Body shape and food habits of South American goo-eater snakes of the genus Sibynomorphus

Abstract

Snakes of the tribe Dipsadini feed mostly on annelids, slugs, and snails. Some species that feed exclusively on snails are able to de-shell their prey prior ingestion. On the basis of dissection of preserved specimens from museums, we report the dietary habits of three species of Sibynomorphus from Brazil. Eighteen to 26% of the snakes had stomach contents, varying from 1-8 items, and the number of prey was not correlated with snake size. Prey mass was positively correlated with snake mass, but relative prey mass decreased with increasing snake size. Prey mass represented less than 5% of the predator mass for all species. Sibynomorphus neuwiedi and S. mikanii only had Veronicellidae slugs in their digestive tract, whereas S. ventrimaculatus also included snails in their diet. Sibynomorphus mikanii ingested most prey rear-first, but there was no difference in direction of prey ingestion by the other two species. Snake morphology differed among species and provided insights into habitat use and feeding habits. Sibynomorphus neuwiedi was the largest species and had the longest tail. Its eyes were also larger than those of S. mikanii, which, together with tail size, suggests more arboreal habits. Sibynomorphus ventrimaculatus had the largest head relatie to the body, which might facilitate ingestion of snails. In summary, the three species of Sibynomporphus are slug specialists. Like other goo-eaters, these snakes feed on very small and low caloric prey, which might require them to feed frequently. This hypothesis is supported by the larger number of prey ingested by these snakes compared to non-goo-eater species of Dipsadini.