There are organizations that advocate natural control of pests as opposed to the use of chemicals. One effort to control garden pests involves the use of praying mantises. While the concept is good, there are complications. In the natural world with no human intervention, there is a balance between predator and prey. When humans upset that balance, the result is always catastrophic.
In Australia, for example, rabbits were introduced to control certain plants. The rabbits had no natural enemies, and in a very short time, the rabbit population was out of control. Now there is the problem of how to get rid of the rabbits. Here in Michigan, beavers have been brought back into the river where I live. Today they have no enemies, and the beaver population has grown to the point where it is almost impossible to keep decorative trees because the beavers eat them.
The December/January issue of National Wildlife magazine (page 10) brought a new issue to our attention. People have introduced large numbers of praying mantises to control the bugs that were eating their gardens. The problem is that they not only eat bugs, but they will also kill and eat hummingbirds. Some people who have deliberately added numbers of mantises to their property have discovered that they no longer have hummingbirds, and apparently the mantises are the cause.
The Wilson Journal of Ornithology reported a study in which there were 147 cases of praying mantises catching 24 different bird species. The praying mantises capture the hummingbirds at feeders or as the birds are getting nectar from a flower. When we see bad environmental situations in nature, it is almost always due to human mismanagement and not a fault in the design of the system.
–John N. Clayton