If you’re like most people you’ve probably never heard of cluster flies. Chances are good, however, that you’ve seen some. They range widely across North America and look somewhat like large house flies. But there are significant differences.
First of all, cluster flies move more sluggishly and slowly than other species. Watching one you might think it’s lazy or ill, but that’s just its nature!
As their name implies, they live very close to one another and are prone to swarming when they detect light coming through windows or from lamps.
Cluster flies don’t hang out around trash cans or rotten stuff like their cousins. Instead, their larvae live inside earthworms in a parasitic relationship, feeding off their hosts. That’s why during summer months you’ll primarily find adults loitering around lawns and gardens where earthworms are abundant.
Migration
As fall sets in, adult cluster flies start looking for places to overwinter. They begin by migrating to the sunny sides of buildings (think south and west elevations). When truly cold temperatures arrive they move indoors through cracks and holes around windows, doors, plumbing, and electrical conduits. Even the smallest breach is enough for them to enter.
Once inside they gather tightly (or “cluster”) in wall voids, attics, and other out-of-sight locations. You may not even know they’ve moved in. I say “may”, because on warm winter days some may wake from hibernation and move toward windows or light fixtures.
Their annual cycle ends in spring as flies return outdoors to mate and lay eggs.
Lifespan at a Glance
We’ve seen that adult cluster flies don’t eat trash, so what do they eat? Like bees, they love flower nectar, plant sap, and juice from fruit. Since they don’t linger in germ-laden environments they’re less likely to transmit diseases, therefore don’t pose health problems like other species.
Females lay 100–130 eggs per season, depositing them in the dirt near earthworm burrows. They typically lay twice to four times a season, 20-40 eggs per cycle.
Eggs hatch in about 3 days, then larvae enter earthworms to feed for another 11–22 days. When developed, larvae exit their hosts and pupate in the soil for about two weeks. The length of development depends a lot on temperature, ranging from about 27–39 days in North America. Adults typically live two to three months, but those that overwinter in a warm, safe place can live over two years!
Prevention and Control
Pest control begins with prevention. Steps outlined below will prove effective against a wide range of unwanted rodents, spiders, and insects…cluster flies included!
- Seal Your Home: Before cool weather arrives, inspect your house and use caulk or weather-stripping to seal cracks around windows, doors, vents, eaves, and siding.
- Install or Repair Screens: Make sure the vent, window, and door screens are in good shape.
- Use Light Exclusion: When flies wake up on warm winter days their first reaction will be to move toward light. Block or dim bright interior lights to reduce attraction.
- Vacuum Often: If you see flies inside, suck them up rather than crush them. Dead flies can attract other pests. Dispose of residue in a covered outdoor garbage receptacle.
The Bottom Line
Cluster flies can be annoying, but they’re not particularly dangerous. They don’t bite, and they don’t spread disease like some flies do. The key is to block them from getting into your house in the first place — especially before fall — and then deal with any stragglers by vacuuming or applying an approved indoor pesticide designed for fly control.
What if despite your best efforts an infestation develops? Don’t panic! We are here to help! Contact KC Pest Control (405) 679-8729 at your earliest opportunity to arrange solutions for your pest problems! We have the skill, expertise, and materials to solve your pest problems…satisfaction guaranteed.
