Those teeny tiny creatures are called Aphids and they are a gardeners worst nightmare. They literally suck the life out of plants. Ants harvest them to get at the sap the Aphids take from the plant.
Ladybirds are the solution. One ladybird will eat 50 of these per day.
Interesting fact: Aphids are born pregnant! WTF!
You think your life is miserable, just be glad you're not an aphid. Not only are they born pregnant, they're pregnant without benefit of sex. Not that sex with an aphid sounds like much of a treat. Two things are at work here: parthenogenesis and paedogenesis.
Read more here.