Earthworms are a welcomed sight in many gardens and yards since they can improve soil structure and mixing. But they are hard to find in the drier soils of eastern Colorado where water and organic matter is limited. Adding earthworms to fields where they are not currently found could help enhance the health and productivity of the soil. In areas where droughts are common, though, can earthworms survive? A new study suggests that they can. Earthworms use water for many things -- for respiration（呼吸）, to keep their bodies from drying out, and to make the mucus（粘液） that helps them slide through the soil. When soils get dry, earthworms go into estivation（夏眠）.

"During estivation, earthworms wrap their bodies into a tight knot to reduce the amount of surface area exposed to the soil," explains Jacob McDaniel, lead author of the study published in the September-October issue of Soil Science Society of America Journal. "Then they'll seal themselves up in a chamber lined with their mucus. Inside that chamber, the humidity is higher so they don't dry out as the soil dries."

The ability of earthworms to go into estivation suggests they can survive dry periods in the soil. The aim of the current study was to find out how long they could survive and whether they would recover after an extended drought. To answer those questions, researchers from Colorado State University recreated drought conditions in pots containing soil and worms.

Earthworms live in Colorado soils, but their distribution is limited. They are mostly found in areas close to water or with higher levels of precipitation or irrigation. Earthworms for the current study were gathered near an irrigated alfalfa field close to Fort Collins. If these worms can survive periods of drought, they could be established in no-till, dryland agricultural soils of eastern Colorado to improve and mix soils.

Four different levels of drought stress were created for the study: constant water and one, two, or three weeks without added water. These conditions were based on rainfall patterns in the area where the soil for the study -- a sandy loam from a dryland agricultural field -- was collected.