**Crane Flies** (family Tipulidae) are large, slender insects often mistaken for giant mosquitoes due to their long legs and narrow bodies. They are generally harmless as adults, but the larvae, often called **leatherjackets**, can be serious pests of turfgrass, golf courses, and occasionally vegetable and forage crops, where they feed voraciously on the roots, crowns, and stems of plants near the soil surface. They are found globally, particularly in moist environments.
Taxonomy and Classification
Crane Flies belong to the family Tipulidae in the order Diptera (true flies). They undergo complete metamorphosis (egg, larva/leatherjacket, pupa, adult). The European Crane Fly (*Tipula paludosa*) and the Marsh Crane Fly (*Tipula oleracea*) are the two most common invasive species in North America that cause significant turf damage, especially in cool, moist coastal regions.
Physical Description
Adult Crane Flies are large, gray-brown, and slender, often measuring $1$ to $1\frac{1}{2}$ inches long, with an equally large wingspan. They are characterized by their extremely long, delicate legs, which are easily shed (autotomy). Their flight is often clumsy and weak. Despite their mosquito-like appearance, adults possess neither the mouthparts to bite nor any venom.
The **larva, or leatherjacket**, is the destructive stage. It is a tough-skinned, cylindrical, legless, grayish-brown grub, growing up to $1 \frac{1}{2}$ inches long. It lacks a distinct head capsule, and its tough, leathery exterior gives it its common name. Leatherjackets are found just below the soil surface, especially in the thatch layer of turf.
Distribution and Habitat
Crane Flies are globally distributed, often seen swarming near lights at night. The invasive pest species are concentrated in areas with mild, wet winters and cool summers, such as the Pacific Northwest and parts of the Northeast U.S. Their habitat is damp soil and saturated turf, where the larvae thrive. Adults are commonly found near water bodies or damp grassy areas.
Behavior and Life Cycle
The invasive species typically have one to two generations per year. Adults emerge in the spring and/or late summer/fall. Females lay small, black eggs directly into the soil or thatch of moist turf. The larvae hatch and begin feeding immediately.
The leatherjackets feed actively throughout the fall and resume aggressive feeding in the spring, especially when temperatures are mild. They cause the most damage just before pupation. They are primarily nocturnal, often crawling onto the surface of the grass to feed on stems and blades during the night or early morning hours.
Feeding and Damage
The damage is caused exclusively by the feeding of the leatherjacket larvae. They graze on the crowns and root tissues of the grass, severing the plants from the roots. Symptoms include:
- **Thinning, Brown Patches:** Irregular, yellowish-brown patches of dead or dying grass, especially in spring.
- **Root Severance:** In severe cases, the turf can be easily peeled back or rolled up like a carpet due to lack of roots.
- **Secondary Damage:** Birds (starlings, crows) and animals (skunks) actively dig into the turf to feed on the large, succulent larvae, causing extensive damage to the lawn surface.
Management and Prevention
Control focuses on the larval stage, often targeting the small, newly hatched larvae in the fall.
- **Cultural Control:** **Reducing irrigation** in the late summer/early fall can make the turf less attractive for egg-laying and larval survival. Aeration can also help.
- **Biological Control:** The use of **entomopathogenic nematodes** (*Steinernema feltiae* or *Heterorhabditis* species) is highly effective, especially when applied in the moist soil of the fall when larvae are small.
- **Chemical Control:** Insecticides are used, often applied in the early fall (to target small larvae) or in the spring (to prevent late-stage feeding damage), based on pest monitoring thresholds.
Conservation and Research
While the invasive species are pests, many native Crane Flies are harmless detritivores. Research focuses on distinguishing the invasive pest species from native, beneficial ones, and improving the timing and efficacy of biological control methods to reduce reliance on chemical treatments in turf management.