Do flies feel pain? Yes, but in what way?

Do you assume, as I did, that flies do not feel pain, that you can kill them mercilessly and chuck their carcasses out of the window when they come into your home? Are you happy to kill flies? To rid yourself of that irritating buzzing noise in your living room? And when they starve to death in your home because they become trapped, are you pleased?

You might like to adjust your opinion if you are an animal advocate. This is because a study concluded that insects can experience chronic pain. For example, injured fruit flies experience nerve pain after healing. The pain that they feel is called ‘nociception’. I can barely pronounce it but the guy in the video below can and he talks about it. The study says that nociception “is a protective mechanism that mediates behavioural responses to a range of potentially damaging stimulant including noxious temperature, chemicals, and mechanical stimulation”.

Fly died of starvation and lack of water in my bathroom
Fly died of starvation and lack of water in my bathroom. Photo: MikeB

What this means is that flies react to situations which can damage them. Flies have a nervous system. And pain lingers throughout the fly’s short life (28 days for the housefly) after the injury has healed. They discovered this because they injured one leg of a group of fruit flies which can cause chronic nerve pain. The injury healed and they placed the flies in a hot room. The flies with injured legs tried to leave the room because the higher temperatures caused dicomfort? Their legs had become hypersensitive and they tried to protect themselves against the “pain”.

Note: This is an embedded video from another website. Sometimes they are deleted at source or the video is turned into a link which stops it working here. I have no control over this.

Flies do have a kind of nervous system which includes a brain and spinal cord of sorts. But if you read other articles about insects feeling pain you see a range of responses with some experts not quite so convinced.

For example, on, about 10 years ago, a UC Davis entomologist and doctoral candidate, Matan Shelomi, expressed his opinion on this topic and he said that insects “don’t feel pain, but may feel irritation and probably can sense if they are damaged. Even so they certainly cannot suffer because they don’t have emotions”.

That last sentence I think is important because the nervous system and the brain can signal pain but whether the insect feels pain is how they interpret that signal. The argument by this man is that if they don’t have emotions – and I think we can agree the flies don’t have emotions – their reaction to the ‘pain’ signal will be different to humans and one which might not cause discomfort. It might be a signal to tell the flies that they need to do something to assist in their survival. That’s my interpretation.

But do we need emotions in order to experience pain? Right now, I don’t know the answer to that question. But if we don’t need emotions to feel pain the fact that flies do not experience emotions will not be a barrier to them feeling chronic pain.

The bottom line is that we don’t know how flies experience pain and whether they genuinely feel pain as we know it. But it is pretty clear that we can’t assume that they are completely unfeeling automatons which we can smash into the window pane with a towel.

The reason why bugs like flies lie on their back when they are dying or dead is because they simply don’t have the ability to get up. And we see this a lot when flies starve to death and die due to a lack of water when they are trapped inside a home. Apparently, it takes about two or three days for a fly to die in this way. The question is whether they suffered pain during the starvation process and through two days of a lack of water. If they feel pain, they should feel some discomfort if they starve to death.

Finally, a lot of people allow their domestic cat companion to attack and kill flies. Does the fly feel pain under these circumstances before they die? They don’t feel emotions therefore they don’t feel fear. My conclusion is that they know when they are injured through signals from their nervous system but don’t know that they are dying.

Below are some more pages on insects.

Two useful tags. Click either to see the articles: Speciesism - 'them and us' | Cruelty - always shameful
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Post Category: Insects