The adult crane fly, often mistaken for a giant mosquito due to its long, spindly legs and slender body, is harmless. While the adults are a nuisance, the larval stage, commonly known as the leatherjacket, is the pest. These larvae feed on the roots and crowns of grasses just beneath the soil surface, leading to significant lawn damage. Removing these pests naturally requires a strategy that targets the destructive larvae by modifying their environment and introducing biological controls.
Identifying the Pest and Its Damage
The adult crane fly typically emerges in late summer or early fall, with the female quickly laying hundreds of eggs just below the soil surface. These eggs hatch into leatherjackets, which are grayish-brown, legless grubs that can grow up to two inches long and possess a distinct, tough, leathery skin. The larvae begin feeding in the fall, slow their activity during the cold winter months, and then resume feeding in the spring as they mature.
A crane fly infestation is often first noticed as irregular, yellowing, or dead patches of turf. If you can easily pull up sections of grass like a loose carpet, it is a strong indication that the roots have been severed by feeding leatherjackets. Another sign is a sudden increase in predatory activity, as birds, skunks, and raccoons tear up the lawn to feed on the protein-rich larvae. A healthy lawn can tolerate a small population, but counts exceeding 25 to 50 larvae per square foot warrant immediate control measures.
Cultural and Physical Control Strategies
Because crane flies prefer moist soil for laying eggs and larval survival, adjusting lawn watering practices is an effective preventative measure. Instead of frequent, light watering, switch to deep, infrequent irrigation to allow the top layer of soil to dry out between applications. In late summer, when adult flies are emerging and laying eggs, you can deliberately reduce irrigation to discourage egg survival.
Maintaining a slightly taller grass height helps to deter egg-laying and protects the lawn’s root system. Keeping your turf trimmed to a height of two to three inches exposes the soil surface to more sunlight, creating a less hospitable environment for the crane fly. Performing annual lawn maintenance, such as aeration and dethatching, further disrupts the leatherjackets’ habitat. Aeration reduces soil compaction and improves drainage, while dethatching removes the thick layer of organic matter where larvae often hide and feed.
Encouraging natural predators provides a continuous, passive form of pest management. Birds such as robins and starlings feed heavily on leatherjackets. For controlling adult crane flies near structures, simple physical barriers like sealing gaps around windows and doors can prevent them from entering homes. If an infestation is localized, covering the area with a dark, light-impervious material like black polythene overnight can draw the larvae to the surface for easy manual removal the next morning.
Biological and Targeted Natural Treatments
Eliminating an existing leatherjacket infestation involves applying beneficial nematodes. Specifically, the species Steinernema feltiae is a microscopic, insect-parasitic roundworm that infects the crane fly larvae in the soil. Once inside the pest, the nematodes release symbiotic bacteria that kill the leatherjacket within a few days.
Timing is crucial for the success of nematode application, as they must be applied when the larvae are small and feeding near the surface. The ideal time is in the late summer or early fall, typically August through October, about two weeks after the adult flies have been observed laying eggs. A secondary application can be made in the spring once the soil warms, as the larvae become active and move closer to the surface.
To apply the nematodes, the soil temperature must be between 59 and 79 degrees Fahrenheit, and the ground must be moist before and after application. Nematodes are sensitive to light and desiccation, so they should be applied in the early morning or late evening, followed by a light watering to wash them into the soil. Ensuring the ground remains evenly moist for several days after application allows the nematodes to move through the soil profile and locate their targets.
Another targeted natural option uses products containing azadirachtin, a compound derived from the seeds of the neem tree. Azadirachtin acts as a natural insect growth regulator, disrupting the leatherjacket’s development and feeding process. This product can be applied as a soil drench to target the larvae, providing a natural alternative to synthetic insecticides.