Appearance and Damage
The leatherjackets pupate in the early summer into adults. The adult European crane fly resembles an oversized mosquito. Harmless, the adults do not bite or sting. The adults emerge from the soil and begin breeding. During the late summer, the female crane fly lays her eggs. The larvae have a gray-brown leathery skin and measure up to 1 1/2 inches in length. They reside within the moist soil. The larvae damage the lawn by feeding on its root system, crown and shoots. A dense population of the larvae can cause the ground to develop brown spots.
The damage that the leatherjackets inflict on a lawn can resemble the damage other lawn pests cause. To determine if the leatherjacket larvae are the cause of the damage, consider digging up a 1-square-foot section of lawn to look for the pests. Dig the soil to a depth of 2 inches and peel the lawn back. A lawn in excellent health can often withstand up to 40 leatherjackets per square foot without sustaining damage.
Crane fly larvae rarely require insecticidal control unless a severe infestation exists. Apply insecticides from April 1 to April 15 to successfully manage the pests. Ensure that the pesticide will not harm birds, which aid in the control of the crane fly larvae. Spray the insecticide onto the lawn in the evening to help protect bees. Mow the lawn to remove any flowering clover or weeds that may attract bees who could suffer accidental poisoning from the insecticide.
Maintain the lawn's overall health to reduce the risk of damage from the leathernecks. Regularly fertilizing and watering the lawn will help build up its strength. Regular removal of thatch will help disrupt the crane fly's life cycle, which can lower the insect's population. Avoid scaring off starlings and robins from the landscape. Starlings and robins love to feast on the crane fly larvae. Ground beetles will also naturally hunt and kill leatherjackets in the garden.