House flies are gray, approximately 6 mm (1/4 inch) long, with four dark longitudinal stripes on top of the thorax, or middle body region. The mouth parts of the house fly are adapted for sponging up liquids. They cannot bite. Flies ingest only liquid food; they feed on solid food by regurgitating saliva onto it. The saliva liquefies the solid material, which is then sponged up with the proboscis. They require water since they continually salivate. Fly specks seen on surfaces visited by house flies are the excreted wastes.