Amazing Praying Mantis Egg Case

Discover Why Gardeners Love These Pest-Control Capsules

Egg case (ootheca) of a Chinese mantis on a plant stem
Egg case (ootheca) of a Chinese mantis.

Dendroica cerulean / Flickr (CC license)

Have you ever found a brown, polystyrene-like mass on a shrub in your garden? As the leaves begin to fall in autumn, people often find these odd-looking formations on their garden plants and wonder what they are. Many people guess that it's a cocoon of some kind. Although this is a sign of insect activity, it's not a cocoon. This foamy structure is the egg case of a praying mantis (an insect in the family Manidae).

Soon after mating, a female praying mantis deposits a mass of eggs on a twig or other suitable structure. She may lay just a few dozen eggs or as many as 400 at one time. Using special accessory glands on her abdomen, the mother mantis then covers her eggs with a frothy substance, which hardens quickly to a consistency similar to polystyrene. This egg case is called an ootheca. A single female mantis may produce several oothecae (the plural of ootheca) after mating just once.

Praying mantises typically lay their eggs in late summer or fall, and the young develop within the ootheca over the winter months. The foamy case insulates the offspring from the cold and provides them with some protection from predators. Tiny mantis nymphs hatch from their eggs while still inside the egg case.

Depending on environmental variables and the species, the nymphs may take three to six months to emerge from the ootheca. In spring or early summer, the young praying mantises make their way out of the protective foam case, hungry and ready to hunt other small invertebrates. They immediately begin to disperse in search of food.

If you find an ootheca in the fall or winter, you may be tempted to bring it indoors. Be forewarned that the warmth of your home will feel like spring to the baby mantises waiting to emerge. You probably don't want 400 miniature praying mantises running up your walls.

If you do collect an ootheca in the hope of watching it hatch, keep it in your refrigerator to simulate winter temperatures, or better yet, keep it in an unheated shed or detached garage. When spring arrives, you can place the ootheca in a terrarium or box to observe the emergence. But don't keep the young mantises confined. They emerge in hunting mode and will eat their siblings without hesitation. Let them disperse in your garden, where they will help with pest control.

It's usually possible to identify the specific species of mantid by its egg case. If you're interested in identifying an egg case you find, check out Bugguide.net, an online community of naturalists who continually share images of insects, spiders, and other related creatures they find in North America. Here you will find numerous photographs of the most common mantid oothecae found in North America. The egg case at the beginning of this article is from a Chinese mantis (Tenodera sinensis sinensis). This species is a native of China and other parts of Asia but is now well established in North America. Commercial biocontrol suppliers sell Chinese mantis egg cases to gardeners and nurseries who want to use mantises for pest control.

Sources

"Carolina Mantid Ootheca." North Carolina Museum of Natural Sciences, nationalsciences.org. Accessed 15 Sept. 2014.

Cranshaw, Whitney and Richard Redak. Bugs Rule! An Introduction to the World of Insects. Princeton University Press, 2013.

Eiseman, Charley and Noah Charney. Tracks & Sign of Insects and Other Invertebrates. Stackpole Books, 2010.

"Ootheca." Amateur Entomologists' Society, www.amentsoc.org. Accessed 15 Sept. 2014.

"Ootheca." Museums Victoria. museumsvictoria.com.au. Accessed 15 Sept. 2014.

"Praying Mantid Care Sheet." Amateur Entomologists' Society, www.amentsoc.org. Accessed 15 Sept. 2014.

"Subspecies Tenodera sinensis - Chinese Mantis." Bugguide.net. Accessed 15 Sept. 2014.