Fatal attraction factor in decline of native mantis

A female African praying mantis lays eggs in a foamy case. PHOTO/COLIN OGLE

There's a takeover happening in the insect world - introduced African praying mantises are supplanting their native New Zealand relations.

In the Forest & Bird magazine last year writer Graeme Hill suggested killing the African interlopers and their egg cases. After 10 years of doing so he was starting to see a few of the native insects at his place, possibly as a result.

Wanganui's Lyneke Onderwater also advocates killing the African species, though she said she didn't enjoy it. She and Wanganui ecologist Colin Ogle hardly ever see native praying mantises now.

There are a total of about 2000 mantis species in the world, but only these competing two in New Zealand at the moment.

The native one is very much like an Australian species. Its most distinguishing feature is the bright blue and purple spots on the powerful spiky forelegs it uses to capture and crush insects.

It is usually a fresh green in colour, sits on top of leaves and doesn't usually survive the winter.

Females lay a sculptural egg case before winter, from which about 20 tiny insects emerge in spring. They initially feed on small insects like aphids and fruit flies. They move up to large insects such as cicadas and wasps as they increase in size.

Female New Zealand native mantises, Orthodera novaezealandiae, can fly and they rarely eat their males after mating.

The African praying mantis, Miomantis caffra, was first noticed in the Auckland suburb of New Lynn in 1978, online dictionary Wikipedia says.

It's very common and spreading. Some have been seen as far south as Christchurch, Mr Hill said.

It's often larger than the New Zealand species, and is green to pale brown in colour. The front part of its body is thinner than that of the New Zealand species and it has no blue and purple spots on its forelegs.

Females can be especially large and sometimes survive the winter. They can't fly and often eat males during or after mating.

Their takeover may be speeded by the fact that native mantis males mate with them and then get eaten.

All mantises eat a lot of other insects - as many as 25 flies each a day, according to Andrew Crowe's Which New Zealand Insect.