Photo courtesy USDA
The earthworm is a lowly animal, we might think.
To some people its primary function is fishing bait. But the more we study earthworms the more we find how diverse and complex they are. And they may be doing a lot more for us than we know.
On Planet Earthworm there was a whole lot going on this week that illustrated this point.
The UK’s garden earthworms are far more diverse than previously thought, a discovery with important consequences for agriculture, Cardiff University scientists said today.
“Many of the common earthworm species found in gardens and on agricultural land are actually made up of a number of distinct species that may have different roles in food chains and soil structure and ecology,” said Bill Symondson, lead researcher. The research is published in Molecular Ecology.
They made the discovery while trying to identify earthworm DNA in the guts of slug and worm-eating beetles. Watch this video explaining the research:
“We started getting results that were not really what we expected to see and that indicated the presence of several new earthworm species,” Symondson said. “After investigating this further we eventually found that there are significant numbers of what we call ‘cryptic species’. These different species live in the same environment and have the same outward appearance, but do not interbreed and have clearly distinct DNA sequences.”
Why is this significant?
Earthworms play a major role in the agricultural environment because they are involved in many soil processes such as soil turnover, aeration and drainage, and the breakdown and incorporation of organic matter, Symondson explained. “For this reason, they have often been the subject of research into ecology and toxicology. It is vitally important that we know exactly which species we are studying, in case they respond differently from one another — to agrochemicals or heavy metals in the soil, for example.”
Further earthworm research will now have to be done with the knowledge that in many cases there are multiple species where it was thought there was just one, Symondson said. “We need to establish for certain whether the different cryptic species play different roles in the ecology of our agricultural land or have different tolerances to potential environmental stresses such as toxins, parasites, or extremes of temperature.”
Earlier this week, National Geographic News reported that newly evolved “superworms” that feast on toxic waste could help cleanse polluted industrial land.
“These hardcore heavy metal fans, unearthed at disused mining sites in England and Wales, devour lead, zinc, arsenic, and copper,” wrote our UK-based contributor James Owen.
The earthworms excrete a slightly different version of the metals, making them easier for plants to suck up. Harvesting the plants would leave cleaner soil behind, Owen reported.
“These worms seem to be able to tolerate incredibly high concentrations of heavy metals, and the metals seem to be driving their evolution,” said lead researcher Mark Hodson of the University of Reading in England.
Two other superworms, including an arsenic-munching population from southwest England, are also likely new to science, Hodson said.
Experiments suggest the superworms make the metals easier for plants to extract from the soil.
“The earthworms don’t necessarily render the metals less toxic, but they do seem to make them available for plant uptake,” Hodson said. This raises this possibility of using the earthworms as part of efforts to clean up land contaminated by mining and heavy industry.
- According to the U.S. Department of Agriculture, there are 23 families and 7,000 species of earthworms. They are hermaphrodites and range in size from fractions of an inch to yards in length. A square yard of U.S. cropland would yield 50 to 80 earthworms of different species, the agency says.
Photograph by Jane Andre
New varieties of the Lumbricus rubellus earthworm can eat hazardous waste, researchers reported in September 2008. Above, the “reference” earthworms are normal, whereas the “stream” and “cottage” earthworms have evolved to survive in soils contaminated with high amounts of lead and zinc. Read the National Geographic News story for details of this research.
More from National Geographic News:
National Geographic Animals: Common Earthworm
U.S. Department of Agriculture: Earthworms