The saddleback caterpillar makes it easy for you to spot and avoid touching it with its ridiculously bright coloring. And trust me, you'll be glad for the help in seeing and keeping away from this think. The fleshy horns that sit puffy-piggy-tail-like at each end of the body are covered in hairs that secrete venom. Brushing up against them causes pain as strong as that from a bee sting, swelling, nausea and a rash that will last for several days.
Though the puss caterpillar wins for most venomous caterpillar in North and Central America, the saddle back comes in a very close second.