If I am not mistaken these are monarch worms, so to speak. We do enjoy the monarch butterflies that lay eggs on our milk weed, then fly off somewhere, leaving their progeny to fend for themselves.  This fellow and a few of his friends eat the milkweed voraciously, adding length and weight quickly.  I am intrigued by the eye of the fellow in lower left.  Mmm!  All this was yesterday’s delight.