Moles are of minor importance except where they are abundant, when they can be a real nuisance. You may be surprised to learn that moles do not eat roots, tulip bulbs, and so on, although often blamed for disappearance of these plant parts. Moles do approach or touch underground parts of plants as they burrow through soil looking for insects on which they feed. In doing so, they often open a passageway for mice or ground squirrels which do eat bulbs.
Because they feed solely on insects and other soil animal life, moles can best be driven out of a lawn or garden by treating the soil with insecticides such as chlordane, dieldrin, calcium arsenate, ar-senate of lead, or DDT. With their natural foods eliminated, moles will quit burrowing through the treated soil.
The tiny (sometimes microscopic) thread-like creatures called eelworms or nematodes (nemas to the scientist) are the most mysterious and least understood of all creatures inhabiting the soil. Zoologists regard them as a race apart from other worm-like soil dwellers. They were known to early microscope workers, but considered of no economic importance and generally ignored until about 30 years ago.
Some animal-parasitic nematodes are beneficial, but practically all plant-parasitic species (both leaf and root nematodes) are injurious. And contrary to common opinion, most nematodes are not killed by freezing. There are nearly 10,000 known species of nematodes, several hundred of which are known to attack plants. (Much work is yet to be done in classification.) Because of the ease with which these creatures mutate and produce new forms, the nematode threat is enlarging.
The first recognized soil-pest menace to plant life in America (or at least the first considered important by Federal authorities) was the importation of nematode-infested narcissus bulbs from Europe in 1926. In that same year a disease called spreading decline was classified as a serious threat to citrus grooves in Florida, but was not associated with nematodes at the time.
All during the 1930's the science of nematology was relatively neglected. Then in 1941 the discovery of a full-scale infestation of a species called golden nematode on Long Island set off a furious "crash program" to bring our knowledge of nematology into line with the threat presented by these creatures. The golden nematode, known to be a dangerous pest of potatoes, is one of the cyst-forming species, which possesses a peculiar type of female immortality. Older females do not die but form an egg-like cyst which can remain dormant for years. This cyst then regenerates when conditions are favorable. Once in a soil, cysts can survive for decades, without any outside source of food or water. Years after the soil has been fumigated and treated with nematocides, cysts may still regenerate, so a constant watch and recheck of the area must go on.