Agro - Leeches

Feeding and Diet
by: Leeches - Australia Museum

Most leeches are sanguivorous, that is they feed as blood sucking parasites on preferred hosts. If the preferred food is not available most leeches will feed on other classes of host.

Some feed on the blood of humans and other mammals, while others parasitise fish, frogs, turtles or birds. Some leeches will even take a meal from other sanguivorous leeches which may die after the attack.

Sanguivorous leeches can ingest several times their own weight in blood at one meal. After feeding the leech retires to a dark spot to digest its meal.

Digestion is slow and this enables the leech to survive during very long fasting periods (up to several months).

Leeches are grouped according to the different ways they feed.

One group (the jawed leeches or Gnatbobdellida) have jaws armed with teeth with which they bite the host. The blood is prevented from clotting by production of a non-enzymatic secretion called hirudin. The land leech commonly encountered by bushwalkers is included in this group.

A second group (the jawless leeches or Rhyncobdellida) insert a needle-like protrusion called a proboscis into the body of the host and secrete an enzyme, hemetin which dissolves clots once they have formed. Leeches which live on body fluids of worms and small freshwater snails possess such an apparatus.

A third group, (the worm leeches or Pharyngobdellida) have no jaws or teeth and swallow the prey whole. Its food consists of small invertebrates.