A Global Hotspot for Hirudinea
The Kanneliya-Dediyagala-Nakiyadeniya (KDN) forest complex, a humid lowland rainforest, is a global hotspot for biodiversity. Designated a Biosphere Reserve by UNESCO in 2004, this area is one of the most floristically diverse forests in South Asia. But beneath the canopy, in the damp leaf litter, lives a specific and concentrated form of biodiversity: the world's highest known diversity of terrestrial blood-feeding leeches.
These invertebrates belong to the phylum Annelida, the same group as earthworms. The family Haemadipsidae, or jawed land leeches, is particularly abundant here. Species such as Haemadipsa sylvestris and Haemadipsa zeylanica are common throughout the wet zones of Sri Lanka. The damp and shaded environment of Kanneliya provides the perfect habitat for these animals, which are vulnerable to drying out. The forest complex covers over 10,000 hectares and is the watershed for two major rivers, the Gin and Nilwala, ensuring the humidity remains high year-round. This stable, wet environment has allowed for the evolution and survival of numerous distinct species.
Nature's Phlebotomists
The variety of leeches in Kanneliya is the number of species, but in their feeding specializations. This is a classic example of niche partitioning, where different species evolve to use different resources, thereby avoiding direct competition. Some leech species in these forests have adapted to feed on specific types of animals. They detect hosts through vibrations in the ground, changes in temperature, and chemical signals like carbon dioxide.
This specialization makes leeches unintentional biodiversity surveyors. Scientists have developed a method using invertebrate-derived DNA (iDNA) to identify the animals living in a forest. Blood preserved in a leech's gut can be genetically sequenced, revealing its most recent host. DNA can remain identifiable for at least four months after a leech has fed. A single survey collecting leeches can identify dozens of mammal species, including rare and elusive ones that are seldom seen or captured on camera traps. Studies analyzing the gut contents of Haemadipsa leeches have revealed the DNA of a wide range of animals, from bats and birds to large mammals like wild boar and serow, a type of goat-antelope. In Kanneliya, this technique is a powerful, non-invasive tool for monitoring the health of its diverse mammal populations, which include 86 known species.