This one is the grandaddy being up to 6mm long, but luckily only found on moles, shrews and small rodents.

Generally fleas that live on diurnal hosts have well-developed eyes; species that parasitize subterranean hosts (e.g., moles or nocturnal animals like bats) have poorly developed eyes or none at all. The most impressive adaptations are highly developed jumping legs and the powerful muscles that control them.