Giant ragweed (Ambrosia trifida) is one of the main contributors to the hay fever that causes distress to millions of gardeners this time of year. While giant ragweed is quite capable of spreading through gardens and fields on its own, it's also getting help from one of a gardener's best friends: the earthworm.
Weed ecologists at Ohio State University have found that earthworms are moving seeds of giant ragweed around in the soil, effectively spreading this weed wherever they go. More than two-thirds of all giant ragweed seedlings studied emerged from earthworm burrows. Researchers began investigating this phenomenon because giant ragweed produces few seeds, yet it's readily spreading in gardens and agricultural fields.
While earthworms also collect seed from other plants, such as sunflowers, giant ragweed is a preferred plant. Earthworms forage for seeds and bring them into their burrows, often located only a few inches below the soil surface -- a perfect place for weed seeds to germinate.
For more information on earthworms as weed farmers, go to: Weed Science Society of America.