What are flies doing? Why do they want to land on humans?



Summer is here and my area seems to have an excess of flies. I can’t go on a hike without them buzzing all around me and trying to land on me. What do they want?? Sweat? There is plenty of water elsewhere. Can someone explain so I can figure out a way to dispel these demons?

In: Biology




I think that they’re attracted to sweat. That’s why there aren’t any flies on prince Andrew

Moreover, why are some black flies blood thirsty biting machines while others are not?

In Australia in the dryer parts they want to drink fron the corners of your eyes and mouth there is a small amount of moisture there they can drink… they also want your sweat

ELY5: Humans are an attractive thing to land on. Flies like to eat dead skin cells and drink sweat. On a hot day, the carbon dioxide you exhale and the sweat you let out is attractive to flies. They also need a place to land and rest. Why not land on a human that is creating sweat. It’s like a vein of ore.

Things that work for me to keep bugs away:

Liquid garlic: I pour a small amount into my hand, just enough to make my hand wet. I smear it behind my neck, on my ankles, and on my forehead. I also put a dot on my chest on whatever clothes I am wearing. It smells pretty much like garlic bread, and all insects give me a wide berth. Liquid garlic is one of the reasons that mosquitos are not present at Disneyworld despite being situated in a swampland.

Edit to address some comments at once:

Context: I’m an arborist among other things, once I get high up in the tree they stay away but while I’m down on the ground I like to keep the bugs away. This has been the best method so far. I’m usually pretty bug free but often get called out to an area that is not maintained and has a lot of standing water. This means baby mosquitos that are too dumb to be sneaky. They get killed very quickly by natural selection but if you are near them this means they land on your ear or your eyelid and immediately put their proboscis into you and inject upon landing. They just landed and are already dead, but now you have a mosquito bite in the dumbest place ever….your eyelid. The liquid garlic, though at a level that is not even noticeable by humans, is like tear gas for bugs.

I did mean “small amount” when I said “just enough to make my hand wet.” That is the most I’ve ever used for very extreme situations that would normally have you covered in bug bites within a minute. For normal situations I just put a small dot of it on my work shirt and they stay out of my face. The dot on the work shirt is not enough to be noticed by myself or other people . When I put it on the back of my neck, forehead, hands, and ankles, it smells like an Italian restaurant and makes people hungry. But that is the price I pay for the worst environments. In those environments I clear them out within the first day, but not having bug bites and ticks to worry about is critical. Ticks literally crawl off of me when I put liquid garlic at any entry points like my wrists and ankles, that is it’s own reward.

Funny sidenote, if a mosquito follows me into my vehicle after I’ve washed off and don’t smell like an Italian restaurant, I will just take the lid off the bottle and the mosquito immediately starts looking for an exit. It’s funny to watch and no one likes chasing a bug around their car or house.


Edit: I’m adding my other comments on pest control in here just to keep it all in one place. I hope this helps someone avoid learning the hard way like I did.


On the note of reactive measures, any hard bodied insect dies on contact with soapy water in a squirt bottle. For larger groups like hornet nest I splash them with a cup full of soapy water. The soap is not harmful to plants or animals but for hardbodied insects it breaks up the cells and exoskeleton at a molecular level.

Edit: I’ve had a few comments on effectivity and mechanisms. The following link is a good one, it explains the two reasons it kills bugs on contact, as well as how to make it:



Another proactive measure for homes and gardens:

Diatomaceous earth is something I use for home and garden intruders. It is not a fast death so I would not use it out in the wilds, but it is good for keeping invaders like flea beetles away from your house and garden. Diatoms are a type of algae that happens to dry in a shape that is very spiky. If you mix it with water in a spray bottle or just poor it outside an entry way, any hard-shelled insect that touches it can’t get it off. Imagine when you get a burr stuck to your clothing, except you are an insect and the burs are shaped like needles from a spike strip, and can’t be removed because you don’t have opposable thumbs. The DE kills the insects by drying them out, they get stuck in the joints of the exoskeleton and dry the bug out and it dies of dehydration after 2-3 days. The advantage is that you don’t see a bunch of dead bugs around your plants because the DE makes them leave to find a water source and spend their last days not even thinking about biting your plants or family. Very useful for spraying on window sills or the undersides of plants. The bugs just “get the message” and leave your stuff alone. Although it is a painful way to die, it is a measure that won’t occur unless the bug is trying to pass into your house or munch on your plants. It’s not good for EVERYTHING but has been studied thoroughly and does serve a purpose:

Link: [https://www.pctonline.com/article/pct1213-diatomaceous-earth-study/](https://www.pctonline.com/article/pct1213-diatomaceous-earth-study/)

I’m currently at my Dad’s camp in Northern Vermont. I always look forward to this and then I’m reminded when I exit my vehicle at the camp and I’m immediately chased inside by a swarm of Horseflies. They swarm around my head and continuously try to bite me. I drove my truck through the woods and horseflies were absolutely everywhere. Why do we need these things!?!?!?! Is there a bird species I can get to eat them all.

Have you tried insect repellent?

Flies are dumb. They react only to the smell of stuff they are “programmed” to be interested in – sweat/body odors, carbon dioxide we breathe out, things like that. They follow the smell and arrive at you. They are not even trying to be annoying – when you swat them away, they flee a bit to get away from the immediate threat and then the “fly to the smell” behavior kicks in again, which is why they are so annoying. Same for biting insects like horseflies, except that they react to some additional things like dark colors and body heat.

What I want to know is how do house flies know when I just temporarily opened up my front door for a minute? I mean are they waiting around outside with an eyeball on my door just waiting for the opportunity? Or are there so many of them around at all times (even though I can’t see them anywhere) that somehow there’s always one nearby when I open the door? And like, I was under the impression that they don’t have very good eyesight so I don’t know how a fly that’s twenty or thirty feet away sees me opening the door.

And yet despite all that somehow… I open the garage door or the back door or whatever… And 10 seconds later there’s a big old fly in there.

How do they do it???

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