[ noun ] a regional term for `creature' (especially for domestic animals) <noun.animal>
critter \crit"ter\ (kr[i^]t"t[~e]r), n. [from creature.] [Also spelled {crittur}.] 1. Any animal; as, lots of critters come out only at night. [U. S., western dialect] [PJC]
2. Specifically: A domestic animal or a non-predatory wild animal; -- contrasted with {varmint}, also dialectal. [U. S., western dialect] [PJC]
The disease is carried by the Ixodes dammini, commonly known as the deer tick, a tiny but tough critter that lurks on grass and leaves.