The chemosensory ability of the predatory leech Whitmania laevis (Arhynchobdellida: Haemopidae) for prey searching

Although prey-detecting and searching abilities of predatory leeches of rhynchobdellid or the Erpobdelliformes of arhynchobdellid species have been studied in the past, hirudiniformes leeches are rarely mentioned. In this study, we investigated the chemosensory ability for prey-detecting and searching in Whitmania laevis, a hirudiniformes species that mainly preys on freshwater snails, and examined if such ability aided in their prey selection. Five sympatric snail species, i.e., apple snail Pomacea canaliculata, thiarid snail Thiara tuberculata, viviparid snail Sinotaia quadrata, ear pond snail Radix auricularia swinhoei and tadpole snail Physa acuta were used as prey. Our results showed that W. laevis has the chemosensory ability to detect the waterborne odors of snails. However, they follow the snails by their mucus trails, and not by the odor that the snails leave in the water. Of these five snail species, W. laevis only followed the trails of the thiarid snails, ear pond snails and tadpole snails, and did not show a different response to the trails produced by snails of different sizes. Our results suggest that W. laevis can use waterborne odors to detect the existence of prey. They rely on mucus trails to follow their preferred prey, but do not distinguish between snails of a preferred size by their mucus trails. In addition, when following the trail of a preferred snail, W. laevis exhibits a newly described searching behavior, i.e., head tapping, and may use it to locate a snail trail and increase its probability of finding the trail-laying snail nearby.