The molecular detection of slow worm (Anguis fragilis) predation on slugs

Abstract: Slow worm (Anguis fragilis) numbers are in decline due to habitat loss, modificationand fragmentation through agricultural intensification and urban development. While it is knownthat slugs are a significant component of slow worm diet, slug species, and patterns of predationon them, have not been studied before due to inherent difficulties of determining slug identitythrough traditional methods of dietary analysis. In this study, a non-invasive molecular approachwas taken to detect slow worm predation on Deroceras reticulatum and Arion species, majorpests of agriculture, allotments and gardens. Slug DNA was detected in slow worm faecescollected each month between April-September over two years from sites in Dorset and SouthGlamorgan. Relationships between the consumption of slugs and slow worm sex, maturity stage,snout-vent length and weight along with month, site, rainfall and temperature were assessed bygeneralized linear models (GLM). Predation on slugs was high, with 45% of slow worms (N = 400) found to have eaten them (22% D. reticulatum and 30% Arion). Predation on bothD. reticulatum and Arion was significantly affected by month, probably following changes in theabundance / availability of slugs, with D. reticulatum predation also found to be positivelycorrelated with rainfall. In addition, predation on both D. reticulatum and Arion was positivelycorrelated with air temperature, when there is a greater abundance of slugs and when slow wormsare more active. Furthermore, a sex bias was found in predation on Arion, with female slowworms more likely to have consumed them in April, May and September. This may reflectdifferent nutritional requirements of males and females. On a domestic scale, slow worms couldbe encouraged to help suppress slug numbers on allotments and in gardens by the provision ofareas of rough grass and refugia (large stones / sheets of tin / carpet).