I saw this object in my community garden plot about a month ago. I didn’t know what it was so I placed it in a protected spot in a flowerbed. Today, I bought it home to study. I remember seeing one in the garden plot last year. My guess was that it was some sort of insect egg case.
Nature Mystery: Whose Egg Case?
I put this object under my stereomicroscope and peered at it through my illuminated hand lens. The texture of the object is crisp and crunchy-looking. If you have ever seen and chewed fried porks rinds then can imagine what this looks like. I see tiny holes where tiny creatures have exited or entered. There is also a large hole on the back, right side. The rear segments have the coverings worn away. There are deep chambers in the object.
According to my Tracks and Signs of Insects book, this is the ootheca (egg case) of the European Mantis (Mantis religiosa) called the ‘Praying Mantis”. Did you know that the Praying Mantis is an introduced species? There are 20 species of mantises north of Mexico and I know that at least three are non-indigenous. The three I know of are called European, Chinese, and Mediterranean mantises.
The ootheca is the scientific name for the egg cases of cockroaches or mantises. The ootheca is made of frothy material that is a secretion of the accessory glands of the mother’s body. The female shapes the ootheca as she is depositing it. The frothy material hardens into a many-chambered case. If you spot one of these oothecae, a small white thread of silk may hand down from the central ridge. The young used this thread to climb down from the ootheca.
The case protects the eggs from drying out or being eaten. The mother mantis attaches the ootheca to plant stems, walls, rocks or other hard surfaces. The eggs will overwinter in the ootheca and the nymphs will emerge in the spring. Up to 100 or more tiny mantises will emerge from the ootheca. The mother dies soon after laying the eggs. The young mantises will go through gradual metamorphosis. The young mantises look like tiny adults. They will molt between six and nine times before becoming adults.
Are Mantises Good for the Garden?
I think this was promoted by people who didn’t truly understand how mantises operate. Or just wanted to sell more dubious nonsense to gardeners.
Mantises are large insects with large forearms. With their large claws, mantises can’t grasp tiny insects that plague garden plants. Aphids, small beetles (looking at you Colorado Potato Beetle!), mites or scales aren’t on the mantis menu.
Mantises need larger prey. So, they hang out at flowers and eat anything they can manage to catch and get into their mouths. They eat bees, wasps, and other desirable species. In short, their main food consists of pollinators. The adult mantises aren’t giving gardener’s much help.
And yet again, the garden industry promotes releasing mantis eggs into their gardens as a form of pest control. This is how the Chinese (Tendera aridifolia), European (Mantis religiosa), and Mediterranean (Iris oratoria) mantises were introduced into North American ecosystems. The European Mantis goes by the name “Praying Mantis”. Releasing mantises as biological pest control is not recommended.
Questions Raised about the European Mantises
As I learned about the European mantises lifestyle, I wondered how the introduced mantises have contributed to the demise of indigenous pollinators. Indigenous bees, wasps, flies are the main sources of mantis diets. Have introduced mantises displaced indigenous mantises? Do mantises also eat insects that eat those pesky aphids, mites, and other garden pests? How does an introduced mantis affect the ecosystems in our gardens?