Maple syrup and honey are both hygroscopic in nature. That is, they absorb the moisture from organizms and soft tissues, such as meat. This is because of the extremly high sugar content. Nothing grows in honey, though some spores can exist in the sticky stuff, but not grow until more liquid is added. Syrup has more liquid in its sugar/liquid ratio. There are very few molds or other organisms that can live in it, and fortunately for us, are harmless to us, though they taste nasty. Though there is water in maple syrup, it is unavailable to most organisms. Instead, the sugar sucks the moisture out of them and they die.
As was previously stated by others, simply skim the mold from the top of the syrup, and then, if still feel funny about it, Carefully wipe the jar where any mold might have grown, and transfer the syrup to a clean, sterilized container.
In the Eastern U.S., and the Great Lakes region, people have been doing this with syrup for centuries, and I've never known anyone to get sick from eating maple syrup.
As with all things, use your best judgment. If you are uncomfortable using maple syrup, or any other food, throw it out. Myself, I've got the proverbial cast iron stomach. I'd skim it and use it.
Seeeeeeeya; Goodweed of the North
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