Japanese beetles, with their metallic green and copper bodies, are a common frustration for gardeners and farmers across North America. Introduced in 1916, these insects cause significant damage by skeletonizing leaves and destroying flowers across hundreds of plant species. Since bats are widely recognized as powerful natural insectivores, the question of whether they prey on the Japanese beetle is a frequent inquiry for those seeking a natural solution. This article examines the specific feeding habits of common insectivorous bats to determine their likelihood of acting as an effective control agent.
Understanding Insectivorous Bat Diets
Insectivorous bats, which comprise the majority of bat species in North America, are selective predators. Their diets are determined largely by the size, flight pattern, and texture of the available prey. While the Little Brown Bat (Myotis lucifugus) tends to be a generalist, the Big Brown Bat (Eptesicus fuscus) shows a distinct preference for beetles (order Coleoptera).
The Big Brown Bat possesses a robust skull and powerful jaws that allow it to chew through the hard, chitinous exoskeletons of beetles. This bat routinely consumes agricultural pests like scarab beetles, ground beetles, and stink bugs, confirming its capability to handle hard-bodied prey. However, soft-bodied insects, such as moths (Lepidoptera) and mosquitoes (Diptera), form a substantial part of the diet for many bat species. Prey selection often comes down to what is most abundant and easiest to catch during their nightly foraging period.
The Interaction Between Bats and Japanese Beetles
The direct answer is that while the potential exists for bats to eat Japanese beetles, the actual rate of predation is minimal. The primary reason is a fundamental biological mismatch: the Japanese beetle is a diurnal insect, active during the day, while virtually all insectivorous bats are nocturnal hunters. Japanese beetles emerge to feed and mate from late morning until late afternoon. Bats leave their roosts to forage only after sunset. This significant lack of temporal overlap means the Japanese beetle is simply not available when bats are hunting. Furthermore, while the Big Brown Bat can consume hard-shelled beetles, there is no consistent scientific evidence to suggest bats are a meaningful predator of this specific pest.
The hard exoskeleton of the Japanese beetle, which is a scarab, presents a digestive challenge, even for the Big Brown Bat. Although the bat can crush the shell, soft-bodied prey like moths provide more easily digestible nutrients and are energetically easier to process. Therefore, even if a beetle is encountered during the brief twilight period, bats often exhibit a preference for softer, more common night-flying prey. For this reason, bats cannot be relied upon to control a Japanese beetle infestation.
Using Bats as a Natural Pest Control Strategy
Although bats are not effective against the Japanese beetle, their presence in a garden or agricultural setting provides immense benefits against other damaging pests. Insectivorous bats consume vast quantities of night-flying insects, acting as a significant natural suppressor of various crop and nuisance pests. They are highly effective at controlling populations of mosquitoes and numerous species of moths, whose larvae are often destructive crop pests. Studies have shown that bats consume agricultural threats like corn earworm moths, cucumber beetles, and stink bugs, saving the U.S. agricultural industry billions of dollars annually.
Encouraging bats to roost in an area enhances the overall health of the local ecosystem, even if the Japanese beetle remains unaffected. Homeowners can attract and support local bat populations by installing bat houses in a suitable, sunny location and ensuring a nearby water source is available.