The leaves, twigs and fruits of pears, apples and cherries are sometimes badly discolored by the growth of the fungus Fumago vagans in the honey dew secreted by lice. The fungus is dark and its development is so extensive that it presents a very conspicuous black or sooty mold aspect. Since F. vagans lives in the honey dew, it is most prevalent in epidemics of the pear psylla and apple louse. The fungus itself needs to cause no fear; it may be eliminated by controlling the above - named insects.