There is something captivating about large exotic insects, especially ones you can now find in your own backyard and hold in your hand. In 2022, there was an increase in the number of people reporting sightings of European praying mantis on Mayne Island. This exotic insect is a relatively new introduction to the island and appears to have increased in population in recent years. The European mantis is the only species of exotic mantis established in BC, joining our single native species, the ground mantis, which is rarely encountered and makes its home in the south Okanagan Valley. The European mantis was first introduced to eastern North America in the 1890s before being intentionally introduced to the Okanagan Valley in 1938. The first record on Vancouver Island dates back to 1999. It is unknown when it first reached Mayne Island, but the Conservancy received our first report in 2018 at the Village Bay Ferry terminal. Since then, reported sightings have increased each year.
Not a Picky Eater
The European mantis is a generalist predator, which means they are not picky eaters and will eat whatever they can catch (including each other) with their well-adapted grasping front legs. Some businesses sell these predators as a method of controlling insect pests in gardens and farms, which unfortunately causes more harm than good. The European mantis is an ineffective and counterproductive pest control method for two reasons: first, because the mantis are not selective eaters, they are unlikely to have a significant impact on whatever pest growers may hope to specifically target. Second, mantis kill and eat many beneficial insects such as pollinators and other important predators of garden pests.
It has been suggested that the cannibalistic nature of mantis puts a limit on their population density, in that as they become more numerous, they become their own predator. They are also known to be eaten by bats, birds, spiders, frogs, and snakes. Young mantis are likely eaten by a broader range of predators, some of whom may find they become the hunted as the mantis mature to full size.
European mantis live a single season, surviving winter as eggs protected in an egg mass called an ootheca. We found more than 50 egg masses last spring at Bennett Bay during our Scotch broom removal work. Each egg mass can contain up to 300 eggs. The eggs hatch all at the same time in spring, and the tiny mantis look like miniature versions of adults. Over the spring and summer they will molt approximately seven times before reaching full size. This type of insect development is called incomplete metamorphosis. Females typically reach a larger size than males and will sometimes eat the males after mating.
Exotic or Invasive?
When a species becomes established in a new place, it inevitably causes changes to that new environment. Sometimes these changes are perceived to be negative, at which time the new introduction is labeled invasive. Invasive species can cause serious problems, such as driving local species to extinction, or creating human health and economic issues. A question many are asking is: do the ecological impacts of the European mantis warrant them being labeled invasive? Because the mantis is a generalist predator, their impact is more spread out, as opposed to heavily impacting one or two species more dramatically. For that reason, their impact on the local food web is more difficult to observe. As their population increases, more specific impacts may be observed, but for now the question of invasiveness is unclear.