You mention "composite", so ....
you could use the alpha-over composite node where your ants (represented here by small cubes, but if in motion you'd want a video of the bugs moving) appears on top of your rendering (could also be a video of your moving hand):
It would look as awful as one of those cheap 1950's movies or as laughable as the spider crawling up James Bond's arm in Dr No:
If you want realism, you'd have to do some modeling in blender and then perhaps some form of Particle System rendered as objects that are modeled as crawling ants -- might look better.