The crane fly is a common insect belonging to the extensive family Tipulidae (Order Diptera), which contains over 15,500 described species globally. Often mistaken for a giant mosquito, crane flies are one of the most diverse groups within the true flies. They are found across the world, thriving in temperate and tropical regions where moisture is readily available, and are a familiar sight in gardens and homes.
Physical Characteristics and Common Misconceptions
Adult crane flies are easily recognized by their long, slender bodies and extremely delicate, disproportionately long legs, which often break off easily when handled. The body of the larger species can measure up to 1.5 inches in length, with a wingspan that can reach up to 2.5 inches. They possess a prominent V-shaped suture on the top of their thorax, a distinct feature of the Tipulidae family.
The most persistent misconception is that these insects are “giant mosquitoes” or “mosquito eaters” that bite humans or animals. Adult crane flies are entirely harmless, as they do not possess the mouthparts necessary for biting, stinging, or feeding on blood. Many adults do not feed at all, relying on energy reserves from their larval stage, or they may only consume nectar or water.
The Complete Life Cycle
The crane fly undergoes a complete metamorphosis, progressing through four distinct stages: egg, larva, pupa, and adult. The adult female typically lays her small, dark, oval-shaped eggs directly into moist soil or turfgrass shortly after emerging, sometimes depositing up to 300 eggs. The eggs hatch quickly, usually within one to two weeks, and the newly emerged larvae begin their lengthy developmental stage.
This larval stage, commonly known as “leatherjackets” due to their tough, leathery skin, is the longest phase of the life cycle, often lasting for months and sometimes overwintering in the soil. These cylindrical, worm-like grubs can reach 1.5 inches when fully grown. After months of feeding, the larva transitions into a pupa just beneath the soil surface for approximately two weeks before the adult fly emerges in late summer or early autumn.
Impact on Lawns and Gardens
While the adult crane fly is benign, the subterranean leatherjacket stage is responsible for damage to lawns and gardens. The larvae feed voraciously on the roots, crowns, and occasionally the shoots of turfgrass, especially during the cooler, moist seasons of fall and spring. This root-feeding weakens the grass, leading to visible damage that appears as irregular, yellowed, or brown patches.
A severe infestation is often indicated when the affected turf pulls up easily, as the root system has been significantly damaged. Furthermore, the presence of large numbers of leatherjackets attracts secondary damage from predators like birds, skunks, and raccoons, which dig up the turf in search of the larvae. The extent of the damage is often greater in heavily irrigated lawns or areas with poor drainage, as the larvae thrive in saturated soil conditions.
Management and Non-Chemical Control Methods
Controlling crane fly populations is most effective when focused on the vulnerable larval stage, which is active in the soil. A proactive approach involves cultural controls that make the environment less hospitable to the egg-laying adult females. Reducing excessive irrigation and improving soil drainage are highly effective, as the insects prefer to lay eggs in consistently wet areas.
Practices such as lawn aeration and dethatching help to reduce the thatch layer and improve soil health, making the turf more resilient to minor pest pressure. Maintaining a healthy, well-fertilized lawn helps the grass tolerate higher populations of leatherjackets without showing significant visible damage. For a direct, non-chemical intervention, the application of beneficial nematodes, specifically Steinernema feltiae, can be highly effective.
These microscopic roundworms (Steinernema feltiae) are applied to moist soil in late summer or early autumn, where they actively seek out and infect the young larvae, providing a biological control measure. Lightly rolling the lawn can also physically crush larvae near the surface, especially when done in the early morning. If an infestation is localized, reducing moisture and encouraging natural predators like starlings and robins will help keep the population in check.