The scourge of the aphid
or more specifically, from your description, the blackfly the bane of rose growers globally. Looks something like this:
Aphid control, how to get rid of Aphids.
Some tips in the above link too.
You should be able to get some insect larvae that will eat them all and their eggs when introduced into your garden, people in the US release Praying mantis and Ladybirds.
In the UK we use these:
Just Green Just Lacewing Larvae - From £16.00 - Just Green Check the bug houses that will ensure a good population for years to come. Some of these bugs if encouraged will return year after year multiplying and therefore keeping down the aphid population. The non flying larval stages of the ladybird bug and lacewing are preffered as they dont fly away.
There are various natural and chemical bugsprays that will work too, just be sure to get something that kills the eggs too. Also check the stickies for a homemade organic bug spray recipe I saw somewhere. One teaspoon of dish washing detergent in a litre or two of water, sprayed will kill mosts of them but may not kil the eggs.
Meanwhile in my garden I have 12 holes to dig and over 150litres of compost to shift several miles before my next seedlings are ready to go outside. I just wish I could get some of those bugs to keep the mozzies off me!!
Keep it green.