Worms and leeches are members of the phylum Annelida. Annelids can be distinguished by:

• long cylindrical body of many similar segments
• no limbs
• no antennae
• no obvious head

Worms and leeches are the only terrestrial members of this group.

Earthworms prefer wetter areas and often have a significant effect on soil by breaking down organic material and aerating soil. The current origin of almost all earthworms in Canada is thought to be from introductions from Europe. Almost all native Canadian earthworms were lost during the last ice age.

Leeches are segmented annelids with suckers on each end of its body. Despite what many people may think, very few species of leeches actually feed on humans; most leeches feed on decomposing bodies, amphibians, reptiles, waterfowl, fish, and other mammals. There are an estimated 45 species of leeches in Canada.