By Fern Campbell
Most people are able to identify praying mantids in our landscapes and think of them as a cool beneficial insect, a “guardian against pests.” But a closer look reveals a more complicated picture. Both native mantids and non-native invasive mantids inhabit our landscape and can have a significant impact on pollinators and the ecosystems they support.
Many refer to a member of this insect group as “praying mantis” but mantis refers to the specific genus, while the term mantid refers to a larger group of insects that appear to be praying when at rest. This creature looks quite tranquil, sitting quietly with its praying pose, forelegs upraised, camouflaged, waiting for some unsuspecting insect or other small animal to wander by. The mantid’s neck allows the head to rotate 180 degrees to scan the area. When the insect wanders by, the praying mantid quickly snags a meal, using the long spines on the upper insides of its forelegs to hold its prey. Mantids do kill harmful plant-eating pests, but as generalist, ambush predators, they also kill virtually everything else, including beneficial insects. “They just eat whatever is moving and within their reach,” said Michael Maxwell, a behavioral ecologist at National University in La Jolla, California.
Identifying Invasive Mantids
The Chinese mantis (Tenodera sinensis) and the European mantis (Mantis religiosa) are the two most prevalent invasive species of mantids found in Virginia and the eastern United States. The Chinese mantid is believed to have been accidentally introduced to the U.S. in 1896 on a shipment of plants to Pennsylvania. In the 1930s, European mantid egg cases were purposely sold for garden pest control and as a biological control agent for the spongy moth, then called the gypsy moth, in the eastern U.S.
After developing adult wings, the Chinese mantid can reach five inches long. Its brown or green coloration provides effective camouflage, and its wings extend the entire length of its abdomen. The European mantid is about three to four inches long and is usually greener in color than the Chinese mantid. Like many invasive species, their aggressive nature poses a threat to the native Carolina mantis (Stagmomantis carolina), which is more brown than green in color and much smaller at two inches long. Its wings cover only two-thirds of the abdomen. The larger invasive species outcompete the Carolina mantis for food and will even eat the Carolina mantis. Thus, the smaller, native Carolina mantid (Stagmomantis carolina) is seen much less frequently and is relatively uncommon.
The Impact of Mantids
Scientific studies have demonstrated some of the effects of mantids on pollinators and their habitat. In a study published in 2014, Michael Maxwell found that the largest single component of the diet of the native mantid Stagmomantis limbata was honeybees, a species in decline. Maxwell and his colleagues have also documented 147 cases of praying mantids catching birds, mostly hummingbirds, which are pollinators. Maxwell noted that the mantises often sit on flowers waiting to kill insects and other prey.
Chinese mantids are so large and abundant they consume a large number of beneficial pollinators and other native species including small birds, reptiles and amphibians as well as the smaller native Carolina mantis. Erin E. Wilson Rankin and colleagues found that “Overall, both T. sinensis and M. religiosa fed on a diversity of diet items in old fields. Mantids preyed upon species that filled a variety of ecological roles, with the majority (>75%) of their diet being herbivores, predators and pollinators regardless of whether mantids were included as prey.”
The horticulture team at the Brooklyn Bridge Park in New York made similar findings, noting that the large Chinese mantids indiscriminately consume large numbers of beneficial insects, such as bumblebees, flower flies, butterflies, and other pollinators. This 85-acre public waterfront park is managed as wildlife habitat with primarily native plants, using organic techniques and encouraging biodiversity through research and experimentation. The Brooklyn team observed numerous large mantids on flowering plants in summer and fall and often found a pile of discarded monarch butterfly wings on the ground below. They also reported that the larger the mantid, the larger the prey they will eat. And of course, the more mantids there are, the more prey they consume. Concluding that predation pressure from mantids was becoming a significant threat to many of the insects attracted to the park, the Brooklyn team has begun to mitigate the problem by selectively removing and destroying the egg cases – called ootheca – of the non-native mantids.
Help Control Invasive Mantids
Destroying the egg cases (“ootheca”) of the Chinese and European species before they hatch can help keep populations in check. Because the egg cases are formed in late summer/early fall, scout your landscape in winter to find the egg cases. They can be attached to a variety of woody shrubs, herbaceous plant stems, twigs or even fence posts. Freezing winter temperatures kill any remaining adults but the egg cases provide protection. Mantid nymphs emerge when temperatures again reach approximately 70° in the spring.
Control depends on identifying which egg cases (ootheca) belong to invasive mantids. The female covers her eggs with a foamy substance that hardens into a texture similar to Styrofoam. Depending on the species, the egg case contains hundreds of eggs. The photo guide below can help with identifying invasive versus native mantid egg cases. The ootheca of the Chinese mantis, most commonly sighted, is puffy, round to cube shape with a foamy texture. It is ping-pong ball size and straw brown in color. The ootheca of the native Carolina mantis is elongated and slender. It is relatively smooth and has a sequence of lighter and darker brown stripes. Both the European mantis and the Carolina mantis ootheca have a similar elongated shape, but the European mantis egg case is not as flattened or as smooth in texture. The major difference is the color of the egg cases. The European mantis ootheca is solid pale brown with no striping while the Carolina mantis is greyer in color with a white midrib. The egg masses of the nonnative mantids can be crushed or cut open and submerged in water, tied up in a garbage bag or better yet, fed to chickens.
Protect Native Mantids
If you find the ootheca of the native Carolina mantis, do not disturb the egg masses. Although they are generalist predators, they are small in size and have less of an impact than the invasive mantids.
Don’t Buy the Invasive Mantids
Garden and pet stores continue to aid in the spread of the invasive species by marketing them as a form of garden pest control. Encouraging the population growth of these invasive species can be detrimental to our native Carolina mantis, as well as to our overall pollinator populations. Don’t buy invasive mantids. Let’s give our native species the opportunity to thrive without added competition.
As North Carolina Extension Agent, Debbie Roos states, “Getting rid of the predominant invasive Chinese and European mantids egg cases annually will hopefully help reduce predation pressure and help maintain a better balance of species. It doesn’t make sense for us to create habitat for pollinators and other beneficial insects, only to let the invasive generalist predators feasting unchecked on the critters the habitat has attracted.” By controlling the nonnative mantids and by supporting our region’s only native mantid, we will maintain the balance she advocates and better manage our landscapes for biodiversity. Gardeners can think of this as “weeding insects” in much the same way we weed unwanted plants.
Featured Photo: Carolina mantid, Kansas Department of Agriculture, Bugwood.org
This article was reprinted from the February 2024 issue of The Garden Shed, Piedmont Master Gardeners monthly online newsletter. Find more fascinating science-based articles on a wide range of horticultural topics HERE.
SOURCES and additional reading:
“Bird Predation By Praying Mantises: A Global Perspective,” (Nyffeler, Martin, Maxwell, Michael R., and Remsen, J. V., The Wilson Journal of Ornithology, 129(2) : 331-344), bioone.org/journals/the-wilson-journal-of-ornithology/pdf.
“Challenging the Conventional Wisdom About Praying Mantids,” Debbie Roos, North Carolina State Extension.
“Diets of two non-native praying mantids (Tendera sinensis and Mantis religiosa) consumption of arthropds across all ecological roles”, Erin E. Wilson Rankin, et. al, Science Direct, 2023.
“Get to know your local mantis,” University of Maryland Extension.
“Managing Pollinator Habitat: Reducing Invasive Mantids at Brooklyn Bridge Park,” Bella Ciabattoni and Pawel Pieluszynski.
“Praying Mantids,” Gary Watkins and Ric Bessin, Student and Extension Specialist.
“The Invasive Mantis Species,” Brandywine Conservancy.
