One minute, your yard looks fine; the next thing you know, holes are popping up.

These are a bit perplexing, though, because there aren't any mounds of dirt that indicate digging from a gopher, groundhog, or mole. So where did they come from, and what's causing them?

In most cases, you'll never see what's causing these mysterious holes since they happen at night or, in some cases, out of sight.

According to the MSN website, holes without mounds could be a variety of animals or insects.

SKUNKS

You'll be able to see the bottom of these holes, and they literally pop up overnight. They're a few inches wide and deep from skunks digging for food only but not to live.

RATS

These holes are three to four inches long and have several entrances for rats to access their nests. They are very smooth and hard-packed.

BABY RABBITS

Momma rabbits build shallow nests in the ground to hide their babies. These holes will be surrounded by dead grass, often covered with leaves and other vegetation, to hide the babies for safety reasons. These holes will be near fences, trees, or other areas that aren't out in the open.

CHIPMUNKS

These furry rodents create an entire underground burrow system with round holes around two inches wide that are so neatly dug they're difficult to see. The chipmunks actually pack the excavated dirt into their cheeks to avoid mounds of dirt.

VOLES

These teeny creatures create holes the size of golf balls, sometimes oval-shaped, so it may take you a while to notice them until there are several.

YELLOW JACKETS or GROUND-NESTING BEES

These insects build nests in leftover holes dug up by rodents or small animals that are no longer using them. Any size hole will do, and you may even notice the hole slowly grow over while getting bigger as the underground nest gets bigger.

Yellow Jackets tend to use dryer dirt, while bees living underground will start to create tiny holes about a half-inch wide when the rodent hole starts to fill in. It will also look sandy.