Finding a mate
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.
Who needs males?
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.
Keeping stick insects
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.