On a wet day, you will usually see a lot of earthworms on sidewalks and roads. But what makes the worms crawl away from the protection of the soil when it is raining?
Some individuals assume worms come to the floor so they don’t drown of their burrows. However, “worms do not have lungs like we do,” Thea Whitman, a soil scientist on the University of Wisconsin-Madison, instructed Live Science.
Instead, earthworms soak up oxygen by their pores and skin, and so they can achieve this from water in addition to from air. “I’ve saved earthworms in water for days, and they don’t die,” Kevin Butt, an earthworm ecologist on the University of Central Lancashire in Preston, England, instructed Live Science.
In truth, a 1956 examine discovered that 5 earthworm species “have been all capable of dwell for 31 to 50 weeks in soils that have been completely saturated with water,” Whitman stated. “So lengthy as there may be oxygen within the water, these worms will nonetheless be capable of breathe.”
Still, Whitman famous {that a} 2008 examine of two earthworm species found that oxygen consumption would possibly play a job in why some, however not all, earthworms are likely to floor on wet days.
“The species that required larger oxygen ranges was extra prone to crawl out of its burrow throughout wet situations,” Whitman stated. “The species that did not require such excessive oxygen ranges was much less prone to come to the floor. Thus, some species of worms are extra vulnerable to low oxygen ranges, and could also be extra prone to depart their burrows resulting from a heavy rain, whereas others could stay fortunately belowground.”
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Another in style principle is that the “vibrations from the rain are perceived by the worms to be just like the vibrations that usually warn them a mole is coming,” Whitman stated. “The thought is that the worms could come to the floor throughout rain to flee what they assume is a predator.”
However, Butt discovered this concept extremely unlikely. The actions of a predator resembling a mole within the soil wouldn’t be rhythmic, so they might “be distinguishable by the earthworm from that of rain,” he stated.
Another risk is that “rainwater within the soil harms the worms in a roundabout way — for instance, if the rain have been acidic, or if dangerous chemical compounds, resembling heavy metals, have been launched,” Whitman stated.
Although the 2008 examine didn’t discover proof that dangerous compounds in rainwater drove worms out of the soil, Whitman did be aware that worm researchers typically use chemical compounds to collect worms. “Pouring a mix of mustard powder and water onto the soil irritates the worms and drives them to the floor, the place they are often collected and analyzed,” she defined.
Butt urged the most certainly rationalization is that earthworms floor on wet days to maneuver extra rapidly on the moist floor, as an alternative of slowly burrowing by soil as they often do. “They require moist environments to outlive, and so moist days may permit for them to journey above the soil,” Whitman stated. Earthworms would possibly make such journeys to mate or migrate, she added.
This rationalization may assist make clear a observe referred to as “foot trembling,” which is seen in some birds and reptiles, Butt stated. Instead of producing sounds by transferring inside the soil as moles do, these animals apparently stomp on the floor, producing vibrations which will mimic these from rain. These vibrations “may cause earthworms to come back to the floor and fall prey to the predator,” Butt stated.
A custom often known as “worm grunting,” “worm fiddling” or “worm charming” takes benefit of this earthworm response to vibrations. Using a stick or a noticed, individuals generate vibrations within the soil to entice worms to the floor, the place they’re harvested for bait. In addition, worm charming “is now used competitively in some cases,” Butt stated, such because the annual “Worm Gruntin’ Festival” in Sopchoppy, Florida.
