Why are werewolves and vampires enemies?

Mythologically speaking, they never were enemies. Back in the era of the Universal monster movies in the 1930s,1940s, and 1950s the movie studios needed a supernatural adversary to fight Dracula on his own terms, so they merged the continuities of the Dracula movies starring Bela Lugosi with the Wolfman movies starring Lon Chaney. This idea eventually incorporated the Frankenstein's Monster as well as the Invisible Man, until the idea reached its comedic zenith with "Abbott and Costello meet Dracula".

In the early 1990's there was a role-playing game by White Wolf Inc. called Vampire: the Masquerade in which the players took on the roles of the vampires as they struggled to retain their humanity in a world of darkness. One of the prime adversaries to the vampire characters were the Garou, or werewolves, who were champions of Gaia, or the earth and saw the vampires as corrupt abominations. Eventually they released the game Werewolf: the Apocalypse, in which players got to play the Garou against vampiric enemies.

Then came the Underworld movies, and Van Helsing (which was a complete homage to the old Universal movies of the 40's) in which the two "races" were at war once again. Mythologically it was believed in Greece that a werewolf would become a vampire upon death anyway, so they two were linked, but never in an antagonistic manner.

After that came television shows like Kindred: the Embraced (based on Vampire: the Masquerade), Being Human, Buffy, Angel, and now we have the Twilight movies that continue to posit the completely non-mythological "rivalry" between these two myths.

It makes for better movies and books. The early Vampire movies would have the Vampire change to smoke and get out of any tight squeeze.

differences and territory, Vampires are suppose to be very territorial creatures.. and needless to say so are wolves. This issue is only intensified because either party doesn't think that the others are worthy to be considered with the same respect. So vampires would never seen warewolfs as equal because one they are on the vampire proclaimed land and different. and vice versa.

Its all comes down to prejudice and land actually...

Invasion of each others territorial rights and claims is about the only logic for this in books and movies.

It depends on the writer of the particular Vampire/Werewolf story.Although there are actually some movies that show them as allies and actually in the original folklore one of the ways to become a vampire after death was by being a werewolf in life.

For the same reason orcs don't like elves - that's the way the stories are written.

That witch Stephanie Meyer made them.

How would you feel if you were a werewolf and your dead food wakes up and tries to kill you?