Smaller than a dog tick is a deer tick. Smaller than a deer tick is a deer tick nymph. The nymphs are the ones most people get Lyme Disease from (like me just recently) because they are easily missed. But even smaller than a deer tick nymph, is the ridiculously tiny deer tick larva. I found this one on my ankle last night. A ruler showing 1/16th inch lines is there for comparison. (Larvae = plural, Larva = singular).
If you manage to see one of these ticks (it helps if you have lily white skin), how do you know if it's a nymph or a larvae? If it's late summer/early fall odds are it's a larva. My rough guide is that if it's so small you can't see the legs without a magnifying glass, it's a larva. That might not work for everyone. So here's another way: The larvae have only six legs, while nymphs and adults have eight. You are going to need a magnifying glass to see this. Here's the one from last night (taken through a magnifying glass). Note that the long mouth parts are not legs.