The showbiz maximum is that actors should never work with kids or animals, because they’ll be upstaged by both.  Supernatural has broken both halves of this rule several dozen times over, but to great effect.  And for good reason.  Children and animals are often associated with the otherworldly, so their inclusion in the show is logical.  Imagine Supernatural without creepy children.  From the young changelings sucking the life out of their pseudo-parents to the child ghosts of “The Real Ghostbusters”, there have been some memorable scares in small packages.  None was more terrifying than Lilith, smiling with demonic cheeriness through an innocent looking little girl.

Animals in Supernatural: The Good, The Bad, and The Disgusting
“Animals can have a sharp sense of the paranormal.” – Sam in “Skin”


The showbiz maximum is that actors should never work with kids or animals, because they’ll be upstaged by both.  Supernatural has broken both halves of this rule several dozen times over, but to great effect.  And for good reason.  Children and animals are often associated with the otherworldly, so their inclusion in the show is logical.  Imagine Supernatural without creepy children.  From the young changelings sucking the life out of their pseudo-parents to the child ghosts of “The Real Ghostbusters”, there have been some memorable scares in small packages.  None was more terrifying than Lilith, smiling with demonic cheeriness through an innocent looking little girl.
While the twisted events surrounding children have been discussed and debated in a variety of forums, the more subtle, though on occasion more gruesome, roles of animals in the show are not mentioned with the same frequency.  What follows is a look at when animals appear in the show, and the part they play.
A Definition
The first question in writing about animals in Supernatural is to draw the line between animal and monster.  Anything that was once, can transform into, or can communicate in the same manner as a human, is a monster.  No matter how animalistic the behavior of vampires, werewolves, skinwalkers, wendigos, shapeshifters, sirens, rugarus, ghouls, wraiths, changelings, dragons, and fairies, they are not animals.  Part of the horror of these creatures is that they reflect the darkest possibilities of intelligence and human nature.  The term ‘animals’ means those living creatures of non-human aspect, ability, and intelligence.
This is not to say that animals are unintelligent.  Test after test shows that animals are much smarter than traditional outlooks suggest.[1]  And this author has the greatest love and respect for them.  That is the primary reason why the occurrence of animals in Supernatural was chosen as an article topic.
Underrepresented Lifeforms
Aquatic life has not been mentioned in any particular detail – other than a discussion of the Loch Ness Monster being real.  Most of their investigations have occurred in inland locations, other than one ghost ship and one haunted lake, so while Sam and Dean have yet to fight a demonic octopus, there is always hope.  There have been frogs, which are technically amphibians, but are found near water.  One was seen in the episode “Bedtime Stories”, which dealt with fairy tales coming to life; it was likely a reference to the story “The Princess and the Frog”.  And in the episode “The Third Man”, Balthazar used a part of the Staff of Moses to plague an angel serving Raphael with frogs, which crawled out of his throat.
One would expect Sam and Dean’s investigations to unearth more rats.  There were a few rats being eaten in “Family Remains”, and they concoct a fake rat infestation to close a restaurant, but otherwise references to furry vermin are scarce.  Sam and Dean dig up bodies, investigate and squat in ruined structures, and root around in sewers without in countering any signs.  Then there are the motel rooms they rent.  Some of those have to be rat or mouse infested.
And then there are birds and snakes.  The pilot episode had a quick scare with a bird, but considering that Alfred Hitchcock made an entire movie about attacking birds, homages are noticeably absent.  Snakes are a classic movie monster, from “Snakes on a Plane” to Kripke’s fictional “Octocobra”.  On the show, however, the main person to be scared by a snake is Dean, during “Yellow Fever”, and that was a pet.  The only other quick reference was from Ash, who in heaven commented that he was his “congregation’s number one snake handler.”
Vengeful Creepy Crawlies
The most obvious episode in which animals appeared is Season One’s “Bugs”.  Despite the title, a number of invertebrate creatures featured which were not technically ‘bugs’.[2]  Regardless of taxonomy, the creatures caused many a viewer to shudder as they crawled, flew, and chewed their way across screen.  A group of beetles ate one man alive.  Spiders killed a woman in a shower.  Then a horrific number of bees descended on the Winchesters and the family they were protecting.  They survived, no doubt emotionally scarred.
