What is the difference between a spider and a tick?

a tick is small a spiter is big and ticks are only on dogs and cats

No, ticks feed on many animals from lizards to humans and many in between. If they can penetrate the skin, they will suck the blood.

Ticks do have eight legs, but are not Spiders.

Spiders have a pair (2) of fangs with which they deliver venom to disable their victim. Ticks have one mouthpart with which they penetrate the skin and suck blood. Spiders spin web from spinnerets on their abdomen, ticks have no webs.