Penthaleus major, known generally as the winter grain mite or blue oat mite, is a species of earth mite in the family Penthaleidae. They are black or dark blue in color and are widespread across the world. They are commonly found on oats and in pastures and spend most of their time on the surface of soil, and are occasionally found on wheat, barley, peas, lentil and lucerne, and seldom on canola.

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