In a large, deep pot simmer some (not all) of the garlic in olive oil for a minute or two, just to release the sweetness. Place the crabs in the pot and pour over them one at a time; the beer, the rest of the garlic, old bay seasoning, and the parsley.
In the meantime, cook the pasta in rolling boiling water until al dente (slightly hard). When the crabs are bright red all over, remove them from the sauce and set aside. Drain the pasta and finish cooking it in the beer sauce (the pasta will soak up the hops and garlic flavor this way). Serve the pasta with the crabs sitting on top.