That sucker that has been eating your tomatos is the Tomato Horn Worm, and those things on its back are not tomato seeds, they are the cocoons spun by the larvae of the Braconid Wasp.
The adult wasp laid the eggs inside the Horn Worm where they hatched and grow as larvae eating the worm from the inside until they emerge through the skin and spun these little cocoons. It is really a marvel of nature, the DNA of the wasp actually contains portions that are the templates for the components of viral particles, which when assembled into viruses by the wasp, suppress the immune system in the worm and allow the parasitoid to grow inside the host undetected.
As difficult as it may be, you shouldn't kill the worms with cocoons as the wasps they are nurturing are an important biological control agent. By killing the infected worm, you also kill the wasp larvae thus reducing the predator population and increasing the worm population. You can put the worm in a jar with fresh leaves for it to eat until the wasps hatch then let them loose in your garden. By the time you see the cocoons, the worm is dead - he just doesn't know it yet...