Adult scarab beetles lay their eggs in lawns. The larval stages of the beetle pose a danger to turf grass due to their voracious feeding habits. Approximately nine species of dark scarab beetles occur on home lawns; May/June beetles (Phyllophaga species), black turfgrass Ataenius (Ataenius spretulus), green June beetle (Cotinis nitida), Japanese beetle (Popillia japonica), Oriental beetle (Exomala orientalis), Aphodius beetles (Aphodius granarius), bluegrass billbug (Sphenophorous parvulus), northern masked chafers (Cyclocephala borealis) and false Japanese beetle (Strigoderma arbicola).
The scarab beetles all sport hard bodies but vary in colouration, size and shape. May/June beetles have chestnut brown body. The Ataenius and the Aphodius beetles have black bodies. The northern masked chafers have shiny brown bodies withdark brown facial masks. Metallic green in colour, the green June beetle has a brown stripe on the sides of its body and brown legs. The Japanese beetle has a greenish metallic body with tan colouration and the false Japanese beetle looks similar but without the metallic sheen. The Oriental beetle is often light brown to black. The bluegrass billbug is a bluish-grey with a long facial snout.
The grubs of scarab beetles all share a similar appearance. The insects appear white, c-shaped and have six legs. Depending on the species, the grubs vary in size and thickness. The head of the grub is usually dark brown or orange coloured and the abdomen sometimes appears tan to brown in colour. Grub identification usually requires an expert who will be able to observe the hairs and sutures on the abdomen of the grub's body.
Adult scarab beetles do not feed on the lawn but they often feed on trees, shrubs and ornamentals. The grubs of the beetle feed heavily on the roots of the grass. Their feeding causes the lawn to turn yellow and brown. Large dead areas often appear with a severe infestation. The life cycle of each beetle is unique but some grub species, such as the May/June beetle, persist in the lawn until the grubs are three years old before they emerge from the turf as adult beetles.
Scarab beetles enjoy laying their eggs in moist, open lawn areas. Egg laying usually occurs during the night. Avoid extensive watering during June and July when the beetles are the most active and lay their eggs. If moderate lawn damage does occur from beetle grubs, fertilise and maintain the lawn so it can overcome the damage. The best control is gained when pesticides such as imidacloprid and thiomethoxam are applied when you first observe the adult beetles on the lawn and the beetles are laying eggs.