Tiny mantids emerge
Early this spring, I found three Chinese mantid egg cases on dried stalks of plants that had been knocked to the ground by fierce winds we’d been having. I rescued the cases and the stalks they were attached to, sticking them in a pot holding a dipladenia. A few weeks later, I enjoyed watching the mantid nymphs inside them emerge.
Mantids, in the insect family Mantidae, have enlarged, barbed forelegs that evolved to catch and grip prey. Stealth predators, the mantids lie in wait for prey, upright and with forelegs folded, which led to their being called “praying mantises.” As fierce predators that can take on even the occasional hummingbird, perhaps “preying mantis” would be more apt, although only species within the genus Mantis can rightly be called “mantis.”
The two largest mantids in our area, the Chinese mantid
(Tenodera sinensis) and the European mantis (Mantis
religiose), were introduced into North America decades ago to control garden pests. The Chinese mantid, at four inches long, is larger than the European species, which is three inches long. Both are bright green and both, especially the Chinese mantid, are often kept as pets or used in classrooms for educational purposes.
Native mantids are only found in southern North
America, with the Carolina mantid (Stagmomantis carolina) the most common one in our area. It can easily be differentiated from the two introduced species by its smaller size (two inches) and dusty-brown color.
In late summer, the female Chinese mantid lays eggs encased in a frothy case, called an ootheca, that soon hardens into a protective shell that looks like brown Styrofoam. Its ootheca is squarish, while those of the other two mantids are more oblong. Once the female deposits the eggs in the ootheca, they begin hatching into nymphs. As temperatures fall, their development stops, restarting in early spring as temperatures rise again. Once sufficiently developed, the nymphs exit the ootheca through tiny holes that had formed as the case hardened.
Having serendipitously come out onto my deck as the first ootheca erupted with nymphs, I grabbed my camera to try to capture the event. The nymphs wriggling out of the egg case were wingless and a bit more than a quarter-inch long. Their still-limp legs were folded against their bodies as they emerged but soon hardened, at which point the young mantids could walk and quickly began to disperse. Over the next few days, whenever I could take a break from work, I visited the little mantids to monitor their behavior and take more photos (see a slideshow online at rappnews.com/wildideas).
While female mantids are notorious for eating males while they’re mating with them, research indicates this happens only about 25-30 percent of the time. And rather than sexual cannibalism, a behavior common to some other species as well, this seems to be more about opportunism. The female, which is larger than the male, is more likely to eat the male when she is hungry and the hapless male is the only food nearby. Also contrary to common wisdom, males do not willingly sacrifice themselves for the chance to mate. Instead, they approach females cautiously and, if caught, will fight back.
If the male is not cautious, he can literally lose his head over the female but can continue to mate with her even after she decapitates him. While through this process, he does contribute to his offspring’s survival through feeding the female, but he is also probably helping the offspring of other males. Adult Chinese mantids live only a few months, and they make the most of it — breeding throughout the summer with various mates, with all the female’s resulting eggs going into the one ootheca she produces.
Mantid nymphs are also known to eat their siblings, but this again appears to be more indiscriminate hunting by hungry mantids rather than purposeful cannibalism. While fierce predators, newly emerged nymphs are limited in what they can safely prey upon because of their size. They mostly rely on fruit flies and other tiny insects in that first instar (life stage). They can go through up to seven instars before getting their wings and becoming adults, which occurs in late summer.
I personally saw no sign of the nymphs trying to eat each other; instead, they seemed to avoid face-toface contact with their siblings. The bulk of the first brood ran to the top of the stalk the ootheca was attached to. Most of these lined up on either side of the stalk, facing downward with forelegs in the classic “praying” position, looking like an army ready for battle.
Over a few days, almost all nymphs in the first brood dispersed, just as more emerged the second ootheca. None have emerged from the third egg case, which perhaps had been laid in an earlier year and was now empty. One day, I noticed lots of spider silk in the pot with the oothecas and of another plant nearby, although I couldn’t find any more spiders. The next day, all the nymphs had disappeared. They probably dispersed on their own, but spiders or other predators might have raided the brood the night before.
Out of the 100 eggs, on average, the Chinese mantid female produces in the few months she lives after becoming an adult, only a few of the nymphs that hatch out are likely to survive. The others succumb to larger predators, from spiders to reptiles and birds, or to harsh weather. Still, enough survive to make this Asian insect hugely successful in colonizing North America. As the foliage dropped off plants around my yard last fall, dozens of other oothecas attached to stems were revealed.
This was the first time I’d watched an ootheca hatch out since I was child, when I’d put one in a jar for that purpose. This time I knew more about the process, losing only a bit of my childish wonder as I watched this drama unfold.