Explore the winter garden and you might find a brown foamy case attached to a twig, stem or fence post. These are Mantis ootheca and they contain hundreds of young.

Mantids are ferocious

Mantids are an ancient and ferocious predator. Still and green as a bean pod, their large eyes follow you. Their raptorial legs bristle with thorns, poised motionless in the air. They pre-date T. Rex in the fossil record. Mantids know what they’re doing. When another insect stops to drink from a flower or nibble a leaf, they strike like lightning, piercing their prey with their thorny arms. Their muscular legs are powerful enough to kill a hummingbird and mantids have been observed eating the larvae of monarch butterflies. Here’s how they do it:

While doing unrelated experiments in a local field, Jamie Rafter from the University of Rhode Island noticed that mantises would gut monarch caterpillars before eating them. It’s not a delicate process. After grabbing a victim, the mantis starts nibbling at it, chews open a hole, and lets the guts fall away. Around 40 percent of the caterpillar goes to waste.

This isn’t typical behavior for the mantis. Rafter showed that when they captured the non-toxic caterpillars of the greater wax moth or the European corn borer moth, they ate everything, guts and all. They only left 14 percent of these meals, and even then, only because bits of blood would messily dribble away when they ate.

National Geographic “Chinese Mantis Guts Its Toxic Caterpillar Prey” JANUARY 25, 2013

Are Mantids beneficial?

I have mixed feelings about Mantids. Unfortunately, those we encounter in Michigan are almost certainly non-native. The European mantis (Mantis religiosa) was introduced accidentally in New York in 1899, and the Chinese mantis (Tenodera aridifolia) was introduced near Philadelphia around the same time.

Historic records show there many have once been a native species in Michigan, the Carolina mantis (Stagmomantis carolina). It is only 2″ long compared to the 4″-6″ size of the introduced mantids. It may have disappeared as it was outcompeted, and it may have always been rare in these parts as we are on the northern edge of its range. However, recent iNaturalist observations have found the Carolina mantis in Detroit and Washtenaw County, plus some in Toledo, Fort Wayne, and Chicago. It may be that they are extending their range to include Michigan again as the climate warms.

Mantids are widely considered a beneficial garden predator, but they are simply a predator, devouring anything they can catch – bees and butterflies, tree frogs, hummingbirds and spiders. Mantids will eat anything that moves. While these large and fierce predators are fascinating to watch, are they a healthy part of the ecological balance in a native Michigan garden? Do we remove their crunchy brown cases as a non-native species or leave them be?

To learn more about preying mantises, check out Praying Mantises of the United States and Canada, and share your observations on iNaturalist.

The Carolina mantis egg case is long and flattened.
photo: Beatriz Moisset, CC BY-SA 4.0, via Wikimedia Commons
A Chinese mantis egg case is thicker, more square.
Photo: © Hans Hillewaert via Wikimedia Commons

Thanks to George Hammond and Mike Kielb for contributing to this post.

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