Starting in the early 1900s, praying Mantis were released in North America to control pests. The practice continues. If you Google “praying mantis Canada,” the first two responses are big box stores selling mantid egg cases.
Mantis are voracious predators. They will devour anything they catch—and that’s why they are not an ideal biological agent. Although, they might catch the caterpillar eating your cabbage, they might instead take down a bumblebee that is innocently pollinating your crops or attack an assassin bug that preys upon pests.
In the unnatural backyard environment where hummingbirds sip on sugar water from red plastic containers and Mantis are bought to either control pests or entertain kids, something ugly is happening. Mantis are hunting hummingbirds. The evidence is on video and in pictures (again, go to Google if you enjoy seeing ugly images of bird-insect predation).
The unsettling pictures can be interpreted as a sign of best-laid plans gone awry. Mantis don’t pose a threat to hummingbird populations as a whole but this is a dramatic example of how humans can’t predict the impact of biological introductions. A more troublesome (but less dramatic) example is the introduction of the Asian ladybeetle (ladybug) which has displaced native species of ladybeetles which are more effect predators in the garden and less of a pest in our houses.
Biological pest control in the garden and fields is a great way to control pests without chemicals – but providing habitat for native insects and birds is more effective than releasing imported species.
Source: Bird Predation By Praying Mantises: A Global Perspective: Martin Nyffeler, Michael R. Maxwell, and J. V. Remsen, Jr. The Wilson Journal of Ornithology. Vol: 129, No. 2, pp: 331-344. 2017.
- Janet Wallace