The main difference between fleas and ticks is that fleas are insects with six legs while ticks are arachnids with eight legs. Ticks are bigger than fleas with average measurements of 1/8 inch to 1/4 inch. Fleas are half that size measuring an average of 1/16 inch to 1/8 inch.
Both fleas and ticks are parasites that feed on a host, but they implement this in different ways. Fleas choose one host as adults and remain there until they die. They lay twenty to forty eggs at a time throughout their life span. Ticks choose multiples hosts throughout their life span and feed as larvae, nymphs and adults. At the end of their lives, they detach from their host and lay thousands of eggs at one time.
Fleas have few hosts generally limiting themselves to cats and dogs. They can also be found on raccoons, opossums, coyotes and foxes. Ticks are less picky about their hosts and choose anything from birds, snakes and lizards to foxes, deer and humans. Like fleas, they are commonly found on cats and dogs.
Fleas prefer warm climates and are frequently found on indoor pets. Ticks are more resilient and prefer cold temperatures making them harder to kill. Fleas commonly transmit bartonellosis and tapeworms. Ticks transmit potentially deadly diseases such as Lyme disease and Rocky Mountain Spotted Fever. A flea's life span is approximately 100 days. A tick can live anywhere from three weeks to three years.