Those are aphids- a lot of aphids. In my experience, usually, a methrin based insecticide spray (resmethrin, permethrin, and others) is inexpensive and will kill the aphids but I don't have experience with using that on a fern. You can try the spray on a small part of the plant to watch the effect of it before spraying all of the plant.

I have the same on my fern. I rinsed them down the sink.

http://houseplants.about.com/od/pests/a/Aphids.htm