We got an interesting question from a man asking about earthworm populations in relation to the migration of Woodcock, a species of bird that commonly feeds on earthworms. “How do I tell whether a site will produce an over abundance of worms? Woodcock migrate south in October, November, and December”, he continues in his submission. “They eat their weight in earthworms daily. They overwinter in places in the south where earthworms are plentiful. For example, oak and beech leaves have too much tannin to attract worms. Blackberries and switch cane require water to thrive and may indicate better conditions for worms. Is it simply a matter of taking a trowel to remove the leaf litter and counting worms?”

For context, tannin is a polyphenol (a micronutrient) that is present in plants, and an excess of it supposedly discourages earthworms from feeding on any leaf litter from such plants. Now, to answer our reader’s question, it is difficult to tell if a site will attract too many earthworms, and how to tell if you have too many in the first place. If we are understanding the situation correctly, then it seems like he has tried to control their populations to a certain extent, making sure to keep plants that have an excess amount of tannin in them, and that the absence of Woodcock during the winter is what concerns him, as it may bring an over abundance of earthworms.

Usually, one can tell if one’s garden is ripe with earthworms without having to sift through the soil. Earthworms tend to leave behind little mounds of dirt on the top layer of the earth when they surface, which they typically do during more humid conditions (like when it rains). If there are an incredible amount of them, then perhaps that indicates that there is an excess of earthworms. However, we cannot say an exact number that would be considered excessive: it all depends on how big the property is and how nutrient-rich the soil would be without earthworms.

That said, generally speaking, the more organic material there is in the garden (leaves, fruits, vegetables, etc), the more earthworms that garden will attract when those organic materials eventually decompose. So, if our reader thinks his garden might have too much food for earthworms, then perhaps removing some organic debris would be a good idea. Besides, clearing one’s property of leaf litter, as well as piles of twigs and rocks (under which earthworms and other critters may hide), can help maintain populations of multiple organisms, including millipedes.

In conclusion, although we could not provide a concrete answer to our reader’s question, we hope that something we touched on will prove useful. We wish our reader the best of luck with his garden and maintaining the earthworm populations in it!

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