Beneficial Lawn Insects

Many insects that occur on lawns are beneficial. They provide a natural control of pest insects or assist in the breakdown of organic matter so nutrients can be returned to the soil. These insects are grouped into two classes: predators and parasites.

Predators

Predatory insects are relatively mobile insects that search out prey. Some predatory insects (like the assassin bug) have sucking mouthparts which penetrate the soft body of the victim and suck out the internal fluids, leaving only the outer shell behind. Other predatory insects (like ladybird beetles and ground beetles) have chewing mouthparts and feed on the entire body of the victim. Predators will feed on several victims during their lifetimes. Some of the more familiar predators that occur naturally in New England lawns include:

Ground beetles: These may be the most common predators on lawns in New England. The most common species are slightly smaller than Japanese beetles and are generally a shiny bronze or tan or green. Both adults and larvae feed on soft-bodied insects and various caterpillars. Ground beetles usually are very quick moving and can "seek and destroy" their prey.

Spiders: While they are not insects, spiders are surprisingly common and active in grass areas and are very efficient predators. Many species of spiders are beneficial in the garden or lawn, feeding on a wide range of immature insects and mites.

Ants: Some species of ants are carnivorous, seeking out insects and other soft bodied organisms with which to provision the nest. In addition, ant activity often can help in the general breakdown of organic matter and the formation of soil. However, if ant activity becomes excessive, the ants may become a nuisance or the soil may dry out and turf damage will result.

Parasites

Parasites are small insects (generally smaller than the host) that develop inside or on the body of a single individual. The adult female finds a suitable host and lays her eggs on the outside of the body or inserts the eggs through the skin into the internal tissue of the host. The immature parasites feed on the organs and fluids inside the victim which gradually weakens and kills the host. 

There are many parasitic wasps that occur naturally in New England and are active in lawn settings. Wasps such as scoliids and tiphiids are adapted to lay eggs in softbodied insects. Scoliid wasps are about 5/8 inch long and are blue-black, with blackish-purple wings and a yellow stripe on each side of the abdomen. Their bodies are fairly hairy and the back part of the abdomen is covered with reddish hairs. Tiphiid wasps are black and somewhat hairy with short, spiny legs. Both wasps are generally seen flying over the lawn during the day, leaving in early evening. These wasps are beneficial in that they parasitize grub populations. They are not aggressive and generally do not attack humans. Adults are often seen on golden rod flowers in the late summer.

Pest Management

Beneficial insects are very sensitive to insecticides, so whenever a general insecticide is applied to control a pest species the material will usually have a detrimental effect on the beneficial organisms, often for at least a few  weeks. Consider using alternate methods of pest management, biological control agents (if available and suitable),or providing optimum cultural conditions so that the lawn can tolerate higher levels of pest activity without visible loss of vigor. If an insecticide application is deemed necessary, make spot treatments rather than broad scale applications if at all possible.

Remember that the statement "The only good bug is a dead bug." could not be further from the truth. Be sure you have an accurate identification of the insects in question and only attempt to control those that really warrant attention. There are in fact many "good bugs" out there! Let them help!

Adapted from the University of Massachusetts Extension, 1999