Insects never have more than three pairs of jointed legs.
Scorpions, spiders, mites and ticks have four pairs, at least when adult. Scorpions have jointed abdomens but the other three do not. Mites, such as chiggers and chicken mites, are generally much smaller than ticks. A tick must get blood from some animal in order to exist, although some may live for a year without it. Before feeding it is round or oval, and quite flat.