The May Bug, scientifically known as the common cockchafer (Melolontha melolontha), is a seasonal insect that can become a significant nuisance in gardens and lawns during late spring and early summer. These large beetles are a common sight when they emerge, often buzzing clumsily around outdoor lights at dusk. While the adults are a temporary annoyance, the true threat to your landscape comes from their underground larval stage.
Identifying May Bugs and Their Life Stages
The adult May Bug is a large beetle, typically measuring between 25 and 30 millimeters in length, with a robust, reddish-brown body and distinctive fan-like antennae. They are known for their somewhat awkward, noisy flight and their strong attraction to light sources after sunset. Adult beetles live for only about six weeks, during which time they feed on the leaves of trees and shrubs to acquire energy for reproduction.
The May Bug life cycle spans three to four years, with the majority of that time spent beneath the soil as a larva, or “white grub.” After the female lays clusters of up to 80 eggs 10 to 20 centimeters deep in the soil, the grubs hatch and begin feeding on plant roots. This larval stage is the most destructive, as the grubs voraciously consume the roots of grasses and other plants, leading to patches of brown, spongy lawn that can be easily rolled back like a carpet.
Immediate Methods for Controlling Adult Bugs
Physical removal is one of the simplest methods, most effective in the cool of the evening or early morning when the beetles are less active. Hand-pick the large beetles from affected plants or shake them off tree branches onto a sheet, then dispose of them in a bucket of soapy water.
Since adult May Bugs are strongly attracted to light, you can use this behavior against them with a simple light trap. Place a bucket of water mixed with a few drops of dish soap beneath a bright light source in the evening, as the beetles will fly toward the light and drown in the water. For foliage protection, you can apply horticultural oil or insecticidal soap sprays directly to infested leaves. These sprays act as contact killers, offering quick, localized relief, but they do not provide lasting residual protection.
Preventing Infestation Through Grub Management
The most effective long-term strategy for preventing an infestation is to target the destructive grub stage in the soil. Maintaining a healthy lawn is a strong cultural control measure, as turf with robust, deep root systems can withstand a low population of grubs without showing significant damage. Practices like proper aeration, dethatching, and avoiding excessive summer watering can help make the lawn less hospitable for egg-laying females.
A highly recommended biological control involves the application of beneficial nematodes, specifically species like Heterorhabditis bacteriophora. These microscopic roundworms are natural parasites of the grubs and are safe for people, pets, and beneficial insects. Timing is critical for nematode effectiveness; they should be applied in late summer or early fall when the grubs are young and feeding actively near the soil surface.
The nematodes require specific application conditions: the soil temperature should be between 50°F and 86°F, and they must be applied during overcast conditions or in the evening to prevent ultraviolet light from killing them. After application, the treated area must be watered thoroughly and kept moist for at least two weeks to help the nematodes move through the soil and establish themselves. For severe or persistent infestations, chemical control options are available, but these should be considered a last resort. Always follow label instructions precisely and check local regulations, as preventative measures are preferred to minimize environmental impact.