The egg packets are likely to be dropped in the same places as the eggs of the intermediate host, the [[Fleas|flea]]. When ingested by the flea larvae, the oncosphere transforms to a cysticercoid which is infective by the time that metamorphosis is complete. Flea infestation provokes exaggerated grooming behaviour and the cat or dog becomes infected with Dipylidium, when it swallows infected [[fleas]]. Prevention of re-infection therefore requires advice on flea control.
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The oncospheres are within the egg packets. These are ingested by the intermediate host. They develop into cysticercoids, which is infective by the time that metamorphosis is complete.
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Complete development in the intermediate hosts lasts around 1 month. The final host is infected via ingestion of the flea or louse, containing the cysticercoid.