Issue 8, June 11, 2012
Anthills are commonly a problem in golf courses, lawns, and flower beds. They are primarily an aesthetic problem due to their unsightliness. Control of ants is commonly requested by homeowners but rarely warranted. On golf greens, they can hinder play. Some ants build large nests that stick up high enough to impede mowing.
Attempts at general control of ants in turf are rarely successful due to their high numbers in urban environments and their ability to colonize new areas. An understanding of their habits makes it easier to cope with these very common insects. There are about 90 species of ants in Illinois. Different species vary from each other in size, color, and other characteristics, including where and how they live. What follows is a generalized coverage of ants that typically live in turf areas.
Although ants are familiar to everyone, they can be identified by their very obvious 3-body regions of head, thorax, and abdomen. Ant antennae are elbowed, having a sharp bend about a third of the way out from the head. There is a very obvious constriction between the leg-bearing thorax and the abdomen that is the hindmost large body area. This constriction produces an hourglass-shaped waist that will have a bump, node, or sharp-angled structure on it. The combination of these characteristics separates ants from other insects.
Ants live in colonies which are most often seen in turf as anthills, each being a hole in the ground that is about 1/4 inch in diameter with a mound of fine soil around it that is usually 2 to 3 inches in diameter. Each colony has several classes or castes of individuals. There will be 1 or more wingless queens that are usually the largest ants in the colony. Queens lay the eggs that keep the colony going.
These eggs hatch into legless, white larvae, which are kept underground in the anthill's tunnels and fed by the workers. Mature larvae pupate and emerge several days later as adult ants. Most mature larvae and pupae are about as large as the workers. When an anthill is disturbed, the mature larvae and pupae are carried to safety by the workers and are commonly called eggs by most people. Ant eggs are also white but are much smaller.
Most of the individuals in a colony are wingless workers. These are non-reproductive females that do everything but the egg-laying for the colony, including cleaning the tunnels, feeding the larvae, expanding the tunnels, feeding the queen, gathering food, and defending the colony. In some species of ants, those workers that defend the colony are larger than the other workers.
Usually two or three times a year, winged males and females called reproductives emerge from the colony. This will occur in all of the colonies of the same species on the same few consecutive nights. These winged ants look like the worker ants except that they are larger and have 2 pairs of wings; the first pair is much larger than the second. These winged reproductives mate and then select a site to start a new colony. They shed their wings and tunnel into the soil to construct a new anthill.
Ants are quite variable in their feeding habits, but most of them are scavengers and predators that take advantage of situations as they occur. Soft-bodied, slow-moving insects and other small animals that are poor at defending themselves--such as sod webworm larvae, small cutworms, and small grubs--will be killed and taken back to the colony for food if they are found by foraging ants. Ants more commonly scavenge dead insects, decaying plant parts, and other debris for food and take it back to the colony.
The tunnels of their anthills serve to loosen the soil, allowing air and water to more easily enter. Recent research has determined that the ants in a typical lawn are more effective in aerating the soil than earthworms. Small numbers of turfgrass plants may die as a result of the removal of soil near the roots and the drying out of roots where an anthill is constructed. Some species of ants will construct large anthills that may kill the turf in a 1- to 2-foot diameter and stick up into the air high enough to be hit by mowers. Ants' scavenging activities help to recycle nutrients back to the turf.
Large ant hill.
Large anthills can be killed by opening up the top of the anthill to expose the tunnels and then applying Bifenthrin (Onyx), deltamethrin (Deltagard), permethrin (Astro) or other labeled pyrethroid insecticide into the colony. Within a few weeks a new anthill will likely appear in the area, but it will probably be an ant species that will not build such a large anthill. Even small anthills may warrant control on golf-course greens. Ants and their anthills may need to be controlled with an insecticide application where new sod is being laid because their tunneling activities under the loose sod will allow the roots to dry out and reduce the likelihood of the sod's surviving.
Ant hills on a golf course.
Attempting to control small anthills over an extended time in turf is not recommended. The various reasons that are given for desiring control include their causing bumps as the mower runs across them; their being a source of ant infestation indoors; their sheer numbers, often considered harmful; and their very existence. None of these are valid reasons for control. Ants are so numerous that areas where the anthills have been killed with an insecticide will be colonized by new ones as soon as the insecticide residue degrades, usually in about a month. Repeated control efforts will result in recolonization of the areas with ants. If there is no other reason for avoiding general ant control in turf, the fact that control is so short-lived against an insect that causes no apparent harm should be reason enough. (Phil Nixon)