The praying mantis, with its distinctive upraised forelegs and triangular head, is often seen as a welcome garden resident and a helper in the battle against common plant pests. This large insect, belonging to the order Mantodea, has earned a reputation as a ferocious predator that keeps insect populations in check. However, the mantis’s role in a garden ecosystem is complex. The belief that they are purely beneficial requires a closer look at their indiscriminate hunting habits and the origin of the species found in most North American yards.
The Mantis as a Natural Pest Controller
The mantis is an ambush predator, relying on camouflage and stillness to capture prey. This hunting strategy makes them highly effective at catching a wide variety of insects, many of which are considered garden pests. Gardeners frequently appreciate their voracious appetite for common nuisances like aphids, flies, and mosquitoes.
Their diet also includes larger, damaging insects such as caterpillars, grasshoppers, and beetles. Mantis nymphs, the newly hatched young, begin by consuming tiny, soft-bodied insects like aphids, offering early-season control. Because they reduce pest numbers, mantises provide a natural way to manage garden health without the need for chemical pesticides.
A single mantis remains in a relatively small area, acting as a dedicated, resident hunter for the growing season. They are capable of rotating their head a full 180 degrees, giving them binocular vision and the ability to scan their surroundings for movement while remaining completely motionless. This combination of speed, vision, and patience makes them a highly efficient, though generalist, predator.
The Indiscriminate Predator: Impact on Beneficial Insects
Despite their reputation for pest control, praying mantises are generalist predators. This lack of selectivity is the primary drawback to having them in an ecosystem focused on ecological balance. They will readily consume beneficial insects, including pollinators and other natural enemies.
The mantis’s choice of prey often includes economically important pollinators like honeybees and native bees, which they frequently capture while waiting on flowering plants. Butterflies also fall victim to the mantis’s lightning-fast strike as they visit flowers for nectar. This predation on pollinators can undermine efforts to create a supportive habitat for essential garden visitors.
The mantis also preys on other beneficial insects that organic gardeners rely on for pest management, such as ladybugs, lacewings, and parasitic wasps. Consuming these natural enemies reduces the overall effectiveness of the biological control system. Furthermore, larger mantis species have been documented capturing and feeding on small vertebrates, including lizards, small frogs, and hummingbirds.
Native vs. Introduced Species
The mantis’s impact depends significantly on the species found, as many common types are not native to North America. The native Carolina Mantis (Stagmomantis carolina) is a smaller insect (two to three inches long) and has a lesser impact on larger pollinators. This species is generally less common now due to competition from introduced rivals.
The two most prevalent introduced species are the Chinese Mantis (Tenodera sinensis) and the European Mantis (Mantis religiosa). The Chinese Mantis is a much larger predator, growing up to five inches long, and its size allows it to consume a wider range of beneficial insects and small animals. The larger, non-native species are also more aggressive and actively compete with, and often prey upon, the smaller native Carolina mantis.
Gardeners often purchase mantis egg cases, or oothecae, for pest control, but these are frequently the egg cases of the non-native Chinese or European species. Introducing these larger, non-native mantises can threaten the balance of the local ecosystem by displacing native species and consuming a high number of native pollinators. To support local wildlife, it is important to identify and protect native mantis egg cases while considering the removal of non-native ones.