Interesting, but I do think that what you saw was a Tomato Horn Worm that had been parasitized by Braconid Wasp Larva. Once the wasps young have finished eating the caterpillar's muscle tissues they burrow out through the THW skin and spin a small cocoon in which to complete their metamorphous. After the wasp young mature and leave, their cocoons fall off and all that is left of the THW is an empty brown husk, hence the skeleton of the THW that you saw.I use DE on my tomato plants and it kills the tomato worm. All that is left is the skeleton....
If Diatomaceous Earth is actually an insecticide, for it to work on THW it would be necessary to pile DE up to the top of your tomato plants because in order to work DE must come into contact with the target insect, the Tomato Horn Worm in this instance. Also because the THW is the caterpillar phase of the Sphinx Moth, the female moth lays her eggs high up in the tomato plant so that when her eggs hatch, the growing caterpillars will have a ready source of sweet, tender, succulent, and nutritious tomato vine on which to feed. If you spot a THW in your garden and it has tiny rice like capsules on its body, do not disturb it because if it is not already dead the damage the Braconid wasp larva have inflicted has caused the THW to stop feeding. You want every one of these tiny non stinging wasps to grow up to target more THWs.
http://www.organicgardening.com/learn-and-grow/how-to-control-hornworms