May/June beetles

What is may/june beetles?

May/June beetles, also called June bugs, are a large group of scarab beetles in the genus Phyllophaga. More than 200 species live in North America. The adults are the heavy reddish-brown beetles that thump against screens on late-spring nights. Their grubs, sometimes called true white grubs, are bigger than Japanese beetle or chafer grubs and have strong jaws.

Unlike most lawn grubs, these take two to three years to finish growing. Most of the damage comes in the grub's second year, when it is large and feeding hard in spring and summer. Because one brood often outnumbers the others, an area may see a big adult flight about every third year. Damage to lawns shows up as yellow, wilted, loosely rooted patches, and animals often dig up the turf to get at the grubs.

UW-Madison says control is rarely worth it unless an area has a history of damage. A heavy grub year does not mean you need to treat every year, because the next generation may be small.

Signs and damage

• Discolored, loosely rooted patches of lawn in mid to late summer that look like drought stress: yellowing, wilting and stunting.
• Skunks, raccoons, turkeys or birds digging up turf to eat the large grubs.
• Big reddish-brown beetles banging into lit windows and screens after dark in late May and early June.
• Now and then, chewed leaves on oaks and other trees near lawns, usually minor and local.

May/June beetles identification: what to look for

• Adult: Robust beetle 1/2 to 1 inch long, reddish-brown to nearly black. Long slender legs, flattened front legs for digging, and layered fan-like antenna tips.
• Larva: Fleshy C-shaped white grub with a reddish-brown head, three pairs of legs and strong jaws, up to 1 1/4 inches. The raster is a zipper-like row of spines.
• Eggs: Laid in clusters in the soil in May and June; some species prefer sod-forming grass for egg laying.
• Timing: Adults fly at dusk in late May and early June. Grubs do the most harm in their second spring and summer.
• Damage: Grubs prune roots so turf yellows, wilts and loosens; adults occasionally chew leaves of oaks and other trees.

Life cycle

Most species take three years, though two- and four-year cycles occur; in Wisconsin, P. tristis takes two years. Adults emerge in late May and early June once soils warm, feed on tree leaves at dusk, and females lay eggs in the soil. In year one, grubs feed on organic matter and roots and move deeper for winter. In year two they come back up in spring and do the most damage, molting to the third stage by midsummer. In year three they feed less, pupate by late summer, and the new adults stay in the soil until the next spring (University of Minnesota, UW-Madison, Purdue).

When to look: Watch for adults at lights in late May and early June. Look for grub damage in lawns from spring through mid to late summer, especially the spring and summer after a big beetle flight.

May/June beetles look-alikes

A few things get mixed up with it:

• European chafer (Amphimallon majale): Adults are smaller (about 1/2 inch) and lighter tan, and they swarm around trees at dusk in June and early July. Grubs mature in one year.
• Northern masked chafer (Cyclocephala borealis): Adults are smaller and yellow-brown with a dark band across the head. Grubs are about 1 inch and mature in one year.
• Japanese beetle (Popillia japonica): Grubs are smaller (about 1 inch) with a V-shaped spine patch. Adults are metallic green and feed in daylight.
• Green June beetle (Cotinis nitida): Adults are green and fly in daylight. Grubs are about 2 inches, very wide, and do not curl into a tight C.

How to control may/june beetles

Cultural control

• Keep plants and turf healthy with proper watering and feeding so roots can tolerate some grub feeding (UW-Madison).
• Know your local damage history and watch for big adult flights; both are better guides than treating by habit.
• Sample before acting: cut one-square-foot pieces of sod in a few spots and count grubs.
• Have grubs identified (your county Extension office can help) since Japanese beetle grubs look similar but follow a different calendar.

Biological control

• Birds eat the adults, and spiders, mites, predatory beetles, wasps and flies attack the grubs, including the pelecinid wasp Pelecinus polyturator (University of Minnesota).
• Natural diseases, including a Cordyceps fungus and milky disease bacteria, also infect them (University of Minnesota).

Chemical control

UW-Madison says control is rarely needed unless an area has a history of damage, and that several insecticides are labeled for grubs; follow labels that call for watering the product in. For adults on trees, it names carbaryl, cyfluthrin and lambda-cyhalothrin among contact products labeled for them, though adult leaf feeding is usually minor. Purdue's general grub timing applies: preventive products before egg hatch, curative products while grubs are small and feeding near the surface. Cornell sets a low threshold for these large grubs, about 3 to 4 per square foot, and UMass uses 2 to 4. Follow any bee-protection directions on the label. Use only products labeled for this use; the label is the law.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Expect waves: after a big beetle flight, watch lawns closely the following spring and summer.
• Keep turf vigorous with sensible watering and feeding so it can outgrow light damage.

When to call a pro

Call a licensed pesticide applicator (see our pesticide applicator license guide) if large grubs are killing turf in an area with a history of damage. For heavy leaf loss on oaks or other large trees, call an ISA Certified Arborist.

Related guides: Weed identification guide · All pests and diseases

Questions about may/june beetles

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