Which Do Flies Prefer: Beer or Sugar Water?

Although flies are known for being attracted to sweet things, they actually prefer beer over sugar water — even beer that has a relatively low sugar content, such as pale ale. This is because they are more attracted to a molecule called glycerol that is produced by yeast as beer ferments. Besides beer, glycerol is found in a wide variety of things, including cosmetics, some medications and antifreeze.

More facts about flies and glycerol:

• Researchers hope to use the information they find out about how flies recognize compounds such as glycerol to understand more about how taste works in humans. Having a better understanding of how flies chemically experience the world also can help with the development of pesticides.


• Houseflies' mouths absorb food like a sponge, so they soak up the food first and then suction it into their bodies. They can eat dry food by either spitting or throwing up on it until their mouth can soak it up.


• Flies like to eat rotten or decaying food because it's generally more liquified. It also usually smells stronger, so it's easier to find.

Frequently Asked Questions

Do flies have a preference between beer and sugar water?

Flies are generally attracted to sugary substances due to their high energy content. However, they are also drawn to the fermentation odors in beer, which mimic the scent of decaying organic matter, a natural food source for them. Studies have shown that flies can be more attracted to alcoholic beverages like beer over sugar water due to these complex olfactory cues.

What component in beer attracts flies?

Beer contains ethanol, a byproduct of fermentation, which is a signal for potential food sources for flies. The combination of ethanol and other organic compounds in beer can be irresistible to flies as it indicates decomposing material, which is a staple in their diet. The carbonation and sugars present in beer also contribute to its attractiveness.

Is sugar water a reliable bait for trapping flies?

Sugar water is an effective bait for trapping flies because it offers a high-energy food source. Flies are equipped with taste receptors that are highly sensitive to sweet substances, making sugar water an attractive option for luring them into traps. However, adding a little vinegar or dish soap can increase efficacy by breaking the water's surface tension, causing flies to sink.

Can the preference of flies for beer or sugar water be used in pest control?

Yes, the preference of flies for beer or sugar water can be leveraged in pest control strategies. By using these liquids as bait in traps, one can effectively lure and capture flies. Commercially available fly traps often use similar principles, incorporating attractants that mimic the scents of fermenting or sweet substances to draw flies in.

Does the type of beer matter when attracting flies?

The type of beer can influence its attractiveness to flies. Darker beers with stronger aromas may attract more flies due to their higher levels of fermentation byproducts and complex scents. However, any type of beer can be effective because flies are generally attracted to the ethanol and fermentation odors present in all alcoholic beverages.

Are certain species of flies more attracted to beer than others?

Different species of flies may exhibit varying preferences for beer. For instance, fruit flies (Drosophila spp.) are particularly drawn to fermented substances, including beer, due to their natural attraction to rotting fruit. Other fly species, such as houseflies, may be less discriminating and attracted to a range of sweet and fermented odors.