What is the difference between a mermaid and a siren?
The tl;dr version: Technically, a siren is a half-bird, half-woman hybrid from Greek mythology; a mermaid is a half-fish, half-woman hybrid from Northern European folklore. Over time, “siren” has become interchangeable and synonymous with “mermaid.” Generally, both refer to the half-fish, half-woman hybrid of Northern European origin.
However, for all of you who enjoy the history behind this change, keep reading!
How the bird-woman siren became a fish-tailed mermaid is a bit unclear – but that doesn’t stop historians from having theories! One of the more intriguing facts is that “wing and fin, in Greek, are both designated by the same word.” In Latin, the words for wing and fin have only one vowel difference. I like that very much, as it gives credence for it being both, and: both fish-tailed, and bird-winged. It was simply a difference on how you translated it.
Meri Lao suggests that the “fish-formed and winged Sirens shared the same cradle” in the Mediterranean. This is based off of two archaeological finds showing Odysseos with fish-tailed sirens. One is a vase from Megara dating from the 2nd century BC. The second is a lamp found in Britain, dating from the 1st-2nd centuries. (She does not specify BC or AD, but seeing as how it was found in Britain, I think it most likely to be AD…but don’t quote me on that.)
As much as I love the idea of “both, and” in this case, I think it’s too good to be true. The Roman lamp can be ruled out as evidence; it was common for the Romans to assimilate the culture of the conquered people into their own. It is not proof in and of itself that fish-women came from the Mediterranean. It’s more likely that the Romans saw a mythical design they liked and mimicked it.
The vase is more interesting, and yet it also has a northern explanation: the Celts (from northern Europe) conquered Galatia in Asia Minor (think Turkey) in the 3rd century BC. This would place the vase – which is a unique find – perfectly within context of having a Celtic influence within a Grecian world. I submit that the Celts brought the folklore of the mermaid to the Mediterranean, and it became entangled with the Greek Sirens. (And perhaps they confused the word meaning wing and fin, too.)
When and Why did Sirens become fish-tailed?
Regardless of which came from where, the two iterations co-existed until “the folklore Renaissance of the 1800s.” That’s right, the Victorian Era ruined the mermaids, like so many other things in life.
Just kidding….kinda. I have lots of beef with the Victorians, but the relevant issue here is women were taught that intimacy was shameful. Thus, the mermaid encapsulated the Victorian woman – she was desirable, and yet unattainable. After all, the tail was “the ultimate chastity belt.”
The arts played a huge role in this, too. Mermaids were a popular topic of paintings, which depicted mermaids as half-woman, half-fish. They’re the reason we think mermaids look a certain way. And so, we are cemented in thinking that mermaids are exclusively half-fish, half-women creatures.
Next, many folklore stories were collected and edited in the Victorian era. The stories call them mermaids, even if they clearly look more like women (see Kidnapped Mermaids). Countries less effected by the Victorian era (i.e. Germany, Scandinavia, and eastward) hold truer to their traditional maidens of the deep. Thus, it’s quite possible that the “mermaids” originally had legs and resembled what we now would call a water spirit rather than a mermaid.
Be that as it may, our culture has bequeathed the fish-tailed mermaid the attributes of the bird-winged sirens (like trying to kill sailors). We are often none the wiser that there is a difference, and find any other mermaid type strange.
Sirens and Mermaids aren’t the only “mermaid types.” There are selkies, nix, undines…the list goes on! Check them out here!
 Meri Lao, Sirens: Symbols of Seduction (Rochester, VT: Park Street Press, 1998), 82.
 Ibid., 88.
 Ian Barnes, The Historical Atlas of the Celtic World (Edison, NJ: Chartwell Books, Inc., 2009), 27.
 Heidi Anne Heiner, Mermaid and Other Water Spirit Tales from Around the World (Nashville, TN: SurLaLune Press, 2011), 1.
 Skye Alexander, Mermaids: The Myths, Legends, and Lore (New York: Adams Media, 2012), 34.
 Ibid., 33.