Leeches add interesting new angle for evolutionary biologists to consider when explaining how parental care has evolved

When it comes to parenting, leeches are quite accomplished. Although some leeches abandon their young at birth, a Monash University study of the Australian leech species, Helobdella papillornata, has found that it broods its eggs and young on its body for several weeks and captures food for its offspring.

Evolutionary biologist Dr Fred Govedich from the School of Biological Sciences has been studying the parenting behaviour of leeches in an attempt to gain a better understanding of the evolution of parental care in animals.

"Although the word 'leech' is often considered synonymous with selfishness and exploitation, many leeches are devoted parents," Dr Govedich said.

"After fertilisation, sexually mature leeches produce cocoons containing eggs. Helobdella attaches this cocoon, which contains 30 to 40 eggs, to its body. Once the eggs hatch, the juveniles attach themselves to the parent, remaining there for five to six weeks."

Helobdella is a member of the glossiphoniid family of leeches. It is a tan colour, grows up to two centimetres long and is typically found in ponds or bodies of slow-moving water.

"Leeches are hermaphrodites, but Helobdella displays parental behaviours that are associated with birds and mammals, which have separate sexes," Dr Govedich said.

"This particular leech cares for its eggs by providing ventilation and defending them from predators such as fish. Then, once the young are hatched and attached to the body, the parent captures snails and other suitable foods for them to eat as well as transporting them to areas where there is plenty of oxygen and lots of prey for the young to feed on once they leave the parent."

Dr Govedich has also found that Helobdella is a social leech. It will aggregate in groups of up to 50 other leeches and will also provide food to the young of other leech species.

"In many ways, the parenting of this leech is similar to that of some birds and mammals. In terms of the evolution of parental care, it is fascinating that an invertebrate is displaying vertebrate-like parenting.

"These findings with respect to Helobdella introduce an interesting new angle for evolutionary biologists to consider when attempting to explain how parental care has evolved."