These particular beasts were motivated by a curse to make a patch of land, the site of a slaughter, uninhabitable for one night a year.  This is in keeping with a long tradition in horror that employs insects, arachnids, and vermicullae for shock value, from “Them!” and its giant mutant ants to the “Indiana Jones” franchise to the spiders of “Arachnophobia.”  These scares work so well because a significant percentage of viewers fear this group of animals.  Their appearance is disturbing, with too many legs, too many eyes, and rapid, skittering movements.   Some varieties of spiders and insects have poisonous bites, or cause fatal allergic reactions.  Leeches and mosquitoes feed on human blood.  
Other critters are associated with death and decay.  Decomposers surround bodies both human and animal, eager to feed, be they flies or beetles or worms.  A useful ecological function to be sure, but a disturbing one: one witch on Supernatural avenged herself on an ex-lover with a plate of maggot riddled food and a spell to take the maggots to him.  
Swarms are the most frightening aspect of these creatures.  Millions upon millions of bugs which are individually frightening become a terror when they band together.  The swarm hints at just how many more insects there are than people on earth; the ratio may be as many as 200 million to one.[3]  Picture that cloud of bees coming at you, landing on you.  No wonder some of the more horrible ancient punishments involved placing a victim in the way of a swarm.[4]  That most famous of swarming insects, the locust, had a role in Supernatural’s “The Third Man.”  A boy using a fragment of the Staff of Moses to avenge his brother caused locusts to eat their way out of a man’s skull.  
Animals in Other Magic
The magic in Supernatural often requires animals, or at least animal components.  
Rabbits have been spell victims.  Sam and Dean had to contend with a cursed rabbit’s foot, which had been made years before by a witch who killed the rabbit in a graveyard.  The origin of the rabbit’s foot as a good luck charm is debated,[5] but rabbits have a long association with magicians and magic.  One of the magicians in “Criss Angel is a Douchebag” had one.  The first episode specifically about witches, “Malleus Maleficarum”, had hex bags containing bird bones and rabbit teeth.  Dean got quite a shock when he walked into one witch’s home and found the rabbit that died for the spell.  He felt sorry for the “poor little guy”.  
Lamb’s blood has its uses, too.  To kill a djinn, the brothers used a silver knife dipped in lamb’s blood.  Years later, when Balthazar sent them to an alternate universe, he pulled lamb’s blood from Bobby Singer’s refrigerator to add to other spell components.  If Bobby keeps something like that on hand, then lamb’s blood may have other common uses in the Supernatural universe.  Outside of the show, the blood of the lamb is a well-known Christian metaphor related to redemption and absolution.  In the book of Exodus in the Old Testament, it was lamb’s blood that marked the door posts of those who would be saved from the destroyer sent to kill the firstborn of Egypt.  Lambs were considered an acceptable form of sacrifice.[6]
Both rabbits and lambs are traditional sources of meat.  Rabbits are thought to have been domesticated before 1000 B.C.  As prolific breeders, they were a reliable source of meat for long sea voyages, and were suitable for sport hunting.  During the Middle Ages they were approved for consumption during lent.  The first use of rabbits as pets may have been during the Renaissance,[7] and has since become more common, but rabbits remain a food source for many people.  Sheep are an even older domestic animal, thought to have been tamed by 7000 B.C.[8]  Lambs are sheep under one year of age, and are favored for their tender meat.[9]
The commercial slaughter of rabbits and lambs is an advantage for Sam and Dean, should they ever need the components.  While it appears that witches like to do their own butchering, Sam and Dean do not seem as eager to shed animal blood.  Neither of them is opposed to using the components when necessary, and they are far from vegetarians.  Actually, Dean is the opposite of a vegetarian.  And he doesn’t mind vampires eating cows either.  But the brothers spend so much time killing monsters, and the occasional evil human, that animals must seem innocent by comparison, and killing them is not something that they would relish.
