What type of worms are these?
This is a fungus gnat larvae migration. They are not parasites or worms.
Fungus gnats lay their eggs in moist soil, and their eggs hatch into larvae that eat fungi in the soil. They are not a problem. The ones in your photo will either die or enter the soil under the concrete. No treatment is necessary.
Occasionally in some years, we'll have the exact weather conditions that favor their growth. Then may be sightings of a fungus gnat larvae migration. It's an interesting phenomena, that's all. No cause for alarm. You can see plenty of photos in a search online.
Here is more about fungus gnats from our website: http://extension.umd.edu/hgic/fungus-gnats
This is a great photo! We've never seen them migrate in a circle. If you have close-up photos, we'd love to see them.