"When dry, the Dipylidium caninum segments look like "cucumber seeds", and the Taenia segments look like "rice grains." These egg packets may be seen on the pet's anal area and in their bedding.
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The life cycle of Dipylidium caninum, the "cucumber tapeworm," involves dogs or cats (humans rarely) as the definitive host and fleas or lice as the intermediate host. The perianal region of the dog or cat becomes contaminated with eggs when the eggs are passed in the feces, and the flea or louse ingests the eggs. The dog or cat (or human) is infected when they ingest a flea or louse infected with the metacestode state (cysticercoid) (view a diagram of the life cycle). Hence the importance of controlling fleas on your pet!
The feces of an infected dog or cat (or human) may contain proglottids (often referred to incorrectly as "segments") that are shed from the tapeworm, and these have a characteristic size and shape (more like rice grains than cucumbers). Diagnosis of this species depends on finding proglottids or "egg packets" (see below) in the feces. (The proglottids of the other common tapeworm of dogs, Taenia pisiformis, are much larger and rectangular in shape.)