Jaw width and body weight show a significant correlation for each of three slugs examined – Deroceras reticulatum, Arion hortensis and Milax budapestensis. The jaws of slugs and snails resist digestion in the gut of bird and mammal predators. Under certain conditions, the jaw of D. reticulatum can be recognized and the size of slugs eaten may be estimated from jaws recovered from the gut of a predator, using a regression line. This technique has been used to study predation of slugs by starlings, hedgehogs, shrews and moles. Since slugs are agricultural pests, the technique may he useful for assessing the effect of vertebrate predation on slug populations.