fish schools:

https://www.youtube.com/watch?v=cIgHEhziUxU

starling flocking:

https://www.youtube.com/watch?v=QOGCSBh3kmM

bees:

https://www.youtube.com/watch?v=vkMoRoiKmdM

swarm simulation:

https://www.youtube.com/watch?v=HSwragUai7Q

stigmergy:

https://www.youtube.com/watch?v=uOmRwDLsdXk