It’s because they don’t want to drown, right? Nope! This is a common misconception. Scientists have done research and discovered that the main reason is because they love the wet ground and pretty much come out to travel and mingle! – A much happier reason.
Earthworms respire through their skin and require moisture in order to breathe. Their skin is covered in mucus secreting cells that help to take in oxygen, which won’t function when it’s dry. Even though rainy days may not be the best days to drive around for humans, they are perfect days for Earthworms! The grey weather gives them an opportunity to move a greater distance in less time. The worms know it’s rainy out because the can feel it! As the rain hits the ground, vibrations are given off. These vibrations are similar to when a predator, like a mole, is around, causing the worms to wiggle as fast as they can to get above ground. Once above the soil, they feel free to travel since the ground is wet enough.
Once the worms are out and about, it is easier to mingle. They often congregate in small groups which make things a little easier to find mates. Worms are hermaphrodites, meaning that both worms have male and female parts. This method of reproduction is extremely helpful when most of a worms life is spent underground in an area that is not conducive to mating. Both worm partners are able to fertilize eggs and have baby worms! Sponges, snails, and sea anemones reproduce in a similar manner.
Without the rain to signal that it’s time to come to the surface, worms would be out of luck in the mating department, and this would not be good. Worms are an important part of the ecosystem. They create burrows in the ground that allow nutrients like oxygen and water to enter the soil, while giving carbon dioxide a place to leave. The worms work with the decomposition process by breaking down dead organic matter and turning it into small pieces that can be used by good bacteria and fungi. The bacteria and fungi then turn those small pieces into nutrients that plants and animals can use. While the worms are burrowing into the soil, they are mixing the layers up, allowing for a greater spread of nutrients. Where there are earthworms, there are good bacteria and fungi helping the plants grow.
Not only are worms, provided they are native species, good for the environment as they help aerate the soil and aid in the decomposition process, but they also provide food directly for animals like birds, turtles, snakes, moles and skunks.
Non-native or invasive worm species can be detrimental. The forests have evolved and adapted to taking up nutrients slowly, so if extra, non-native worms are introduced, they will expedite the nutrient uptake, causing a lot of it to go to waste or to not be used efficiently. One of the biggest ways that invasive worms enter an area is due to fishermen dumping extra bait (worms) out on the ground where the worms can then crawl into the soil. If you are fishing and have extra bait, it is best to dump them out in the water as fish food or keep them for the next trip!
So next time it’s a gray and rainy day, know that while the weather means you’ll be stuck inside, the worms are coming out to have a great time!
Want to learn more about native species or why invasive worms are bad? Read these!