A Deadly Predator

September 26, 2023

Following up on last week’s blog, I have been researching and observing the praying mantis that occupies the large swaths of grasslands of Little Lake Valley. It is astounding to see the sheer number of these “deadly predators” we have flying and crawling about. They are called deadly predators because of their reputation for being indiscriminate eaters. They eat a variety of prey, from insects to reptiles to hummingbirds.

There are eight species of Mantid found in California but only four have been recorded in Mendocino County. The information was quite confusing on them and as I tried to sift through the different articles and my own entomology resource books, it got more perplexing.

The native California Praying Mantis, Stagmomantis californica, is found mostly in southern California and in the Central Valley into Colorado. I did find one reference to this species being found in northern California but nothing more to corroborate it. The other three species found in this area are the common European Mantis, Mantis religiosa, the Chinese Mantis, Tenodora sinensis, which is the largest, and the Mediterranean Mantis, Iris oratoria.

My interest was really piqued when, as I was surveying the monarch caterpillars on the milkweed plants this week, a fellow colleague and I discovered a strange sight of a dead caterpillar hanging from a leaf. As I was photographing this and looking through the lens of my camera, I saw a shocking sight; there was an upside-down praying mantis eating the monarch caterpillar as I watched. Last week I read that mantids ate monarch caterpillars by gutting them first so as not to eat the most toxic parts. This is what that strange thing was, the guts of the caterpillar hanging while the mantis ate the rest of the body. We then found another mantis on another milkweed plant where a caterpillar was calmly munching away, unaware of the deadly predator lurking nearby.

The dilemma of what to do was difficult because we did not want to interfere with natural systems of predator versus prey, although it may be that the mantis population that occupies the Willits Valley and Mitigation Lands are not native species but rather invasive.

Yesterday, I did a mantis survey with a young volunteer, and we found sixteen and a half (one was partially eaten) mantises. One of the distinguishing characteristics of the European Mantis is that they have a black bulls-eye-looking gland under their front forearms. Eleven of them had black glands under their forelegs, which made them European Praying Mantis, and five did not. This survey took about 45 minutes, and we did not have difficulty finding the mantises, they were just in the road, and one even landed on my camera!

There are 2,400 species of praying mantis all over the world in tropical and temperate climates. They have been found in fossil records over a million years old. Praying mantis are the only known invertebrates that see in three dimensions just like humans! They have two compound eyes that face forward and three simple small eyes that can detect light and motion from sixty feet away. They are active during the day since they use their sight to capture prey. They have been called an auditory cyclops because they only have one ear in the groove on their underbelly. They can only hear high-frequency sounds like the echolocation of bats that eat them. It will dive to the ground if it hears a bat. The male mantis has wings that extend past the abdomen and are active flyers. The females have larger abdomens and shorter wings so don’t fly as much. The mating season is from August to October. The female creates an egg case called an Ootheca from a foamy substance produced by a gland on her abdomen that, depending on the species, contains 10 to 100 eggs. Depending on the species again, five to twenty ootheca can be laid. This means that one praying mantis can lay more than one thousand eggs! Each egg hatches into a miniature praying mantis that can hunt insects right away.

These insects only eat live prey and have been recommended to gardeners by nurseries for the past fifty years for insect control. The only problem is that these insects are deadly predators that indiscriminately eat whatever insect, arachnid, or small creature they can get. This unfortunately includes the beneficial bugs and the pollinators. Plus, most of the time someone buys a praying mantis egg case (Ootheca) from a nursery, it is unlikely to be a native species of praying mantis. So, we are unfortunately introducing a new predator into our local ecosystems. I am now thinking about and concerned about this issue, especially after finding that European Mantis sucking the life out of the monarch caterpillar recently.