Complex sentence: Calling it a "flea" simply is a reference to its jumping ability and its small size; as Collembola go, it is a fairly large species, commonly up to 3 mm in length.
Split into simpler sentences: Calling it a "flea" simply is a reference to its jumping ability and its small size. As Collembola go, it is a fairly large species, commonly up to about 3 mm in length.