Translation:There is a lizard on the floor in the bathroom.
Fear not, my friend. The lizards in Norden are rarely longer than the length of one's palm. If there is en huggorm på golvet, however... Now that is a reason for concern.
An adder. They are usually shy, though, and since the harsh winters force us to build our houses with good foundations, they rarely find their way indoors - apart from the saunas that we erect on the beaches of our lakes and on the shores of our sea. Generally speaking, the adder is the most dangerous creature you can encounter here; bears, lynx, wolverines and wolves are almost non-existant in Sweden and not much more common in Finland. I am 33 years old and I have seen a lynx once, and although my parents live next door to a bear, they have never seen it. So if you want to pay us a visit, you need not worry. You would be in bigger danger visiting the Rockies.
Does the use of "ligger" here (as opposed to "är") imply that the lizard is dead? Or does it simply imply that the lizard is low to the ground?
The lizard is so low to the ground as you say that we'd probably see it as 'lying' most of the time, so it doesn't have to be dead.
For some reason my exercise said "det sitter en odla..." so i said "there is a lizard sitting on the floor in the bathroom," and of course it counted that wrong.
You didn't happen to grab a screenshot of that? It sounds like there must be a bug here and it's one I haven't seen before. The incubator tells me that this sentence hasn't been changed for 2 years, and sitter is not in any accepted answer. So I'm a bit concerned about whether Duo has come up with some new "clever" algorithm that bypasses our choice of accepted answers.
when does one use "det ligger en..." and "det är en"? In an earlier sentence, it is Det är en orm i skon. Would it be wrong to say Det ligger en orm i skon？
är is a general term and ligger is a spatial one. You can typically use är whenever, and ligger only if it's actually lying down. So your worm example works well. :)
This could certainly be translated as "A lizard is on the floor in the bathroom."