Unarmed Stick Insect

Fast Facts

Latin name: Acanthoxyla inermis

Notable feature: It’s the longest of all Stick-insects found in the UK.

Conservation Status: Not Evaluated

Where in the UK: Truro, Cornwall. Naturalised (Originally from New Zealand). The Unarmed Stick-insect (Acanthoxyla inermis) was recorded at Truro, Cornwall, in 1979. Subsequently it was found that it had been established in Treseder’s Truro nursery since the 1920s, only 100 metres from the 1979 record.

Unarmed Stick Insect (Acanthoxyla inermis) © Malcolm Lee


The Unarmed Stick Insect is green or brown and can appear similar to the Smooth Stick Insect on first glance. They can camouflage themselves well due to their stick like appearance and appendages.

There are no native stick insects in the UK, however, three species from New Zealand, have become naturalised in the UK over the last 100 years, and almost all are in southwest England. This means that they live and reproduce here in the UK in the wild. The Prickly Stick Insect (Acanthoxyla geisovii) was the first to be discovered in 1909 and was followed by the Smooth Stick Insect (Clitarchus hookeri) in 1949, which was also found in Tresco Abbey Gardens, and the Unarmed Stick Insect which was recorded at Truro, Cornwall, in 1979.

The stick insects came to be here in the UK, thousands of kilometres from their native lands in New Zealand when plants, including Tree Ferns, from New Zealand were shipped to nurseries in southwest England. In the Eucalyptus forests where the plants came from, stick insects live high in the canopy. Their eggs rain down on the forest floor, and many will be caught in the crown and the rough ‘bark’ of the Tree Ferns, to be transferred with the other plants to the UK. As stick insects can reproduce parthenogenetically a single egg arriving in the UK can lead to a viable colony. The UK population was thought to be all female until a male was found in England in 2018.

Unlike some ‘non-native species’, the stick insect species currently found in the UK appear to have self-sustaining populations and are thought to have no negative impact upon native wildlife or plants. Although further research is needed, they can be considered naturalised in the UK and are an exotic addition to the gardens and green spaces of southwest England.

      • Size: 90-105mm (9-10.5cm)
      • Life span: After hatching in the spring, stick insects will become mature by mid-summer with the adults typically living only three or four months. Few survive into the winter.
      • Diet: Herbivorous
      • Reproduction: The Unarmed Stick Insect shares a similar annual lifecycle with the other stick insects in the UK. They breed parthenogenetically – meaning that the young hatch from eggs produced without fertilization by a male – laying several hundred eggs in summer and early autumn. These are simply dropped onto the ground below where the insect is feeding. They hatch out the following spring as miniature adults, some 12mm long, and climb up the first stem they meet. Nymphs grow quickly by shedding their skins five or six times to become mature in mid-summer. Adults typically live only three or four months, with few surviving into the winter.
      • When to see: They can be seen from April to December. As the insects are surrounded by food (such as bramble and privet), and have no need to find a mate, they have little natural inclination to move far. Only in the autumn, when the leaves fall off the plant, will they wander to seek food or warmth. As the weather turns colder, stick insects venture out onto south-facing walls to bask in the sun. This enables them to maintain their body temperature – and makes them easy to spot! Most of the stick insects will die off in the first autumn frosts, but some individuals will survive the winter and thus small colonies have developed.
      • Population Trend: Not evaluated.
      • Threats: Not enough is known about stick insects to understand threats about them.
      • Fun Fact: The Unarmed Stick Insect keeps itself camouflaged by swaying and moving with the breeze like the rest of the plant it is on.

How you can help:

Find out more about naturalised British stick insects from the Phasmid Study Group. If you find a stick insect in the wild, please record your sighting via the Phasmid Study Group Reporting Page.

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