Crane flies are often described as oversized mosquitoes, appearing commonly in late summer and early fall. While the adult insects are harmless, their larvae, known as leatherjackets, feed aggressively on grass roots and shoots. This feeding creates patches of dead and thinning turf. Successfully eliminating these pests requires a targeted strategy that addresses both the immediate infestation and the long-term health of your lawn.
Identifying the Pest and Its Damage
The adult crane fly is a slender, long-legged insect that emerges from the soil in late August or September to mate and lay eggs in the turf. While adults live only a short time and cause no damage, their presence signals the start of the infestation cycle. The destructive phase is the larval stage, the leatherjacket, a grayish-brown, legless, and tubular grub with a tough, leathery skin. These larvae hatch in the fall and begin feeding on the grass.
Initial damage is often subtle, but leatherjackets resume aggressive feeding in the spring, which is when the most noticeable harm occurs. Look for irregular, brown, and sunken patches of dead grass that may be easily lifted due to the root severance. Another sign of a significant infestation is the increased activity of natural predators, such as robins, starlings, or skunks, which tear up the turf while foraging for the plump larvae. A population exceeding 15 to 25 leatherjackets per square foot often warrants treatment to prevent extensive turf loss.
Non-Pesticide Removal Strategies
Homeowners can use simple physical and cultural methods to reduce leatherjacket numbers before resorting to specialized products. One common technique is the “tarp trick,” which involves thoroughly soaking an infested area of the lawn in the late afternoon. Covering the area overnight with an opaque tarp forces the larvae to the surface due to saturated soil and lack of light. They can then be collected and disposed of the following morning.
Cultural controls focus on making the soil less hospitable, as larvae thrive in consistently moist conditions. Temporarily reducing irrigation where damage is suspected causes the surface soil to dry out, stressing young larvae or driving them deeper. Improving soil structure through aeration and dethatching also promotes drainage and increases the lawn’s vigor. A healthy, dense lawn is naturally more resilient to minor feeding damage.
Biological and Chemical Treatment Options
Effective control methods are divided into biological and chemical approaches, and timing is the primary factor for success in both. Biological control relies on applying beneficial nematodes, specifically insect-parasitic species like Steinernema feltiae. These microscopic roundworms actively seek out and infect the young larvae. They must be applied in late summer or early fall when the leatherjackets are newly hatched and most vulnerable.
For best results, nematodes require specific application conditions, including moist soil and protection from direct sunlight. They should be applied during cloudy weather or in the evening. The treated area must be kept consistently moist for up to two weeks afterward to allow the nematodes to travel through the soil and establish themselves. This biological approach is highly targeted and poses no risk to pets, wildlife, or non-target insects.
Chemical treatments involve the use of insecticides containing active ingredients such as imidacloprid, chlorantraniliprole, or carbaryl. Efficacy depends heavily on the larvae’s life stage. Like nematodes, these products are most effective when applied in the fall against the small, young leatherjackets shortly after the eggs have hatched.
Spring applications are generally less effective because the larvae are larger, tougher, and may be close to pupating, making them less susceptible to the chemicals. Homeowners should always check local regulations regarding pesticide use and follow the product label instructions precisely for proper application rates and safety protocols.
Long-Term Lawn Management for Prevention
The most sustainable strategy against crane flies is creating an environment that discourages adult females from laying eggs. Adult crane flies are strongly attracted to wet soil for egg deposition, making proper drainage a primary concern. Correcting underlying issues that lead to standing water or consistently soggy areas will significantly reduce the likelihood of a major infestation.
Adjusting your late-season watering routine is another simple, yet effective, preventative measure. Avoid excessive irrigation in late summer and early fall, which is the peak period for adult crane fly egg-laying activity. Maintaining a slightly higher mowing height, such as three inches, promotes deeper root growth and a more robust turf. A vigorous, deep-rooted lawn can often sustain a low population of larvae without showing significant visible damage.