Nature’s Hitchhiker
By: Jessica Hoffman
Earthworms: nature’s soil managers. Aerating the land like an adept farmer, earthworms increase soil moisture and break up compact dirt. However, those slimy, long worms that are dug up in back yards across America are likely nonnative and invasive! While you may think they are wholly beneficial, the nonnative species can actually be harmful. The extent to which the nonnative worms travel was completely underestimated. A new study finds that these invasive worms can travel quickly and can spread populations far and wide.
How did the invasive worms get in your backyard? Although it seems unlikely, the earthworms you find probably arrived because of you! Earthworms are masters of hitchhiking, traveling in the bait cans and shoes of unsuspecting people for miles and miles. An old brown boot can quickly become a cocoon RV, housing and transporting the future worms. Sneaky and unforeseen, the worms are shown to populate in higher concentrations along roads and waterways. These slow moving travelers take advantage of speedy cars, boats, and other forms of transportation to spread their families all over the world! The study measured the hitchhiking capabilities of the worms by surveying several plots of land for the different species of earthworms and its density twice, with a six-year gap in between. Originally estimated at 5m/yr, the new study estimates the nonnative earthworm population spread rate to be 17.9m/yr!
The earthworms form clusters like neighborhoods, called jumps, and then their peculiar form of reproduction really takes off! The worms begin their own urban sprawl. The recent study found that with frequent jump dispersal, there were larger earthworm populations. The worms were able to jump, or travel to a new area and populate a dense cluster. This finding is logical. Jumps have a positive feedback loop in which increasing clusters leads to more and more clusters. When factoring in jump dispersal, earthworm population spread rate increases to 27.9m/yr! The study collected density data only twice so jumps were estimated with some uncertainty and moderate margin of error (3.79m/yr).
These results may seem insignificant, but bear in mind that invasive species disrupt ecosystems. In the case of the hardwood forests in Minnesota, the invasive worms eat the leaf litter, which destroys the soil quality of the area. Trees and wildflowers die from the lack of nutrients. These little creatures can disturb organisms higher up on the food chain too, killing off the vegetation leaves other animals hungry. Rest assured, you are not totally to blame; the spread in population of invasive earthworms is also dependent of abiotic factors like soil texture, pH, organic matter, soil moisture, vegetation etc. Invasive species will not establish a population if the nonliving conditions are not suitable for their taste. We may put the worms in their place but if they can’t survive well then…
Works Cited
Cameron, Erin, and Erin M. Bayne. “Spatial Patterns and Spread of Exotic Earthworms at Local Scales.” Canadian Journal of Zoology (2014)
doi. 10.1139/cjz-2014-0197