Eelworms are microscopic soil-borne pests which fortunately are not commonly found associated with houseplants. If, however, a plant suddenly collapses for no apparent reason it is worthwhile examining the roots for the presence of irregular-shaped corky swellings. These are the result of the reaction of the plant root cells to invasion by the eelworms.
Various including begonia, cacti, chrysanthemum, coleus and gloxinia.
There is no effective chemical control so the plant should be destroyed and the pot sterilised before being used again. The best insurance against this trouble is to buy dne’s houseplants only from reputable suppliers.