Know your leech, a guide to 11 sp. of British freshwater leeches

British freshwater leeches are most easily identified by examining the head shape and eye arrangement, lengths are in mm of fully grown leeches at rest. There are 16 British freshwater species.
Ryncobdellidae - these have a proboscis, colourless blood and no jaw.
Species
Appearance
Eyes
Behaviour
Length
Head
Protoclepsis tasselata Olive green, brown, transparent. In large individuals 6 rows of yellow spots down the dorsal surface. 8 in 4 pairs Very active. Feeds on ducks and other water birds entering the nasal cavities and throat. Can lead to death of victim. Egg capsule carried by adult. Young (up to 200 at a time) also carried by adult. up to 60 mm
Protoclepsis tasselata, freshwater leech
Pisicola geometra (common fish leech) Green or brown/red. 8 rows of white spots. Long and narrow. Both suckers large. 2 pairs Very active. Attacks fish. Eggs laid inside brown cocoons 15 mm long and attached to stones etc. 20 - 50 Pisicola geometra
Glossosiphonia complanata Dark green/brown. 2 rows of cream and brown coloured spots running down either side of a dorsal mid-line. Narrow head. 2 or 3 pairs Curls into a ball when disturbed. Feeds on freshwater snails and Chironomid larvae. Eggs are laid an a transparent cocoon attached to a solid object. Found in stagnant pools and running water. 30
Glossosiphonia complanata
Glossosiphonia heteroclita Amber yellow. Dorsal surface may have small black/brown spots. Long oval with narrow head. 3 pairs Feeds on water snails. Up to 60 eggs laid June/July, attached to the ventral surface of the adult. Found in slow, running or stagnant water. 10 - 15
Glossosiphonia heteroclita
Helobdella stagnalis Transparent green/grey/pink. Dorsal surface may have black speckles. Long oval body, narrow head. 1 pair Feeds on freshwater snails, Chironomid larvae, annelids. Eggs carried on ventral surface of parent. Found in ponds and slow moving streams. 10
Helobdella stagnalis
Hemiclepsis marginata (fish leech) Colour varies. 7 yellow spots down dorsal surface. Rounded head. 2 pairs feeds on fish. Eggs attached to ventral surface of adult. 16 - 18
Hemiclepsis marginata
Haemopsis sanguisuga (horse leech) Black/green/olive brown. Both surfaces have black spots. Jaws have 11 - 18 pairs of teeth, but cannot pierce human skin. See drawing above. 5 pairs Feeds on earthworms, snails, insect larvae, tadpoles, dead animals and other horse leeches. Also unlike other leeches it swallows its prey whole. Found in mud in ponds, or on stones in streams. 25 - 35, but can stretch to 150
Haemopsis sanguisuga, horse leech
Hirudo medicinalis (medicinal leech) Olive green with red, yellow, orange and black lines. See the photograph above right. Jaws have many teeth capable of piercing human skin. 5 pairs Cocoons are laid in damp soil. For more details see above right. 30 - 35, but can stretch to 200.
Hirudo medicinalis, medical leech
Herpobdella octoculata Dark brown, also yellow and reddish brown. Black marks. Body long and narrow. 4 pairs Eats small worms such as Tubifex, and planarians. Eggs laid in dark brown transparent cocoons attached at both ends to a solid object. Found in running and stagnant water. 30 - 40
Herpobdella octoculata
Herpobdella atomaria Green/brown with a paler ventral surface. Red/yellow spots and a black pattern. Resembles H. octoculata. 4 pairs Food as H. octoculata. Egg cocoons brown transparent and attached to solid objects. Found in running and stagnant water.  
Herpobdella atomaria
Trocheta subviridis (amphibious leech) Grey/green or reddish with paler ventral surface. 2 brown dorsal lines. Long, worm-like shape. 4 pairs Feeds on earthworms and insect larvae. Will leave water to search for food. Lays flat, brown elliptical egg capsules attached to solid objects. 80 - 100
Trocheta subviridis