Theory: āVampireā Bats
āSoon actual darkness was coming into a stormy sky; while still the great bats swirled about the heads and ears of elves and men, or fastened vampire-like on the stricken.ā- The Hobbit, chapter 17: The Clouds Burst.
I am far from the first to suspect that these bats are not actual vampire bats as we know them.
All known species of vampire bat are native to the New World tropics. Furthermore, while vampire bats have been documented feeding on human blood; they only do so when their usual prey (ungulates and birds) are scarce, and they certainly donāt go out of their way to bite people.
However, I do think that there is, or more accurately, was a real bat species that fits the description of the bats from āThe Hobbitā.
Necromantis - Wikipedia
Necromantis lived in Europe and North Africa during the Eocene. While Eocene Europe was much warmer and wetter than modern Europe, Necromantis still wouldnāt be as geographically misplaced as an actual vampire bat would be.
This large bat was almost certainly a carnivore; with strong jaws and sharp teeth. Many scientists theorize that Necromantis was an active hunter of smaller vertebrates, similar to the modern spectral bat. However, an older theory-from which Necromantis derives its name, meaning āDeath Eaterā-holds that this bat was a scavenger. The behavior demonstrated by the bats in āThe Hobbitā-following larger predators, and preying on the dead or dying-is perfectly in line with that of many scavengers.
These bats being at least similar to Necromantis would also explain why the orcs tolerate their presence to begin with. Its unlikely that they would appreciate being followed by bloodsucking parasites; but a small hunter and scavenger would provide useful pest control and garbage disposal services, similar to the ancestors of domestic dogs and cats.
For the Goblins of the Misty Mountains, the benefits of living with the bats wouldnāt stop at cleanliness. With their keen hearing, bats could provide an intruder alarm for orcs living deeper in the cave. The bats might be trained to carry messages, similar to the birds employed by other races. Even bat feces can be a valuable resource: nitrogen-rich guano can be used as fertilizer, food for edible insects, and even as a source of raw ingredients for gunpowder!
The bats, in turn, would gain protection from predators and rivals; in addition to a reliable source of food. Orcs might even provide veterinary care to sick or injured bats; and build bat houses when natural roosts arenāt available.
Thus, two demonized species work together for mutual survival in a harsh, rapidly changing world.
