When leeches mate, the leech playing the male role (leeches are hermaphrodites and can assume either sex) clings to the body of the female and deposits a sac of sperm on her skin. This sac produces a strong, flesh-deteriorating enzyme that eats a hole through the female’s skin and fertilizes the eggs within her body.

Wolves have only one breeding season per year – in the winter. They have their puppies in late April or early May. They have their puppies in an underground hole, or den. There are usually four to six puppies in a litter. The puppies grow up fast and are their adult size by the end of their first winter. They are grown up by the time they are two years old.