Smooth Stick Insect

Fast Facts

Latin name: Clitarchus hookeri

Notable feature: Green or brown with a continuous line along their thorax.

Conservation Status: Not Evaluated

Where in the UK: Only found in the Isles of Scilly. Naturalised (Originally from New Zealand). First found in the UK in 1949 at Tresco Abbey Gardens.

Smooth Stick Insect (Clitarchus hookeri) © Sid Mosdell (Flickr, CC BY 2.0)


Smooth Stick Insects are usually green or brown. They can appear similar to the Unarmed Stick Insect however, on close inspection Smooth Stick Insects can be distinguished by a line along their thorax (the middle section of their body) and pointed cerci rather than rounded cerci (a pair of small appendages at the end of the abdomen).

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 in 1949, which was also found in Tresco Abbey Gardens, and the Unarmed Stick Insect (Acanthoxyla inermis) 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.

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: 85-90mm (8.5-9cm)
      • 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 UK Smooth Stick Insect population is thought to be all-female. Stick insects in the UK share a similar annual lifecycle. 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: Adults can be found during the summer months and are mostly active at night. During the day they hide among the branches of their host trees before emerging at sunset. 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 the threats to them.
      • Fun Fact: Male Smooth Stick Insects have been recorded in their native New Zealand however, none have been found in the UK as of yet.

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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Main Image Credit: Smooth Stick Insect (Clitarchus hookeri) © Sid Mosdell (Flickr, CC BY 2.0)