This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The repulsive slug-like larvae are frequently seen on the foliage of Pear and Cherry. They are bottle green in colour and covered with a slimy matter above; beneath they are paler, and the anterior region of the body is swollen, the head being more or less sunk into it. They have six jointed legs in front and seven pairs of sucker feet, and when mature change to dry-skinned yellowish larva?. Their final stage reaches 1/2 in. in length. The Slugworms feed upon the upper side of the leaves, but leave the under epidermis intact, thus skeletonizing the foliage. When mature, the larvae fall to the ground and pupate in earthen cocoons.
The female Sawfly is black and about 1/2 in. across the wings; the first larvae appear early in June. There may be three broods, and larvae have been found as late as the end of October. The winter is passed in the soil in the larval stage in a cocoon of silk and earth. When they occur in numbers early in the season they do most harm, but even when late they may destroy so much foliage that the ripening of the wood is checked.
Treatment is best carried out by spraying the trees with arsenate of lead. Dusting; with fine lime has also met with success. In gardens the surface soil may be removed to a depth of 3 in., and burnt, in winter.