There are masters of camouflage making themselves at home in some of the groves of oak trees in Manitoba. Finding them can be tough, because they can be hard to tell from a twig. While stick insects generally inhabit tropical forests, we do have one species that occurs in Manitoba. So stick with this month’s Incredible Creatures, and we will explore the fascinating world of the northern walkingstick, as well as look at some of the incredible sizes and adaptations of some tropical species.
Masters of disguise
Stick insects, sometimes known as walkingsticks, make up an order (called Phasmatodea) of about 2,500 species. The scientific name for this group of insects comes from the Ancient Greek word phasma, meaning an apparition or phantom. This refers to the resemblance of many species to sticks or leaves (making them not easy to see).
The one species of stick insect we have in Manitoba is the northern walkingstick (Diapheromera femorata). They are not common, but can be found in and around oak trees. They usually feed at night. Often when hiking I would check or tap the leaves of an oak tree to see if I could find a walkingstick, but with no success. But this past July, while collecting and observing some insects with the Miami Junior Gardening Club, one of the members found 3 walkingsticks under some oak trees. What a thrill to see.
Males and females of the northern walkingstick differ slightly in appearance. Females are slightly bigger and get to about 9.5 cm, while adult males average about 7.5 cm. Males are brown, whereas females have a hint of green to their brown colour. Nymphs (the young stages before they become adults) are green and only become a brownish colour when they reach maturity. Nymphs become adults during the summer and fall. Females of the northern walkingstick drop eggs singly on to the forest floor. Eggs overwinter in leaf litter and hatch in the spring. There are some interesting features of the eggs that protect them from predators and parasites, sometimes with the help of ants. Stick insect eggs in general resemble the seeds of plants. The eggs of the northern walkingstick resemble the seeds of legumes. The eggs additionally contain a tasty area called a capitulum, which makes them quite attractive to ants. The capitulum on an insect egg mimics a similar tasty and nutritious area called an elaiosome on plant seeds that depends on ants for distribution. Ants will take the eggs into their nest, thinking they are a seed. They eat the capitulum, but this does not damage the interior of the egg. The egg is then discarded at the bottom of their nest. This will provide protection for the eggs. When the tiny (a few millimeters long) walkingsticks hatch, they are allowed to exit the ant hill. Seed dispersal by ants is called myrmecochory, and plants and animals that enjoy a partnership with ants are called myrmecophiles.
Some birds, such as crows and American robins, will feed on northern walkingsticks. Northern walkingsticks have an amazing ability to regenerate legs that are lost from attack by predators. When attacked by a predator, the legs may separate from the body (this is called autotomy). Some species have the ability to regenerate lost legs at the next molt. But only the nymphs can do this (adults do not molt). These are the only insects able to regenerate body parts.
Hiding in plain sight
Walkingsticks are world-class hiders that use camouflage and mimicry. In addition to their physical appearance, walkingsticks use “behavioral camouflage”. During the day they extend their front and rear legs to the fore and aft of their body and can remain motionless for hours. This ability would be the envy of every mime. If they feel threatened by a predator, or insect enthusiast, they may sway back and forth like branches in a breeze. As they search for leaves they may also sway slowly back and forth, mimicking the movement of a branch in the wind.
Walkingsticks are terrestrial (living on land). If you see a similar critter in the water, it’s an unrelated insect called a water scorpion. Not to worry though, in spite of the name they can not sting you like a scorpion.
And now, for some amazing facts about some of the tropical walkingsticks. Walkingsticks are the longest insects in the world. A species from Borneo called Chans megastick (Phobaeticus chani) can get to 56.7 centimetres (22.3 in) in total length, including the outstretched legs. That is nearly the length of 2 rulers placed back-to-back. It was long regarded as the longest insect in the world. But in 2016, a new species from China called Phryganistria chinensis (there is no common name for it yet) was measured at 62.4 cm. So there is a new record holder. Stick insects can be incredibly long. And new species of stick insect continue to be discovered. Just this year descriptions of 4 new species from Peru and Ecuador, and two new species from Vietnam have been published. Some lucky biologist may yet discover a new species that breaks the record for length.
Interesting, bloody, and gross forms of protection
Stick insects have incredibly diverse ways of protecting themselves. Some stick insects have cylindrical stick-like shapes, but others have flattened, leaflike shapes. The body of some has further modifications to resemble vegetation, with ridges resembling leaf veins, bark-like tubercles, and other forms of camouflage. A few species, such as the Indian stick insect (Carausius morosus), are even able to change their colour to match their surroundings.
Some species, such as the giant prickly stick insect (Extatosoma tiaratum), have been observed to curl the abdomen upwards over the body and head to mimic scorpions. Females of this species are covered with thorn-like spikes, and can get up to 20 cm long. Newly hatched nymphs of this species are ant mimics, resembling the insects in whose nest they are born.
Some species are equipped with a pair of glands at the front edge of the thorax (middle part of an insects body) that enables the insect to release defensive secretions, including chemicals that produce distinct odors, and others that cause a stinging, burning sensation in the eyes and mouth of a predator. The defensive chemicals from one species is used as a treatment for skin infections by a tribe in Papua New Guinea because of its antibacterial constituents. Some species can bleed reflexively through the joints of their legs and the seams of the exoskeleton when bothered, allowing the blood (hemolymph), which contains distasteful chemicals, to discourage predators. Another ploy is to regurgitate their stomach contents when harassed, repelling potential predators.
Aside from being the longest insects in the world, stick insects have some interesting behaviours and ways of protecting themselves. Next time you are near some oak trees, watch for the incredibly interesting northern walkingstick. You may have to look closely though. Those “stick-like” things swaying in the breeze may not be what they seem. But stick to it and you may see one.
Incredible Creatures is a monthly contribution to provide information on some of the common yet often not well known creatures that we share space with in Manitoba and abroad.