick insects belong to the insect order Phasmatodea – the name comes from the Greek word ‘phasm’, meaning phantom. The order includes about 3,000 species worldwide, with most diversity around the tropics. New Zealand’s temperate climate supports more than 20 described species of stick insect.
Stick insects look and behave like twigs or leaves to avoid being eaten. Also known as walking sticks, they come in a wide range of colours, textures and sizes, although they are all well disguised in their natural habitat. Their main predators are birds that hunt by sight. As a result of natural selection, and pressure from birds and other hunters, stick insects have evolved a suite of extraordinary features, structures and behaviours.
During the day most stick insects sit where they are least visible. Although some eat, they generally remain still, move very slowly, or sway like leaves in the wind. At dusk and at night they are more active, seeking out their preferred leaves to eat. Adults of the small spiny stick insect (genus Micrarchus) often move down to the base of the ribbonwood trees they feed on. They hide among the fallen twigs and leaves, while green nymphs of this species stay among the foliage.
New Zealand’s largest stick insect, Argosarchus horridus, often settles where there are fewest leaves but lots of twigs in the trees it feeds on. Females can be up to 20 centimetres long. Adults of the all-female variable stick insect (genus Acanthoxyla) lie along twigs where foliage is most dense. Species of the alpine genus Niveaphasma live among the tangled branches of Muehlenbeckia species.
In 1991 a new stick insect species (Asteliaphasma naomi) was found near Lake Waikaremoana. The single female specimen is held at the Museum of New Zealand Te Papa Tongarewa in Wellington. Further searches around the lake have only found another similar species (Asteliaphasma jucunda). Is the insect kept at Te Papa a strange variant of that species? Or do others of her kind live around Waikaremoana?
Different stick insect species prefer particular plants. The bristly stick insect (Argosarchus horridus) eats ramarama and ribbonwood. Niveaphasma eat Muehlenbeckia. Stick insects of the genus Clitarchus eat kānuka and mānuka. Endemic stick insects (those unique to New Zealand) will eat a range of plants, either native (pōhutukawa, rātā) or not (blackberry, raspberry). Acanthoxyla stick insects eat a range of native plants, but are unusually fond of the exotic macrocarpa and cedar trees commonly found in urban areas.
There is scattered information on the status of and knowledge about stick insects in Māori tradition. Names include rō, whe and wairaka. In some traditions they were considered to be relatives of the mantis. If either of these landed on a woman it signified she was pregnant, and which insect it was indicated the child’s sex. Some sayings claim that gardens are unsuitable where there are stick insects. In other sayings, when they drop onto you from a forest tree it is a sign that you have entered a sacred site.
In legend, before creating people, the god Tāne Mahuta fathered (with Punga) the trees, birds and insects of the forest. It was Tāne who pushed apart the sky (Ranginui) and earth (Papatūānuku) so there was light, allowing the forest inhabitants to see, breath and move. The insects are considered to be the children or embodiment of Tāne and deserving of respect.
In the story of Rātā, who cut down a tree to build a canoe without first paying respect to Tāne, the insects gathered each chip of wood and leaf and returned them to their proper place so the tree was whole again.
One problem about looking like a stick is that it makes it hard to find other members of your species. As with most multi-cellular organisms (eukaryotes), stick insect reproduction usually requires two individuals. Living throughout the forest canopy and understorey, and unable to use visual signals, stick insects find mates by smell. Like many insects, they release chemicals (pheromones) recognised only by other members of their species.
The life cycle of New Zealand stick insects takes between one and two years.
During copulation, male and female bodies are joined for several days, and the much-smaller male rides around on the back of the larger female. One possible reason for the male’s diminutive size is to avoid being seen and eaten – a single stick moving in the wind is not unusual, but two sticks moving together might catch a hungry bird’s eye. After copulation, females produce fertile eggs with no further need for the male.
When their eggs are ready, most of New Zealand’s endemic stick insects simply drop them. As adults are mostly in the forest canopy, the eggs fall to the ground. When stick insects are abundant, falling eggs striking tree leaves sound a little like rain. On the ground the eggs are small and hidden among leaf litter. After three months to a year, tiny, long-legged nymphs emerge from the egg.
No males of the stick insect genus Acanthoxyla have ever been found – every Acanthoxyla has only a mother. Each species is a matrilineage, where all reproductive effort produces females who do not need mates. This may in part explain the success of these insects, which are common and widespread. Wild populations also live in cedar trees in southern Britain – almost certainly the result of eggs being accidentally carried in the soil of New Zealand plants exported to Britain.
Some stick insects produce fertile eggs without mating. Animals that reproduce without males are described as parthenogenetic. In New Zealand, most species have males and females, although in some cases the females can make eggs with or without mating (e.g. Clitarchus). The exception is the genus Acanthoxyla, which has no males.
Some stick insects are widespread in forest and scrub (genera Acanthoxyla, Argosarchus, Clitarchus, Techtarchus and Micrarchus). Spinotechtrachus and Asteliaphasma genera are restricted to the northern North Island, including Coromandel, East Cape and Northland, and are rare. Niveaphasma are only known from the South Island, where they occur most often in the subalpine zone, but also in Dunedin.
The most commonly encountered species in New Zealand gardens are the variable stick insect (Acanthoxyla species) and common stick insect (Clitarchus hookeri). But in some areas, including Wellington’s suburbs, it is not unusual to find these and species of Tectarchus, Argosarchus and Micrarchus living close together.
Stick insects can be kept in captivity if they are cared for. They need good ventilation – a box with one side made of mesh (for air movement) is ideal. Many species will eat blackberry or pōhutukawa leaves. Fresh leaves should be supplied weekly. The box should be kept outside, under cover on the shady side of the house. Direct sun could heat the cage too much and kill the insects. In dry weather the insects and leaves should be sprayed with a water mister every few days.
Salmon, John T. The stick insects of New Zealand. Auckland: Reed, 1991.
Trewick, Steve, and Mary Morgan-Richards. Stick insects. Auckland: Reed, 2005.