Once they enter the bottle through the mouth, they'll be unable to escape and will eventually drown in the soapy water below.

Soda bottles can be particularly useful ... trap’s effectiveness in catching unwanted flies. Making a homemade fly trap ...

Plastic bottle fly trap A trap made from any discarded plastic cool drink bottle is easy to make and is an effective trap for houseflies which can be reused as needed. In contrast to the fly ...