Praying mantis are striking looking insects. Adults can grow to about the length of one of your fingers and they have a tiny, triangular-shaped rotating head at the end of a long, slender body. Praying mantis can be hard to see unless they are moving thanks to their green colouring and their ability to stay very still as they hunt. They are less well-known for their assistance to gardeners than ladybugs and hoverflies but they are almost as effective at eating eggs, larvae and mature adults of a range of garden pests. Hungry young praying mantis nymphs ravenously eat aphids and the eggs of caterpillars. Adults are known as general predators – meaning they may well eat a ladybug one minute and a cabbage white caterpillar the next. So there is a bit of give-and-take with these cool looking creatures. They are still well-worth encouraging as they are one of the only predators that feed on moths at night before they can lay eggs on plants that will then be stripped by their caterpillars. Adults also eat shield - or stink - bugs, flies, mosquitoes and cockroaches.
In autumn, adult females lay rows of eggs in a stubby white casing – about the thickness of a pencil. These can often be seen on the branches of shrubs as well as tucked into the corner of walls and splits or cracks in timber. Eggs hatch in spring and tiny, hungry nymphs appear ready to take on juicy aphids.
There are two species of praying mantis found in our gardens. Native praying mantis (see photo above) is always bright green, with a long straight neck and blue spots on the inside of its forelegs. This native species is being pushed out by a naturalized South African praying mantis that is recognizable by its narrower neck and colour range from light green to brown and an absence of blue spots on its forelegs.
Our native praying mantis creates an egg case that has a row of small open holes along it whereas the South African produces a closed egg case. If you want to reduce the threat to native praying mantis then removing these closed egg cases when you see them is probably the best way of going about it.
Avoid using chemical pest controls as they can wipe out an entire generation of praying mantis adults and nymphs that can take a long time to re-establish. Pests however will re-populate your garden far more quickly and you’ll have no allies around to help out. Biological pest control is all about patience, when the pests turn up the predators will not be far off.
If you are pruning trees and shrubs or doing an early winter garden tidy up keep an eye out for the egg cases. If you find them on prunings then separate the stems they are attached to and re-locate in your garden. Make sure the egg casings are not left lying on the ground or the ants will make quick work of them.