In fact there are now five species at large in the UK with the vast majority for now being in Devon and Cornwall.
Stick insects are interesting creatures best known for their exceptional camouflage. They eat the leaves of fairly common plants such as privet and bramble. It is thought that all the individuals found in the UK are females but these can lay fertile eggs without the need for a male, a process known as parthenogenesis. Adult females live for only a few months, they die off each winter but by that stage will have laid eggs from which the next generation of stick insects will hatch in the following spring. Like other insects, stick insects grow by shedding their skin. From spring through to early autumn they gradually increase in size making September the best month to find them.
The ‘unarmed stick insect’ is the commonest species accounting for about two thirds of all records. It was first identified at a garden nursery in Truro, Cornwall, in the 1920s where it was shipped from New Zealand on the plants which were destined for the large gardens of Cornwall and Ireland. This stick insect is now found across Cornwall (including the Isles of Scilly), in Plymouth (Devon) and in south west Ireland. In Cornwall the best spots remain around Truro and in the well established gardens around Falmouth and the River Helford.
The unarmed stick insect (photograph shows a young unarmed stick insect) typically grows up to 10cm long, and has quite a smooth body which can be green or brown. Adults have a dark line along the back of the pronotum (between the head and body) which helps identify this species.
The ‘prickly stick insect’, also from New Zealand, is found in Cornwall (including the Isles of Scilly) and Devon. The first record of this species in the UK was in Devon in 1909 and it was found on Tresco, Scilly, in 1943. Individuals from Tresco were deliberately released into a garden in St Mawes, Cornwall, in around 1959 and from there it has spread. It is similar in size and colour to the unarmed stick insect but can be easily identified by the small black spines all over its body.
Finally there is the ‘laboratory stick insect’ (also known as the ‘Indian’ or ‘Common Green’ stick insect) which is kept commonly as a pet in the UK. Individuals are occasionally released so it is sometimes spotted in the summer or autumn but apparently it cannot survive the British winter.
Outside of the south west of England the laboratory stick insect is probably the most likely to be encountered but since the spread of the other species has been relatively swift, aided by our continued movement of plants around the country and beyond, it is worth looking out for all stick insect species anywhere in the UK.