You'll be glad to have these crawlers in your garden, because they are a sign for rich soil.

What is one of the easiest ways to tell if your garden's soil is healthy? Turn over a spade full of earth and count three or four earthworms squiggling away -- it's a sign of rich, productive soil.

The more earthworms, the better, because those amazing wigglers contribute to soil fertility, drainage, and texture. If earthworms don't call your garden home, then it's time to take action and make the place more welcoming to them.

Earthworms improve the soil and boost plant performance by transforming organic matter, such as compost, decaying leaves, and rotting manure, into humus and worm castings. Otherwise known as black gold, nutrient-rich castings and humus represent the holy grail of gardeners seeking great soil.

Don't add earthworms to your garden in hopes of improving the soil, though. Add organic matter to attract earthworms. Work chopped leaves and compost into the soil in spring and fall, then welcome the earthworms.