Fly baits used to attract and kill house flies will:

Fly baits are formulated specifically to target adult flies, making them effective against exposed flies. When applied in areas where house flies are commonly found, these baits work by attracting the adult flies, which then consume the bait and are subsequently killed. This method relies on the behavior of house flies, which are drawn to the ingredients in the bait.

The other options do not accurately represent how fly baits function. For instance, while larvae are a stage in a fly's life cycle, fly baits are not designed to kill larvae, as they specifically target adults. Similarly, fly baits do not kill flies in nests since they rely on exposure; flies in hidden breeding areas wouldn’t be affected. Also, while it's possible for baits to attract other insects, this is not the primary purpose of fly baits. Their primary goal is to attract and kill adult house flies that are exposed and feeding, which aligns perfectly with the correct answer.