Crane flies are large, gangly insects often mistaken for giant mosquitoes due to their long legs and slender bodies. These insects are harmless and do not bite or sting, but they can become a nuisance when they swarm around your home. Adult flies are attracted to light sources and structural gaps, seeking warmth and shelter after emerging from the soil. Implementing exclusion and population control strategies can effectively prevent these visitors from clustering near and entering your living spaces.
Eliminating Exterior Light Attraction
Crane flies, like many nocturnal insects, are strongly drawn to artificial lights. This attraction is rooted in their natural navigation system based on the moon. The bright, concentrated light from porch or security fixtures confuses this system, causing the flies to cluster around the source. To minimize this, homeowners should replace traditional bulbs that emit light across the full spectrum.
A switch to warmer-colored light sources is an effective deterrent. Insects are less attracted to light with longer wavelengths, such as yellow or amber. Consider replacing standard incandescent or cool-white LED bulbs with specialized yellow incandescent “bug lights” or warm-white LED bulbs with a correlated color temperature (CCT) below 3000 Kelvin.
The strategic timing of exterior lighting can also reduce the congregation of flies near your home. Using motion sensors on security lights ensures illumination only when necessary, limiting the time flies have to become attracted to the area. For decorative or porch lighting, utilizing a timer to turn lights off earlier in the evening will lower the draw. It is also helpful to draw interior window blinds or curtains at night to prevent light from spilling outside and attracting flies closer to the structure.
Sealing Access Points
Once adult crane flies are drawn near the house, they will exploit any gap to gain entry. A thorough inspection of the home’s perimeter is necessary to identify and seal these access points. Damaged window and door screening is a common entry point and should be inspected for tears or holes. Small punctures can be repaired with adhesive screen patches, but severely damaged screens should be replaced.
The integrity of seals around doors and windows also requires attention, as worn materials compromise the barrier. Replacing old or flattened weather stripping around door frames and windows helps to eliminate the thin gaps that allow insects to crawl inside. Additionally, installing a tight-fitting door sweep on all exterior doors closes the space between the door bottom and the threshold.
Gaps around utility entry points, such as where pipes, cables, or vents penetrate the exterior walls, are frequently overlooked. These openings should be sealed using appropriate materials. Small cracks can be filled with a high-quality, exterior-grade silicone caulk, while larger voids around conduits can be blocked with expanding foam sealant or copper mesh.
Reducing Lawn Populations
The most effective long-term strategy involves addressing the source of the problem: the larval stage, commonly known as leatherjackets, in the lawn. Adult crane flies emerge from the soil in late summer and early fall to lay their eggs. The resulting larvae feed on turf roots throughout the fall and spring, thriving in moist, damp soil conditions.
Improving lawn drainage and managing irrigation is a foundational practice to deter egg-laying. Adult female crane flies actively seek saturated soil for oviposition. Reducing or pausing irrigation in the late summer, particularly in September, can reduce the survivability of eggs and young larvae. Aerating compacted soil and dethatching the lawn creates a less hospitable environment for the larvae.
When populations are high, a biological control method is a safe and environmentally friendly option. Specific entomopathogenic nematodes, such as Steinernema feltiae or Steinernema carpocapsae, are microscopic worms that parasitize leatherjackets in the soil. These nematodes should be applied in the fall, typically two weeks after the adult flies are observed laying eggs. Application should occur when the larvae are small and feeding near the surface, and the soil temperature is above 50°F. This treatment reduces the number of larvae that survive to become nuisance adults the following year.