Eelworm, any of the minute nematode worms, the largest being less than 1/50 in (0.5 mm) long. They are found in vast numbers in soil, in fresh water, and on the seashore. Many attack plants and insects and some are serious pests. The stem and bulb eelworm, for instance, stunts or kills a wide variety of crops, such as cereals, bulbs, and strawberries. They may be transmitted by plant-sucking bugs and themselves transmit diseases such as tobacco mosaic.