This past year I have been reading a lot of papers about mantids because I will be doing my Masters thesis on the New Zealand mantis. They are very interesting animals that fill the niche of a top predator in many habitats.
New Zealand only has one native species of mantid which is called te whē/rō in te reo Māori. Te whē/rō is a name shared with the stick insect. This relates to a tradition that Māori have where, depending on which of these insect species lands on you, this will indicate which gender your child will be. Maybe New Zealanders could bring it back for some niche (and traditional) gender reveals?
The New Zealand mantis isn’t the only mantid species in New Zealand though. Since the 1970s we have had a second species in our country. Spreading from Auckland and across the North Island, the South African mantis quickly established itself in New Zealand. This South African invader is also well established in Nelson on the South Island.
These invasive mantids have caused the decline of our native mantis on the North Island. This impact is likely driven by the female South African mantis that eat our native mantis males. These males follow their noses to the exotic female only to find out that it is a dinner date, and they are on the menu.
The native mantis is more of a gentle species, where the females are unlikely to try and eat their mate. They don’t live for very long, perhaps six months in the wild. Mantids need a way to survive the winter and ootheca (little mantid egg cartons) protect their eggs while they develop. Both mantid species in NZ have ootheca, though they can easily be told apart. The South African mantis has a puffy white ootheca, which looks like a small meringue, while the New Zealand mantis has a brown ootheca that is smaller and more geometric.
Mike Bowie, and his son Matthew Bowie, looked at where the New Zealand mantis laid their ootheca. Mike recently retired after over 40 years at Lincoln University, working on many native species, including the habits of New Zealand mantids.
The Bowies found that the New Zealand mantis preferred kowhai, native broom, lancewood, and cabbage tree, which together had 78% of the oothecae. Over half of the ootheca were found on smaller branches, predominantly non-shaded. They found that these spots were warmer and brighter than other parts of the trees and this would help with development.
Oothecae were also centred on true north, which works with most New Zealand houses and fences since most properties are also facing true north. Ootheca are attached to houses and fences that face north, maximising their sunlight. This allows developing mantids to grow quickly.
The Bowies also found that there was a size difference between ootheca in Lincoln compared to those in Palmerston North. The Lincoln oothecae were significantly larger than the egg cases up north. There could be a few reasons for this and one of them is that a larger size helps them handle the colder temperatures down here. This size difference also allowed the southern population to fit a few more eggs in their ootheca giving them a bit of an advantage.
The study shows that our mantis has various adaptions that allow them to survive the New Zealand winters, especially by using the modified habitat we have created in New Zealand. Despite this, the New Zealand mantis is in decline. The South African mantis lay their ootheca in more sheltered spaces and produce oothecae that are larger than the locals, giving them advantages. They can even lay an ootheca without mating and it will hatch successfully.
Just like those male mantids, we’ll be praying for a happy ending!
This article was prepared by Master of Science postgraduate student George Gibbs as part of the ECOL608 Research Methods in Ecology course.
Bowie, M. K.; Bowie, Michael H. 2003. Where does the New Zealand praying mantis, Orthodera novaezealandiae (Colenso) (Mantodea: Mantidae), deposit its oothecae? New Zealand Entomologist 26(1): 3–5. (https://doi.org/10.1080/00779962.2003.9722103)