This linear mine gradually widens into a blotch mine and becomes more noticeable as the larvae change from sap feeders to tissue feeders.
Fresh mines are sometimes whitish and very noticeable.
They are often referred to as frog eye . Blotch mines near the leaf edge are often a little drawn or puckered and thus tent-like in appearance. Larvae pupate in flat, oval cocoons of densely woven silk within the upper blotch mine. The pupa wriggles free of the cocoon and breaks through the upper leaf surface. There are three generations per year.