Cluster Flies life cycle and controlling methods

The insect kingdom comes with its own veil of surprises and you can find over 1 million varieties of insect’s right from the crawling ones to those with wings. One such insect species is the fly, which can be categorized under several sub-species including cluster flies. So what is a cluster fly and how is it different from other flies?

cluster flies

What is a cluster fly?

Native to Europe, cluster flies have over the years reached the shorelines of North America through their hosts – the earthworms. Ships sailing to North America containing earthworm ridden soil in their ballast were found to be the only mode of transport for these flies.

The cluster fly is known to belong to the genus Pollenia belonging to the blowfly family Calliphoridae. Although they share the same family, the cluster fly or Pollenia rudis is different from other blowflies like the bluebottle genus Phormia because this fly doesn't pose any health hazard.

They can be quite the nuisance from time to time and are known to lay eggs near earthworm burrows and not human food.

The cluster flies are considered to be parasitic in nature as their larvae feeds on earthworms. The adult flies emerge primarily in the autumn or even late summer. That is the time they can be quite a nuisance as they enter homes for purpose of hibernating. There is another reason why they are considered a nuisance - it is difficult to eradicate them as they hide in cavities and inaccessible spaces within a home.

Physical Appearance and Identification

Most often than not people can confuse the cluster fly to the common housefly and vice-versa. So, how do you really identify the species? The one big difference between the cluster fly and the common housefly is the hairs behind their head. The hairs of the cluster fly are golden in color.

The cluster fly can be distinguished from other flies of the same species through specific characteristics. The differences can be in basicosta coloring, thoracic coloring, and spiracle coloring. The size and shape of the cluster fly is also different and it is more oblong or egg shaped.

The adult cluster fly has a dark gray abdomen with black or silver-black checkers. The newly emerged cluster flies have several golden hairs

A newly emerged fly has many golden hairs on its thorax or the area between the neck and the abdomen. Over the period of time, the golden hairs are lost. One of the highly distinctive aspects of the cluster fly is the fact that it is slightly larger in size as compared to the house fly. The size is 9.525-12.7mm or 3/8-1/2 inch in length.

The coloring of basicosta or the basal part of the coxa (lateral side of the abdomen) of cluster flies can vary from yellow to almost light brown. The posterior spiracle (breathing tubes) is also different in color and range from mild yellows to light browns. The setae (bristles on the body) vary in number.

The cluster flies can have 6 to 8 hard frontal bristles and almost 2 to 3 rows of bristles situated along their thoracic section. These flies also have what is called aristate antennae, which looks like a pouch with lateral bristles.

Habitat and Behavior

Cluster flies are extremely different from the common housefly and hence their habitat and behaviors are also different.

These slow flying insects are a nuisance mostly during the warmer months. It is the winters when they will go into hibernation. So where do they hibernate? In your home!

Yes, it is true that cluster flies will begin to appear in your home or any building only during late summer and definitely around early autumn. When the days start becoming shorter and when the temperature starts to fall, these flies start their journey toward their overwintering sites, which could be your home!

It is not uncommon for the walls on the western and southern side of your home to become warmer and this is what plays a major role in attracting these flies.

Although, the cluster flies will enter through small openings like crevices and cracks in your wall and that will definitely become their most favourite place to dwell or hibernate.

You will find them mostly in the crevices close to your door frame, windows, and even attic.

Once these flies are inside your home, they will gather together to hibernate for the coming winter. There is also the possibility that too much of indoor warmth can interrupt their overwintering as their activity resumes at temperatures that are above 12 degrees Celsius.


One more thing, if your home has windows then you will find these flies heading towards the windows as well as any source of light during any warm days of the winter season.

If you have a home with open lawns that are spread large and wide with plenty of shade then it is the perfect place for cluster flies. This is how the flies tend to behave!

Feeding habits

The cluster flies are parasitic during the larvae stage and once they pupate, the adult flies become herbivorous. The major source of food for the larvae of cluster flies is earthworms and especially Aporrectoda chlorotica and Aporrectoda caliginosa species of earthworms. They also feed on other species including Lumbricus terrestris, Lumbricus rubellus, and Eisenia lucens genus of earthworms. Most of these species of earthworms exists in agricultural and garden soils and sub soils across the world.

The larvae feed on the earthworms till the time they reach the pupal stage. The adult cluster fly feeds on a variety of organic matter including flowers, plant sap, fruits, and even feces. They are also attracted to proteins, acetyl acetate and malt extract in animal meat.

Cluster flies life cycle

Even though, the cluster flies have arrived in North America from Europe, they have a different life cycle in Europe as compared to North America.

The female cluster fly prefers depositing eggs in humid areas especially in and around high soil moisture and dense surface vegetation. The flies can deposit a small cluster of 6-7 eggs or single eggs as well. The average number of eggs that a female cluster fly lays can vary from 100 to 130 eggs.

In North America, it takes between 27 and 39 days for the eggs to go from larvae to adult and in Europe, it can take anywhere from 10–12 months for the same process.

When the larvae hatch from eggs, they burrow into the garden soil using natural pore spaces. They keep moving through these pores to find host worms and then they penetrate the earthworm from the dorsal side. In order to survive they need to find an earthworm within three days of being born.

What causes cluster flies in my house all of a sudden?

Change in outside temperature and weather like seasonal changes can make cluster flies invade homes. If you suddenly notice hordes of cluster flies in your home then that is a sign that these flies are getting ready for their period of hibernation, which happens during the winter months.

Once they are inside your home, they will look for cracks and crevices behind doors, in door and window frames, and dark corners. It can at times become extremely difficult to find them once they go into hibernation. If you have an attic at home then you are surely to find them hibernating there.

Where do cluster flies come from?

Now that they are in your home, you are probably wondering where they came from. The answer is – right from your garden or any green area in or around your home. The green lawns right in front of your home is the breeding ground of the cluster fly. This is where the female fly lays eggs and they go from larvae to pupal to adult stage right there.

What do cluster flies eat?

What is the favorite food of cluster flies? The larvae loves to feed on earthworms but the adult fly feeds on anything from flower to plant saps and even fruits.

How long do Cluster flies live?

Cluster flies can live for 1-2 years and this is exactly the reason why they are considered as a home pest.

What attracts cluster flies?

Unlike the common housefly, the cluster flies are not attracted towards your garbage. The only thing that attracts them to homes is their need to hibernate during the winter months. Even during hibernation, they prefer to remain in clusters on the sunny side of your home or attic in the day time and go back into crevices during the night.

How do cluster flies get in the house?

Cluster flies can enter your home just the way any housefly would enter that is through doors and windows.

Damages caused by cluster fly

Cluster flies are considered a nuisance because they can invade your home in clusters during winter season but they don’t cause any damage as such. These flies don’t spread diseases but can leave a lot of fecal markings on the walls, doors, and windows. As a result, you will need to keep cleaning the walls and it can be a time consuming exercise.

If a cluster fly inhabiting within crevices in your home dies all of a sudden then they attract larder beetles, which can be quite the headache as you will have to put in place strategies to fight both cluster fly and larder beetle infestation.

How to prevent cluster flies

Prevention is always a better option when it comes to keeping cluster flies away from your home. The best solution is residual sprays or insecticides, which can be used before in homes and buildings before the start of winter season. The use of such sprays will repel these flies and hinder them from invading your home.

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