The large, long-legged insect often called a “mosquito eater” is actually the crane fly. This common name is a biological misnomer, as the adult crane fly is completely harmless and does not prey on mosquitoes. While the adults pose no threat, their offspring are responsible for significant damage to turfgrass and lawns. Effective control requires understanding the true identity of the pest and focusing treatment on the specific larval life stage that causes destruction. This targeted approach ensures resources are used efficiently to protect turf.
Clarifying the Identity of Crane Flies
The massive, clumsy fliers resembling oversized mosquitoes are crane flies, members of the Tipulidae family. Despite the widespread belief that these insects consume mosquitoes, the adults are anatomically incapable of killing or eating other insects. The adult stage is short, focusing primarily on reproduction, and many species do not feed at all. If they do feed, they typically consume only flower nectar.
Crane flies are characterized by their slender bodies and extremely long, fragile legs that easily detach. The adult poses no threat to humans, as it does not bite, sting, or transmit disease. Identification is confirmed by a distinct V-shaped groove on the thorax. The adults are not the target of pest management, but their presence signals the start of the next generation.
Targeting the Destructive Larval Stage
The actual damage to turf is caused by the crane fly larvae, known as leatherjackets due to their tough, grayish-brown skin. These larvae feed aggressively on the roots, crowns, and shoots of turfgrass, causing the grass to weaken and die. This feeding typically results in irregular brown or yellow patches in the lawn, with damage most noticeable in the late winter and early spring.
Adult females deposit eggs directly into moist soil, usually in late summer or early fall. Newly hatched larvae begin feeding immediately and continue throughout the fall, overwintering in the soil. Feeding resumes vigorously in the spring as temperatures rise, before the larvae pupate in late spring or early summer. The destructive stage is most susceptible to control during these active feeding periods in late fall and early spring, when the larvae are relatively small and close to the soil surface.
Biological and Cultural Control Strategies
Effective management of leatherjackets often begins with non-chemical methods, which are both safe and sustainable for the long term. One effective biological treatment involves entomopathogenic nematodes, specifically species like Steinernema feltiae. These microscopic, naturally occurring roundworms actively seek out and penetrate the leatherjacket larvae in the soil. Once inside, the nematodes release a symbiotic bacteria that kills the host within 48 hours.
Successful application of beneficial nematodes requires specific environmental conditions for survival and movement through the soil profile. The soil must be moist before and after application, and treatment is best applied when soil temperatures are between 50°F and 86°F. Because ultraviolet light is lethal to the nematodes, they must be applied during the evening or on a heavily overcast day. Application should be timed for late summer or early fall when the new generation of leatherjackets is small and most vulnerable.
Cultural practices also play a significant role in reducing the severity of crane fly infestations. Since adults prefer saturated soil for egg-laying, reducing irrigation in late summer and early fall makes the lawn less attractive. Improving soil drainage through aeration and reducing excessive thatch buildup helps to create a less hospitable environment for the moisture-loving larvae. Another technique involves soaking an affected area and covering it with plastic sheeting overnight, which forces the larvae to the surface for collection and removal.
When and How to Use Insecticides
For severe infestations where the larval count exceeds an acceptable threshold, chemical control may be necessary to protect the lawn. Successful treatment relies on timing the insecticide application to correspond with the larvae’s active feeding periods. Systemic insecticides, such as those containing imidacloprid, or certain pyrethroids are effective when applied in the late fall or early spring. These chemicals must be watered into the soil immediately after application to reach the feeding zone.
It is absolutely necessary to read and strictly follow all instructions on the product label before application. The label specifies the correct application rate, required protective equipment, and safety precautions regarding pets and children. Treating at the wrong time, such as during summer pupation or after extensive spring damage, yields poor results. Homeowners should note that broad-spectrum insecticides can negatively impact beneficial insects, emphasizing the importance of targeted timing.