The soils supporting our home lawns, vegetable and perennial gardens are improved by the presence and activity of earthworms. They are considered beneficial in the plant world. Earthworms move through the layers of soil creating tunnels for water and oxygen to reach the plant roots and channels for root growth. Their movement increases drainage and reduces compaction. Often called “nature’s rototillers”, earthworms feed on organic matter, bacteria, fungi and small soil particles in varying depths depositing their castings, or feces, in other horizons effectively turning the soil over. Castings are rich in nitrogen and nutrients easily absorbed by plants. Their feeding aids decomposition of organic matter, aerates soil, creates good soil structure and develops humus. The Rothamsted Experimental Station in England has done research finding as many as 250,000 earthworms per acre. That is a lot of subterranean work happening! Charles Darwin was one of the first scientists to recognize the benefits of earthworms. His last book written in 1882 is on the worm biology and behavior. His discoveries of earthworms are still being seen today.
Often after a rain, earthworms come to the soil surface then re-enter the ground head first. Some scientist think the worms come to surface for air if the ground is saturated. Others believe chemicals in the rain are inhospitable by changing pH and chemical amounts from acid rain. Still others think since the surface is moist, the worms come to the surface to mate. Earthworms are negatively affected by drying out by the sun therefore most surfacing happens at night. The action of tunneling back into the ground squeezes the worm leaving a pile of castings above ground. The casting look like tiny round balls piled up in a pyramid up to two inches depending on the size and type of the worm. Casting piles normally go unnoticed unless the turf is cut exceptionally short like that on golf course greens and tees. Home lawns should be cut to a height of at least three inches. Wet piles can stick to mowing equipment gumming up the blades and gears. The piles are easily dispersed once they dry.
Earthworms breathe through their skin. Oxygen is absorbed by mucous on the outside surface of the worm where it is transferred to the internal organs. This is called a gas exchange. The circulatory system of the earthworm contains five hearts or aortic arches. They pump fluids to blood vessels and capillary beds throughout the body circulating back to the hearts. The earthworm’s digestive system starts with its wide opening of a mouth that its throat or pharynx protrudes out of grabbing organic matter, soil particles and all that they contain. This food is swallowed down to a storage area called a crop. The food then moves to the gizzard where it is ground up by strong muscles and tiny stones and grit swallowed by the worm. Once the food is sufficiently ground, it moves to the intestines where digestive juices extract nutrients and some are absorbed by the worm. Excess digested food is then excreted as worm castings. It is these castings that are rich in nutrients readily available for plant roots to pick up. Earthworms don’t have eyes but are sensitive to light, vibration, touch and chemicals. They want to be in darkness and will move away from the light.
Chemicals added to lawn and garden can kill the earthworms. Preferred pH levels are neutral to 6.6. Adding lime in large doses can be too shocking of a change in their environment. Many earthworms will move to areas with better suited conditions or they may just die. Some insecticides and fungicides have lethal effects on earthworms. Researchers have also found earthworms within chemically treated soils to contain up to 20 times the toxin levels than the soil the worms inhabited. Stored toxins built up in the earthworms could then be passed up the food chain to animals using the earthworms as food.
Earthworms are classified as animal invertebrates. They are in the phylum group Annelida, meaning segmented worms. Each segment contains four tiny setae or claw like bristles used to move through the soil. Worms are hermaphroditic; each worm has both male and female parts with the male pores located on the outside of the animal. Earthworms are not self fertile. They need another worm to mate and reproduce. Each worm is fertilized in the mating process called cross-fertilization.
The most common earthworms found in Connecticut are Lumbricus terrestris, called the Night Crawler, and Lumbricus rubellus called Red Worm. Night crawlers are known to venture deep into the soil in permanent vertical burrows. The will come to the surface to feed also. Red worms prefer to live in a manure pile or area with high organic matter. Both of these earthworms originated in Europe and were introduced to North America unknowingly on plant material, ship ballast, wheels and shoes of immigrants. Native earthworm finding are very rare. It is not known whether native types were wiped out by glaciers scraping the earth or if the new earthworm invaders displaced the old. Different theories exist. What is known is that the earthworms that are present today are many, active and busy decomposing and recycling organic matter in rich new topsoil.
There are some invasive worms originating from Asia that are causing problem in some areas of North America. They are such fast consumers of organic material they are changing the layers of soil and eliminating the forest floor called ‘duff’. Some birds nest in the duff areas to raise their young. Insects and animals that also reside and feed in the fast disappearing habitat are also finding it hard to live. The effect of the exotic worms in the local habitat really is upsetting the ecological balance. Some populations that depend on the areas the worms are ruining might vanish forever. Research is presently being done but much more needs to happen. So does education of the general public. Some fishermen are using invasive worms for bait, then just dumping the leftovers on the ground. They are unknowingly spread the invaders. ATV and off-road enthusiasts also can pick up soil, worms and eggs in tire treads, then depositing them far from the initial infected site. Hopefully in the not too far future, more information and education programs will be available. Keep watching!