This is a family of small to medium sized flies. The members of this family deposit their eggs near snails. The larvae eat the snail. This means that the members of this family are useful in biological pest control. They are bred to reduce the number of snails in farming. But they are also the living proof of how complicated matters like these can become. The flies don't distinguish between noxious snails and slugs and useful ones. How could they? So what is a blessing for one branch of agriculture is a pest for the other, namely the farmers that breed edible snails. Tetanocera elata looks like a Dung Fly and is often mistaken for one.