Question

Investigative Extensions 1. Earthworms are among the most familiar inhabitants of soil. They play an important role in improving the texture of and adding organic mat- ter to soil. You may have read Darwin's estimate that over 50,000 earth- worms may inhabit one acre of British farmland. Earthworms are readily available from biological supply houses, or you may collect your own to use in experiments. Following are questions that you might investigate. a. Why do earthworms come out of their burrows when it rains? Is it because they may drown in the water in their burrows? Does rain stimulate mating behavior, and the worms are coming to the surface to mate? Does the pH of the soil change as it rains, and is the burrow becoming too acidic or alkaline? What is the optimum pH range for earthworms? Does rain create conditions more favorable for migra- tion to new habitats? b. What effects do chemicals used in agriculture have on earthworm populations? Compare numbers and health of earthworms in con- tainers of soil to which varying amounts of fertilizers, pesticides, on herbicides have been added. c. Do earthworms in the soil stimulate plant growth? Compare the biomass of plants grown in containers with and without earthworms present. 2. An amazing diversity of organisms has evolved from the foot-mantle- visceral mass body plan of molluscs. Living terrestrial, freshwater, and marine snails and bivalves are available from biological supply houses, aquarium supply stores, or from ponds or terrestrial sites in your area. Consider the following questions that you might investigate. (A Google search for "snail experiments" yields over 1,140,000 entries, including experiments being performed in the International Space Station.) a. What effect does sedimentation have on aquatic snail populations? Consider changes in water chemistry and/or substrate. b. What effect does temperature have on the growth and/or reproduc- tion of aquatic or terrestrial snails or slugs? Why would this question be of interest? c. Invasive aquatic plants have become a major concern of scientists worldwide. For example, water hyacinth, introduced into ponds in

Answer 1

1a. When it rains, the soil surface gets wet. The earthworms can move across this soil easily as they find it easy to move in wet surfaces. So, they come out of their burrows and move across this wet soil. If it rains heavily, the burrows are filled with water and oxygen becomes low and it becomes difficult for the earthworms to respire. They come outside to respire. Wet surface also helps worms in finding mate. This is another reason for coming out.

The pH of normal rain is 5.0 to 5.5. So, it makes the soil acidic. pH of soil also depends on its mineral content, but definitely decreases due to rain as rain is acidic. Burrows become acidic, but that is within tolerable range of  earthworm. They can tolerate a pH from 5.0 to 8.0.

As wet surface helps earthworm in movement, it is easier to find new habitat and migration to new habitat. It not only helps to find new habitat but also food and mate (mentioned earlier).

b. Chemical fertlizers, pesticides and herbicides usually lower the pH of soil and sometimes destroy the earthworms. They do not always kill the earthworms. If containers containing different concentrations of chemical fertilizers are compared, the number will decrease and health of earthworms will be detoriated which contain high concentration of chemical fertilizers, pesticide or hebicide.

c. Earthworms help the plants in fixing nitrogen from soil, which is essential for plant growth and thus earthworms help in stimulating plant growth. Biomass of the plants will increase, which contains earthworm.