By David Wall, Mount Pleasant Master Gardener
I realize rains have been in short supply recently, but have you ever gone walking across your yard after a rain and noticed the number earthworms (from now on, just worms) on the ground surface? How about in the morning when the dew is heavy? How about going out on a hot day and finding dead worms on your sidewalk, curb, and driveway.
The obvious answer is they come to the surface because they’re drowning, but that’s not the case. Worms breathe through their skin (not lungs), and need moisture to do that. Also, most worm species can survive submerged for up to two weeks.
There are several theories on this. One says that worm species most active at night need more oxygen, are more likely to come to the surface in a heavy rain. This is possible for some species, but certainly not for all, as other species won’t come to the surface period.
Another theory is that raindrops sound like vibrations put out by moles, so they come to the surface to escape. Some fishermen produce these vibrations with sticks or electrical current, catching surfaced worms for bait. Funny thing about this is only adult worms come to the surface, no juveniles.
A more likely explanation is they can move easier and faster on the surface. They can move to new territory, perhaps searching for a mate. The problem is they need moisture, and if the surface heats and dries too fast, they perish. Even though they can tell the difference between night and sense they’re since drying out, day, you’d think they’d race to get back underground. Unfortunately, if they happen to be on the sidewalk, curb, or driveway, drying may occur before they can get to shelter. That’s why we see so many carcasses on concrete.