As the fruit Slugworm name suggests, this sawfly larvae pest looks halfway between a slug and a worm - Even leech-like. It feeds upon the upper surface of leaves from a wide range of fruit trees and ornamentals, such as apples, pears, plums, Cherries, Crataegus and Sorbus varieties.
Damage normally becomes visible from June until October (Leaf fall) and is apparent with the lace like skeleton or brown patches often left behind.
The larva of a sawfly (Caliroa sp.) species feeding on and skeletonising a Hawthorn leaf.
Fruit Slugworms are actually pale yellow, but are covered with a black slime. Spray with a contact spray such as Bifenthrin if damage become noticeable - alternatively an organic fatty Acid spray will do the trick. Repeat applications my be needed as there can be several generations of Fruit slugworms in a single season.