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Do Flies Sleep?

Yes, flies require sleep just like humans. In reality, their sleep habits are surprisingly similar to ours. A fly’s daily routine is to actively carry out fly duties during the day, which mainly entails feeding, mating, and naps if necessary. They also need to rest and recharge at night, just as we do.

Most of us may never have seen a fly ‘sleeping,’ they are usually hidden away from sight. They will sleep anywhere they can to stay safe from predators. You may spot a fly sleeping on a wall, inside a cupboard, on a countertop, on leaves of plants, or anywhere around the home they have decided is safest.

Where Do Flies Go At Night?

Flies sleep just like we do, in several short naps throughout the night. They need to conserve energy and resources during the day and will therefore avoid unnecessary activity by sleeping at night. They will go anywhere at nighttime that has an ideal temperature and has a level of safety that they can sleep undisturbed.

Where Do Flies Sleep?

The location where a fly sleeps is typically fluid, it changes with each nap or rest period. Different locations provide different levels of protection from predators, so when in doubt a fly will choose its sleeping place based on the existing level of safety. For example, a fly will find a leaf or an open cupboard and sleep there.

Flies also like to keep themselves hidden from view when sleeping, so if they can’t find an ideal hiding spot, places such as the ceiling and behind blinds are ideal. They can also have daytime naps for short periods of time (around 10 minutes) before waking up, so it is common for them to just rest on the side of a window or wall if there are no hiding spots available.

The ideal temperature for sleeping varies depending on the species of fly, but ultimately they prefer somewhere warm. Fruit flies will sleep in temperatures around 80 degrees Fahrenheit, while some other breeds prefer the colder air at 60 degrees. They will not select a location that is too hot or cold but instead, go for somewhere with an acceptable temperature for their species.

Do flies sleep?
Credit istockphoto.com/Roger Thornby

How Do Flies Sleep?

For a fly, sleep is an active process. They have been known to take what we would consider a ‘power nap’ during the day while just sitting on a wall. On a biological level, flies have a need for sleep that is similar to ours.

They will sleep in different positions during their rest, some flies choose to sleep on their backs with their feet in the air. Others may adopt a more natural sleeping position by lying on their side or resting their head down on something like a leaf or wall.

Most flies will lower themselves to the ground and tuck one or both of their wings away under their body. This is known as wing-folding behavior. If they are disturbed during this time it can be quite startling as they fly around erratically or even start flying straight toward you if you are standing in close proximity.

Do Flies Sleep with Their Eyes Open?

Yes, flies have no eyelids and therefore keep their eyes open while sleeping. To keep their eyes clean, flies use their feet to clean them continually.

Why Doesn’t A Sleeping Fly Fall From The Ceiling?

Flies can sleep upside down attached to a ceiling because they have tiny adhesive glands on their feet, which secrete droplets of substance. The fly has enough glue on it to allow it to pull off the foot when needed. Its tiny size aids in the holding of even a light layer of material.

What Do Flies Dream About?

It has not yet been determined if flies experience dreams like humans, but there is certainly the possibility. We still do not know what they dream about or if these dreams are experienced in a way that is similar to ours. Studies have been carried out by The University of Queensland showing that a fly has the same sleep behavior as humans with different activity levels during sleep; cycling back and forth through phases of deep sleep and a ‘wake-like’ sleep (where the brain is extremely active and dreaming, also known as ‘REM sleep’).

Even though flies have relatively small brains, their mental activities are comparable to those of humans.

Do Flies Have Nightmares?

There is no evidence that flies experience nightmares, but they do have the ability to experience and see what we consider to be a nightmare: an image of something that causes fear or stress. 

How Do We Know A Fly Is Asleep?

Flies do not have eyelids, so you can’t watch for a drooping eyelid like with humans and other animals. Flies generally don’t take a conventional sleeping posture. You can’t wait until they curl up somewhere to know they are asleep – flies don’t have a typical sleeping position. If a fly is standing still and not moving, it may be sleeping or quietly awake thinking about its next meal.

The way in which they sleep is similar to us, but they also share another similarity with humans that may be even more strange. It has been observed that when flies are sleeping, they are capable of entering REM within 90 seconds of falling asleep.

When a fly sleeps, it is aware of its surroundings and can awaken quickly if threatened or moved. During REM (rapid eye movement) some flies have been known to twitch their eyes rapidly as if watching images that we cannot see. For a fly, during REM it is as if they are watching a movie and devoting all their attention to the screen.

How Long Do Flies Sleep For?

Flies sleep in different ways depending on their life stage. Adult flies tend to sleep around 13 hours per day, while for larvae it is closer to 20 hours.

The adult fly sleeps most during the night, while larvae (similar to human babies) sleep more during the day. The exact duration of a fly’s sleep is down to its age and the time of day, as well as environmental factors such as temperature. In general, they need to rest more during colder periods of the year.

Do Flies Only Sleep in the Dark?

Interestingly, it is known that flies will still sleep during the day – but only if they are sleeping in a dark place. Flies like humans and other animals need to sleep when it is dark and quiet.

Since darkness enables them to shut down their senses more than those of an average fly, this can be seen as a form of protection. Being able to rest in this way is clearly crucial for their survival and may allow them to recover from strenuous activity during the day or prepare themselves for evening hunting.

Do Flies Fly in The Dark?

Yes. Flies can fly just as well in the dark as they do at other times, but the process is slower and less precise. They are capable of compensating for not seeing very well by using their sense of smell to help them find a mate or food source.

Final Words

So there you have it – flies do sleep and are very much similar to humans in that they just want some regular rest to keep their brain functioning ok.

Next time you see an idle fly in your home, it may not be dead but just sleeping. Maybe decide on moving this tired little friend outside whilst he is inactive and not flying about your home like a pest!

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