What are these tiny dark red insects?
These little creatures look a lot like White-margined Burrowing Bug or Sehirus cinctus nymphs. 



Very interesting thing about the Sehirus cinctus is their brooding behavior. The female watches the eggs and even feeds the young for a few days. Have a look around. You might see it.



AFAIK they don't harm your plants.

More info:
http://polyploid.net/bugs/bugs.html 
https://en.wikipedia.org/wiki/Sehirus_cinctus