Nightcrawlers (Lumbricus terrestris) are large worms that have a distinct, dark-colored 'head' end which contains the primitive 'brain' of the animal, and this tends to be the end of the worm that travels 'forward' the most. They are also known as 'dew worms', probably because they are found more commonly on nights when the ground is moist from a dew or rain. The nightcrawler is not native to North America but is a European species that was introduced to the new world with the advent of European settlement. Like most other worms, they are hermaphroditic, having both male and female reproductive organs. Most worms must still mate with another of their species in order to reproduce. When two worms or crawlers mate, they lie alongside one another, and both transfer sperm to each other. Each will lay one or more capsules of eggs from which will emerge one or two fully-formed tiny worms. The familiar thickened 'band' near the front end of most worms is a structure called the clitellum which secretes mucous and other substances that form the capsule containing the fertilized eggs. Ludlow, MA.