Only six automaton caterpillars are known to exist and only two of these are studded with diamond, emeralds, rubies, and turquoise as the one for sale by Sotheby's is. This is a fantastically rare, important, and valuable piece. The pre-auction estimates place its value somewhere between $350,000 to $450,000.
From the Sotheby's catalog:
The body realistically designed to represent a caterpillar comprising eleven jointed ring segments, framed by seed pearls, and decorated with translucent red enamel over an engine-turned ground, studded overall with gold-set rubies, turquoise, emeralds,and diamonds. The underside is decorated with champlevé black enamel. When the automaton movement is engaged, the caterpillar crawls realistically, its body moving up and down simulating the undulations of a caterpillar by means of a set of gilt-metal knurled wheels. The automata work is composed of a barrel, cam and two leavers all working together to create the crawling motion.
Here is the Sotheby's catalog listing for the The Ethiopian Caterpillar automaton by Maillardet.
[ Thanks Michael! ]