Fungus gnats? They like moist conditions with readily-available organic matter, aka your worm bin. In small numbers, they’re mostly annoying. In large numbers, they can do some serious root damage.
This thread is a good discussion about how you might deal with them, and there’s a GrowFAQ entry about biological controls as well.
Not a lot of pictures in this FAQ entry, but there is a pic of an adult fungus gnat.
Assuming they are fungus gnats, they’re not the end of the world, and won’t ruin your plants overnight (or even in weeks). I managed to purge them last winter without immense difficulty.