Greater Snail Leech
Glossiphonia complanata
The Greater Snail Leech is a common freshwater leech with a flattened, oval body shape. It reaches a body length of up to 4 cm and features characteristic longitudinal stripes and six rows of papillae on its dorsal side. Its coloration typically ranges from yellowish-brown to greenish-grey. A defining feature is the presence of three pairs of eyes at the anterior end, arranged in two parallel rows.
Details
Identification
Three pairs of eyes in two longitudinal rows, six longitudinal rows of small papillae, flat and broad body, firm posterior sucker.
Social behavior
Predominantly solitary, but exhibits highly developed parental care behavior towards its offspring.
Diet
Specializes in feeding on freshwater snails (e.g., pond snails) by inserting its proboscis into the soft body and sucking it out. Occasionally, other invertebrates such as worms or insect larvae are consumed.
Hunting strategy
Lurks on the underside of stones or leaves; uses chemoreceptors to follow the mucus trails of snails.
Spawning substrate
Eggs are laid in cocoons on stones, plants, or the bottom of the water body.
Overwintering
Overwinters in sediment, under stones, or in deep water to avoid freezing.
Ecology
Ecological role
Regulator of snail populations in standing and flowing waters.
Natural predators
Fish, predatory insect larvae (e.g., dragonfly larvae), waterfowl.
Competitor species
Other leech species of the Glossiphoniidae family as well as predatory water beetles.
Ecosystem service
Contributes to biodiversity and the control of gastropod populations.
Threats
Severe chemical pollution of water bodies, habitat loss through riverbank reinforcement, and drying up of small ponds.
Scientific profile
Profile
Distinguishing features
Possesses exactly three pairs of eyes arranged in two parallel longitudinal rows (distinction from Alboglossiphonia). The firm body consistency prevents significant stretching, which is common in other leeches. Six rows of dorsal papillae are usually clearly visible.
Diet
Mainly freshwater snails (e.g., Bithynia, Lymnaea, Planorbis), but also Oligochaeta (worms) and chironomid larvae.
Reproduction
Hermaphroditic. Mating occurs via the transfer of spermatophores. Intensive parental care takes place: eggs are carried in cocoons on the ventral side. After hatching, the young attach themselves with their posterior sucker to the parent's belly and are transported to food sources.
Role in food web
Secondary consumer; plays an important role in regulating snail populations within benthic communities.
Protection & threats
Main threats
River engineering and bank stabilization (loss of hard substrates), excessive siltation of the riverbed, pesticide input.
Conservation measures
Preservation and restoration of near-natural water structures, promotion of connectivity, reduction of fine sediment input to protect colonization areas.