European crane fly
Tipula paludosa
6 host plants
Last updated
European crane fly larvae are large, wrinkled, grayish-brown maggots that feed on grass roots and organic matter in moist soils. You will see adult flies, which resemble giant mosquitoes but do not bite, emerging in fall and winter. Larvae damage turf and young plant roots, creating bare patches and wilting. Damage is most severe in wet years and poorly drained sites.
Improve soil drainage through aeration and amendment to reduce pest habitat; crane fly larvae require very wet conditions. Allow beneficial parasitoid wasps to establish in turf; they parasitize larvae effectively. No broad-spectrum insecticides are recommended; the pest pressure in home settings is usually tolerable. Accept some turf damage as a cost of growing grass in wet climates. Overseed damaged areas in spring after soil dries.
Quick Reference
Monitoring & Action
Pull back brown turf in February-March and count larvae per square foot. Threshold: 25+ larvae per sq ft warrants treatment; below that, turf can outgrow damage. Soap flush (flush method) forces larvae to surface for counting. Distinguish crane fly damage from compaction, drainage, or shade stress - these are more common causes of winter/spring lawn decline in maritime PNW conditions.
25+ larvae per square foot in maintained lawns; 15+ in high-value turf. Below this threshold, healthy turf can outgrow damage without intervention. Most lawns showing brown patches in February-March are below threshold. Confirm presence and count before treating.
Larval feeding on grass roots and crowns creates irregular brown patches in lawns, typically visible February through April when larvae are largest and soil warms enough to stimulate feeding. Damage intensifies through spring as third and fourth instar larvae consume increasing amounts of root tissue. Feeding severs roots and crowns, causing grass to pull up easily. Secondary damage from birds (crows, starlings, robins) excavating turf to reach larvae compounds the visual impact. In severe infestations (25+ larvae per sq ft), entire lawn sections may die. Damage is often misattributed to winter dormancy, compaction, drainage problems, or shade stress.
Cultural Controls
- Maintain dense, healthy turf through proper mowing height (3 inches), overseeding bare spots, and improving drainage. A thick stand of grass outcompetes whatever feeding pressure larvae create. This is prevention, not treatment.
- Reduce irrigation in September during egg-laying period. Eggs require moist soil surface for survival; dry conditions during the 2-week egg-laying window significantly reduce next year's population. Resume watering once egg-laying period ends (mid-October).
- Overseed damaged areas in early fall or spring. Fast-establishing perennial ryegrass fills in quickly and competes with larvae.
Host Plants (6)
European crane fly is one of the most common lawn pests in the Puget Sound lowlands. The maritime climate with wet falls, mild winters, and moist springs is ideal for this pest. Introduced to British Columbia in the 1960s, it reached Washington state by the early 1980s. The wet September conditions typical of this region favor egg survival. Most homeowner complaints arise in February-April when brown patches appear. Damage is frequently overdiagnosed; many brown patches blamed on crane fly larvae are actually caused by poor drainage, compaction, or shade. Always confirm with a larval count (25+ per sq ft threshold) before treating.
— Chris Welch, ISA Certified Arborist
Sources & References
Primary: PNW Insect Management Handbook
- WSU HortSense European Crane Fly
- OSU Extension EM-9296: European Crane Fly — A Lawn and Pasture Pest
- WSU Turfgrass (Puyallup) European Crane Fly management
- UC Davis IPM European Crane Fly