Capillaria plica is the scientific name for the bladder worm. Capillaria plica may infect the urinary bladder, and occasionally the ureters and renal pelvises, of dogs and cats. Distribution is worldwide, and wild animals appear to be the primary hosts.
A similar but less common organism, C felis cati, is also found in cats. Dogs and cats become infected by eating earthworms that contain the first-stage larvae. Mature Capillaria are threadlike, yellowish, and 13–60 mm long. The eggs are colorless, operculated, have a slightly pitted shell, and are 63–68 × 24–27 μm in size.