Heterorhabditis bacteriophora
Grub nematode (Hb)- Rate
- 250k–500k /m²
- Temp
- 12–35 °C soil (sources vary)
- Best for
- Drench on moist turf while grubs are feeding near the surface
Pest
June bugs
Phyllophaga spp. (May/June beetles)
The short answer
June bugs, also called May beetles or May/June beetles, are the many species of Phyllophaga: stout, solid brown to black beetles 1/2 to 1 inch long that fly at night in May and June and crowd round porch lights. The adults feed on the leaves of trees and shrubs, especially oaks and maples, but the holes they leave rarely matter and extension services say control is seldom warranted. The grubs are the real pest. They live in the soil for two to three years and chew grass roots, doing most damage in their second year. For lawn damage, treat them as white grubs: count first, then act.
hero macro · brown May/June beetle on a screen at night
An adult Phyllophaga beetle drawn to a porch light. Photo: pending.
Identification
Adults are oval, stout and heavy-bodied, 1/2 to 1 inch (about 13–25 mm) long, light tan to reddish-brown or black, and without patterns. Kentucky Extension describes the common May beetle as solid brown and 3/4 to 1 inch long. They fly clumsily at night, buzz round lights and thump into window screens. Sources give anything from about 100 to more than 400 North American species; they are hard to tell apart and the differences rarely matter to a gardener.
The grubs are C-shaped, cream-white with a yellow-brown head and three pairs of legs, and big when full-grown: sources give from about 1 inch (Utah State) up to 2 inches (5 cm, Missouri Conservation). The raster, the pattern of spines on the underside of the tip of the abdomen, is the reliable way to separate them from Japanese beetle and chafer grubs, and a 10× hand lens is enough to see it. Two other beetles are also called June bugs. The green June beetle (Cotinis nitida) is 3/4 to 1 inch long, metallic green with tan or bronze margins, and flies by day. The ten-lined June beetle (Polyphylla decemlineata), common in the Pacific Northwest, is 22–28 mm long, and hisses and squeals when handled.
Easily confused with
- Green June beetleAlso a pestAlso called a June bug, but metallic green with bronze to yellow edges, nearly 1 inch long, and it flies low over lawns by day in mid to late summer. May/June beetles are plain brown and fly at night.
- Ten-lined June beetleAlso a pestThe Pacific Northwest "June bug": a large beetle, 22–28 mm (about 1 inch), that also comes to lights at night but hisses and squeals when handled. May/June beetles are plain brown and silent.
- Masked chafersAlso a pestAlso brown and also drawn to porch lights, but only about 1/2 inch long and flying over the turf at dusk. The common May beetle is 3/4 to 1 inch.
Damage symptoms
What you see first is usually the adults, which are harmless to people and do little lasting harm to trees. Adults feed at night on the leaves of trees and shrubs, and in occasional outbreak years have noticeably stripped oaks and maples. Ohio State notes that the trees recover because the beetles fly for only a few weeks. The lawn damage comes from the grubs, and it looks like any other grub damage.
- Brown beetles buzzing round porch lights and thumping into window screens on warm nights in May and June
- Small, irregular holes in oak and maple leaves, or leaves eaten back to the main veins in outbreak years
- Yellowing, then brown patches of turf that pull up easily, with few roots left
- Skunks, moles, crows and grackles digging in the lawn for grubs
- Green June beetle only: small mounds of loose soil in the turf, like worm casts, and grubs crawling on their backs
Lifecycle & degree days
Most Phyllophaga take two to three years to go from egg to adult, depending on species and latitude. Adults emerge in May and June, feed and mate at night, and lay eggs in the soil. The grubs feed through the first summer and autumn, go deeper for winter, and come back up to feed through a full second season, when they are largest and do the most harm. They pupate in the soil; adults formed in autumn stay underground until the next May or June.
- Generations
- One every 2–3 years for most species; sources give 1–5 years across the genus
- Adults fly
- May and June, at night
- Eggs
- Spherical, white, laid in the soil
- Worst grub damage
- The grubs' second season in the soil
- Overwinters
- As grubs deep in the soil, or as unemerged adults
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Host crops
The grubs feed on grass roots in lawns and pastures. Kentucky Extension says they may be abundant in pastures but are not often a problem in managed turf, and Ohio State says the grubs prefer pasture grasses, so damage to trees is most often seen near pastures. Adults feed on the foliage of many trees and shrubs; oaks and maples are the ones most often reported.
Monitoring & action thresholds
Action threshold
2–5 May/June beetle grubs per ft²
About 20–55 per m². These are the lowest action levels for any lawn grub in both tables: UMass gives 2–4 per ft² and the Northeastern IPM Center 3–5 for unirrigated turf. There is no threshold for the adults. Maine and Ohio State say adult feeding on trees is usually insignificant and control is rarely warranted.
For grubs, sample the lawn as for white grubs: cut a square foot of turf on three sides in several spots, fold it back and count the grubs in the top 2 inches (5 cm) of soil. Check the raster to confirm the species, because thresholds and products differ. Adults at your lights are only a hint: May beetles fly to porch and street lights at night, so count grubs before deciding anything.
Beneficial
Biological control
Kentucky Extension says no biological product gives reliable control of white grubs, and nothing biological is sold for the adults. Grewal's turf review names the cruiser nematode Heterorhabditis bacteriophora as the best nematode for May/June beetle grubs, applied the same way as for other lawn grubs. Utah State lists nematodes and Beauveria products as biological options. Expect the same variable results as with other grubs. Milky spore does nothing to them: Kentucky Extension says May and June beetle grubs are unaffected by the strain sold. Skunks, moles and birds eat the grubs, and birds, bats and frogs eat the adults.
Cultural controls
The adults need no control, and turf that grows vigorously outgrows the root loss from a small grub count. Most of what works is the same as for other lawn grubs.
- Leave the adults alone — feeding on trees is short-lived and the trees recover
- Count grubs before treating; a few large grubs do not justify a treatment
- Keep turf healthy with sound mowing, feeding and watering, so it outgrows root loss
- Expect more beetle activity near pasture or rough grass, where the grubs are commoner than in managed turf
- Renovate badly damaged bluegrass or ryegrass with tall fescue, which tolerates grubs better
Chemical, last resort
Spraying adults at lights or on trees is not recommended: adult feeding is usually insignificant and control is rarely warranted. For grubs, Utah State advises a preventive soil insecticide in spring, and treatments work best on young grubs; Kentucky notes that overwintered grubs are large and hard to kill.Check any product before it goes on. Open the compatibility matrix →
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
Univ. of Maine Cooperative Extension, May/June Beetles (Home and Garden IPM fact sheet)
Ohio State BYGL, Night-Flying Buzz-Bumbling Beetles on the Wing (Boggs, 2016)
Univ. of Kentucky ENT-10, Controlling White Grubs in Turfgrass (M.F. & D.A. Potter, 1999)
Purdue Extension E-271, Managing White Grubs in Turfgrass (Richmond, 2023)
Ohio State Ohioline ENT-0107, White Grub Identification, Biology and Management (2026)
Utah State Univ. Extension, May/June Beetles (turf IPM pest note)
Univ. of Minnesota Extension, May/June beetles (garden insect diagnostic)
Missouri Dept. of Conservation, May Beetles (June Bugs) field guide
UMass Extension, Turf BMPs Section 11: Insect Management (threshold table)
Grewal, Using entomopathogenic nematodes for turfgrass pest management, Turfgrass Trends (2001)
NC State Extension, Green June Beetle in the Landscape (Baker, 2013, rev. 2023)
Washington State Univ. Entomology, Ten Lined June Beetle (bug info)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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