Lawn Pests in North Dakota (continued)
E-904 (Revised), April 1997
Sod Webworms
White Grubs
Ants
Earthworm
Other Pests Associated With Lawns
Additional Readings
Ants
Ant species discussed in this report are
attracted to lawns because this habitat provides sites for their
nesting activities. There are about 10 species of ants that can
establish nests in or around lawns and houses. None feed directly
on grasses but can utilize seeds, secretions and other insects
that are attracted to the lawn habitat. Most ant activity is
beneficial, but nesting activity at times becomes unsightly and
may annoy homeowners.
Damage symptoms: Any damage associated with ants is due to the activities of the worker or foraging caste of ants. Harvester ants may remove the grass from around their nests. This produces large bare patches. Ants which culture aphids on grass roots can cause indirect damage due to aphids feeding on the grass. In addition, ants may damage the grass roots around the colony while excavating galleries. Large mounds produced by certain species may detract from the appearance of the lawn as well as make mowing difficult. Some common lawn inhabiting ants are very aggressive and can attack when their colonies are disturbed, inflicting a painful sting. Ants may invade homes during foraging activities causing distress to homeowners.
Biology and life cycle: Ants can sometimes be identified by their nest building habits or food preferences. The western harvester ant is a seed gatherer. It produces large pebble-covered mounds and frequently clears the vegetation from large patches of lawn. The silky ant produces low, medium sized earthen mounds, tends aphids on plants and scavenges dead insects for food. The other species found in lawns produce small inconspicuous mounds or no mounds at all. The activities of ants are most obvious following rains when they reexcavate their collapsed galleries and deposit soil particles on the surface. Most lawn ants collect honeydew and scavenge for dead insects and seeds as food.
Figure 8
Adult ants in a colony include a fertile female queen (Figure 8c), sterile female, workers (Figure 8e), winged males (Figure 8a) and virgin queens (Figure 8d). Virgin queens and males have two pairs of wings. The queen is the largest ant in the nest, often being twice the size of the workers. Males may be almost as large as the queen and the workers are the smallest individuals in the colony.
When temperatures drop in the fall, ants become less active and congregate in the deeper chambers of the nest where they pass the winter. In the spring, ant activity resumes and they move to the upper chambers of the nest to reproduce and collect food. Within the colony, the queen lays eggs (Figure 8g) and workers tend to the queen. Worker ants maintain the colony by foraging for food and tending the young (Figures 8b and f). Several generations of young are reared each summer.
Queens and males are produced once during the season by each colony. Winged males and winged virgin females leave the colony to mate and form a new colony. Timing of the emergence of reproductives varies from species to species. After mating, the males die. Fertilized queens search for a nest site, strip their wings and excavate a brood chamber. Within this brood chamber, the queen lays and rears the first brood of workers. As the first brood of workers become adults, they take over the colony maintenance, foraging and brood care. The queen's role in the colony is solely egg laying once the nest is established. A queen may live for many years. The actual life span of a queen is species dependent and in some colonies she may be replaced several times during the life of a colony.
Natural enemies: Ants are parasitized by a number of species of parasitic wasps and are preyed upon by birds, reptiles, amphibians and predaceous insects. Most parasitism and predation is directed at the worker caste and has little impact on a healthy colony.
Sampling methods: There are no established methods to sample quantitatively for ants in lawns. Treatment is only warranted if ant activity in the lawn produces unsightly mounds or bare patches.
Cultural practices: Cultural practices have little impact on ant activity, but proper lawn maintenance will enhance a lawn's ability to withstand and recover. The activity of most ant species are beneficial to lawns since they aid in soil aeration and feed on harmful insects.
Earthworm
This category is a complex of species
that includes night crawlers, garden earthworms and red worms
(Anellida: Lumbricus spp.). These animals are segmented
terrestrial worms that normally inhabit healthy lawns with their
presence seldom causing alarm. Earthworms are found in almost any
soil which has adequate moisture and nutrients.
Damage symptoms: Very high earthworm populations may disrupt the roots of grass and plants in the lawn. The main concern to homeowners is the castings left on the soil surface that make the ground uneven and the lawn unsightly. The castings are evidence of worm digging activity because worms must eat their way through the soil and excrete the ingested soil on the surface. As these castings dry, they become hard and unpleasant to walk over.
Biology and life cycle: Earthworms are most abundant in moist heavy soil situations. Earthworms will migrate deep in the soil during the fall and return toward the soil surface in the spring. During the summer months, the proximity of earthworms to the surface depends upon the availability of soil moisture. Earthworms (Figure 9) are long and tubular. They have approximately 150 segments with the skin being covered with a secreted lubricating mucus. Each body segment possesses bristles that can be felt if the finger is rubbed against the underside of the worm. The worms also possess a distinctive raised smooth structure, the clitellum, about a third of the distance from the anterior end.
Figure 9
At night during spring and early summer, earthworms will mate and deposit fertilized eggs within a cocoon on or near the soil surface. Each cocoon will contain from two to 20 eggs with an average of four. The cocoons are oval and approximately 1/8 inch long, with the eggs hatching in two to three weeks. Once hatched, the young worms begin tunneling and feeding in the soil.
Natural enemies: Earthworms are preyed upon by ants, centipedes, birds, snakes, beetle larvae and toads. They are also parasitized by species of protozoa, nematodes, fly larvae and mites.
Sampling methods: There are no established methods of sampling for earthworms in lawns. The presence of earthworms can be determined by finding castings in the lawn or earthworms on the surface of the soil or sidewalk following a rain. Control is necessary only when the earthworm population develops to levels that damage the lawn or when castings severely roughen the surface of the lawn.
Cultural practices: Routine lawn maintenance schedules indirectly benefit worms. The healthier the lawn, the more attractive it is to earthworms. Worms, for the most part, benefit the lawn by recycling nutrients and aerating the soil. Excessive castings left by worms may be flattened with either a power rake or a weighted lawn roller when the surface of the soil is damp. Annual power raking each spring is often sufficient to destroy castings from season to season.
E-904 (Revised), April 1997
