Cluster flies are an annoying group of flies. Their larvae feed on earthworms in grass in pasture and lawns. Find out how to stop them invading your home this season.

What Are Cluster Flies?

Cluster flies are large, slow moving, hairy, flies around 10-15mm with a dark gray to black non-metallic abdomen. The larvae of the flies feed on earthworms in grass pasture or lawn areas. Then in autumn and early winter the adult flies will move into homes and other buildings to survive the winter.

They are named cluster flies because of their habit of congregating in large groups or swarms, often  in dark places such as attics, corners of dark rooms, ‘nooks and crannies’ and ‘cracks and crevices’. Each fly releases a pheromone (smell) that attracts others. This pheromone will linger on, even after all the flies have been destroyed and removed. Thus the pheromone will continue to attract cluster flies to that area and clusters will keep recurring. It is therefore important that treatments are continued even when there are no flies present.

Why Are They a Pest?

The flies congregate to survive through the winter and once warmer weather arrives in spring they emerge from their ‘hibernation’ to lay eggs on surrounding grassland, pasture and lawns. So there tend to be two times of the year that these flies bother us in homes and other buildings; autumn when they congregate and spring when they emerge from their hiding places.

How To Stop Clusters

Kill the adults to prevent them laying eggs in surrounding grass. Kill the larvae in the grass to prevent the adults clustering in your buildings.

If you, or a neighbour, have had the problem in the past treat the likely areas of clustering in early autumn to prevent clusters forming. Spray with residual surface spay as described.

If you have the adult flies swarming and clustering in the house or other building you need to carry out a full program of treatment.

  1. Check around your house/buildings for clusters of flies in warm, dark, dry corners specially your roof void and eaves.
  2. If these can be accessed, spray the clusters with a residual surface insecticide such as NO Bugs Super from Kiwicare. If the clusters cannot be found or accessed use a bug bomb such as NO Bugs in the voids.
  3. Once the flies in the cluster are dead, clear away as many bodies as can be reached. If you use a vacuum cleaner ensure the bag is disposed of immediately. Spray the surfaces they were clustering on with more NO Bugs Super to prevent new clusters forming where the pheromone lingers.
  4. Treat the surfaces around the home where flies have been seen and entry points to the roof void around the eaves etc. with NO Bugs Super.
  5. Treat again prior to the next season to prevent new clusters collecting. Given a chance they will use the same areas to form clusters.
  6. If possible it is best to prevent the problem of these flies moving into your home by treating the larvae in the soil before they become adult flies. Use soil insecticide such as NO Insects Lawngard Prills which is a slow release insecticide in the form of granules. This is an ideal product to protect you from Cluster flies and other soil pests such as grass grub and porina. Sprinkle the granules on grassy areas within 100-200m of your home and water in thoroughly. These flies rarely travel further than this to infest a home.

Stay Cluster Fly free this season.

Article Brought To You By Kiwicare     kiwicare-logo-50x50

Kiwicare is New Zealand’s own manufacturer and distributor of pest control, garden care and home maintenance products. The Kiwicare website contains advice on the eradication and prevention of all sorts of pests that bother us in New Zealand. Learn how to get rid of rats and mice, flies, spiders, ants, cockroaches, fleas, bed bugs and other creepy crawlies. Protect your plants from aphids, grass grub, caterpillars, weeds and more. Keep biting insects at bay with the Safari range of insect repellents. See the BioGro certified organic range of products to help you stay pest free without chemicals.

How To Stop Cluster Flies, 4.9 out of 5 based on 57 ratings



  1. The Kiwicare website has a great new look and many new features including interactive problem solvers for home pests and garden pests, diseases and health.
    You may find some of the links in this article try and take you to the page that no longer exists. The error page however will tell you go to the home page and you will easily find the new page on the subject you seek.

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    Rating: 4.3/5 (3 votes cast)
  2. Tony says:

    nobody seems to have suggested the obvious solution – flyscreens!

    I had a plague of flies for a couple of years and tried surface treatments and ordinary sprays, they still came back.

    In the end I went to Bunnings and bought some DIY flyscreen material and covered a window in each room. This fixed the problem and avoids the use of chemicals.

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    Rating: 2.0/5 (13 votes cast)
  3. Hi Tony,

    You are quite correct that fly screens are a great way to stop flies coming in open windows and I always recommend them as a first line of defense. However, cluster flies seach for and enter buildings via eaves and other such dark gaps. They are seeking places to hide and survive over winter. They tend only enter the living part of the home when the temperatures rise on a warm day or in spring.

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    Rating: 4.8/5 (6 votes cast)