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What Are the Stages of Metamorphosis for a Leech?

Leeches are a type of segmented worm that can be found on land, fresh water and salt water. There are various types of leeches that feed, grow and reproduce in different ways. All leech types however have three life stages: egg, adolescence and adulthood. The leech metamorphoses through each stage until it has reached sexual maturity and is able to reproduce on its own.

Reproduction
- All leeches, like earthworms, are hermaphrodites, meaning that each leech is able to provide both the sperm and the egg. Leeches, however, do reproduce in couples, with one leech providing the sperm and the other leech providing the egg. As the leeches intertwine, the leech providing the sperm releases the sperm sack onto the egg-providing where it attaches and fertilizes the eggs. Depending on the type of leech, the time between the laying of the eggs and fertilization can last up to nine months.
Egg Stage
- Once the eggs have been fertilized, the fertilized leech will build a cocoon to lay the eggs. This is the first stage of the leech's life cycle. A leech bearing fertilized eggs will secrete a cocoon from its glands that fully encases the body of the leech. Once the cocoon has been secreted, it will deposit the eggs and extricate itself from the cocoon. The eggs are then protected by the egg laying parent until they are ready to hatch. Incubation of the eggs, as well as type and location of the cocoon, varies by leech species.
Adolescent Stage
- When the eggs hatch, the adolescent leeches break free from their cocoon and attach themselves to the egg-laying leech's body. During this stage of metamorphosis, the adolescent leech appears to be a smaller version of the parent leech. Unlike earthworms, the adolescent leeches do not develop additional segments, and grow by increasing the size of their segments. While the leech is in its adolescent stage it is unable to feed or defend itself, relying exclusively on the parent leech to care for it and protect it.
Adulthood
- Adulthood is reached when the adolescent leech has grown close to the size of its parent and it is able to exist without being attached to it. When an adolescent leech can no longer be supported or protected by its parent, it releases from its body and quickly attaches to another host to rely on for food and protection. Another characteristic of this stage of leech metamorphosis is that they reach sexual maturity and are able to reproduce with other leeches, beginning the life cycle over again.

Animals & Science