28mm scale ant swarms

[Photographer]

Like what was suggested, use fine-grain sand painted to match the ants.

@ Photographer: what a horrible way to die.

[Sheerluck Holmes]

An answer is cous-cous. Thank you Igniateff.
I have made 4 swarm bases up to now on 60mm round mdf bases.
One is a plain swarm, one a swarm eating a man, one a swarm pouring over a log and one a swarm stripping a small tree; thanks to everyone that chipped in.
Whilst cous-cous is well over scale it works visually as a boiling mass of creatures.
Very simple to do, happy to detail the process.

Any chance of a photo to see what it looks like?