The bizarre looking saddleback caterpillar has an effective defense against predators – it is covered with urticating hairs that secrete an irritating venom, delivering a very painful sting that causes swelling, nausea, and a long-lasting rash.
I've been the victim of a similar stinging caterpillar. No saddle, but 2 cm long and lime-coloured. The skin hardens into a scar.
I wouldn't wish the pain on my worst enemy!