Even when they summoned crossroads demons, a ritual that requires a black cat bone, they recycled the one they found in “Crossroads Blues”.  Contrast that with the woman who wanted to find out the truth about her boyfriend’s cheating and killed her cat to summon Veritas in “You Can’t Handle the Truth”, or Scott Carey, the special child from “Hunted” who killed his neighbor’s cat at Azazel’s urging to test his powers.
On one occasion it was hinted that one of the brothers might have harmed an animal for a supernatural purpose: dog blood was needed to kill Veritas.  A soulless Sam provided the supply, and when Dean asked about it, Sam said that he probably wouldn’t want to know about the source.
Supernatural Animals
The primary supernatural animal featured on Supernatural is the hellhound.  These beasts hunt down those who have made deals with demons when their time is up.  The damned person they are chasing can see them, and so can demons, but to the average person they are invisible.  Drawings of hellhounds suggest that they are hideous.  They can be injured, drawing visible blood, and killed.  They are vulnerable to salt and iron, as well as Ruby’s knife and an angelic sword.  Origins have not been discussed for the hounds.
Other creatures are mentioned in passing.  Nessie.  Black dogs.  More likely exist, but seem to cross paths with the Winchesters less often.  Because hellhounds accompany demons, they are encountered more frequently.
At first glance, the newest supernatural entity, the “Khan worm” created by Eve, might be classed as an animal.  It is non-human, to be sure, but can possess humans, and has the intellect to speak like one, and hide the possession.  For these reasons it is perhaps best to classify it as a monster.
Characters and Their Interactions with Animals
The animal interactions discussed so far have not been overly positive.  Even family pets are not always safe.  Several of the families Sam and Dean encountered in their travels have had dogs, some of which react to danger like the dog in “Skins”, while others end up being dinner, like Buster in “Family Remains”.  And then there was poor Freckles, who was “mean” to Lilith-in-the-little-girl…
It would be depressing to think that animals had no other role in Supernatural than to be victims or pests.  Thankfully, there have been some happy – or at least comical – moments, even if they later turned sad.
Poor Dean, infected by ghost sickness, had a close encounter with a bow-wearing Yorkie in “Yellow Fever” and ran in terror.  In the same episode, a cat jumped out of a locker and made him scream like a little girl.  Later in “Exile on Mainstreet”, Dean, under the influence of a djinn, got spooked by another Yorkie hiding in a shed.  As it happens, Dean once claimed to have a Yorkie during “Devil’s Trap” as a fake excuse to get into a building.  He seems to like animals, given his regard for the rabbit mentioned above, and his attempt to pet the golden retriever tied up in “Mystery Spot”.  Of course, after he smiles, says “hey buddy” and goes over to the dog, it mauls him to death.
Other characters have had pets.  Sam managed to have a dog for two weeks growing up.  He once ran away from Dean and John and hid out in Flagstaff, Arizona, with a golden retriever named Bones.  Bones appeared in Sam’s heaven.  In the alternate universe, Jared Padalecki and his wife had a pet alpaca.  Bobby had a Rottweiler named Rumsfeld at the salvage yard that slept on the hood of a truck.  Meg killed him at the end of the first season.  Bela had a Siamese cat for a companion in her apartment.  
Even non-human characters have had their faithful friends.  Gabriel, in his first appearance masquerading as the Trickster, had a Jack Russell terrier.  One could argue that this was just one of his many illusions, but he treated it like a real animal, talking to it, petting it, and offering it food.  He thought of it as a pet.  Then there is Crowley and his hellhound.  A bigger beast than average, it obeyed his commands, even if it meant attacking another hellhound.  He seemed proud of it, and called it “my pup”.  Veritas had her legion of cats, eagerly feasting on the bodies of her victims.
Historically, both cats and dogs have been accused of being familiars, spirits associated with witchcraft.[10]  Cats were sometimes burned preemptively in the middle ages.  In retellings of Faust, Mephistopheles appears at times as a black dog.
The only real conclusion is that animals should run as fast as possible from any supernatural entity.  As much as the characters on supernatural may like animals, they are not necessarily able to protect them, and sometimes need them for their own purposes.  In real life, at least, there are charities that do their best for animals, like local humane societies and Jared’s favorite A Dog’s Life.
So to all the furry, feathery, and crawly creatures, be careful who chooses you as a friend.