Spotting and Controlling Scarab Beetles in Your Garden

Scarab beetles are notorious tree and garden pests. They are nocturnal and cluster under light sources like streetlamps or garden and patio lights. Various species will eat tree sap, leaves and fruits of a wide variety of plants. Follow these guidelines to spot and control scarab beetles in your garden and on your trees.

Life Cycle of the Scarab Beetle

Scarab beetles lay their eggs underground. These hatch into fat white grubs, which eat organic matter in the soil. After a few weeks they mutate into pupae, then emerge as adult beetles a few days later.  

When and Where to Find Scarab Beetles

Scarab beetles are easiest to spot at the grub stage because of their thick, white, segmented bodies and large heads. Their bodies curl into a distinctive C shape at rest. They are in this larva stage for about 4 to 6 weeks from late spring to mid-summer. Adults hatch from pupae in June and July in southern Canada, and about a month earlier in the United States.

You can find the adults quickly at night, as they fly to any light source. They have large oval or nearly round bodies, in colors ranging from light green to a dark brownish-black. Check them for fan-shaped antennae, but be careful, as their pincers can deliver a painful bite. The June bug is the most common North American scarab beetle. Any beetle you see that resembles a June bug is probably a scarab beetle.

Chemical Controls

Spray a dimethoate-based insecticide on lawns and tree trunks when you spot the grubs. Spray the insecticide before dusk while the grubs and adult beetles are sleeping to prevent egg-laying. Treat your lawn or garden with this product as soon as you see grubs, because they can denude a lawn in their few weeks of life at this stage. If grubs have already infested your lawn, dig up the turf, aerate the soil, add fertilizer and replant with grass seeds before late summer.

Mechanical Controls

Lay out scarab beetle light traps around an affected tree or garden patch. The traps lure the beetles with a tiny light. The beetle pushes a roller device to unlock the box and climb in. The roller latch then locks and flips the box over, trapping the beetle inside.

Natural Predators

Magpies eat large quantities of scarab beetles and grubs when they find them.

Garden and Tree Maintenance to Prevent Scarab Beetle Infestation

Cultivate and turn over soil regularly in the garden to expose grubs to birds and other insect-eating animals. Keep garden soil healthy and moist, as beetles prefer dry soils. Pull up and control weeds. Wash plants with a mild soap to discourage beetles.

Dung Beetles

These insects are beneficial for livestock farms as they bury and eat animal dung, especially that of herbivores like cows and sheep. They do not eat anything else, so it is unlikely they will infest your garden.