I just got a couple of Block Erupters for fun, and they are showing in the dev folder as /dev/cu.SLAB_USBtoUART, but cgminer isn't recognizing them.
Check out the tutorial at
http://asics.xgminer.com. You are mixing up your drivers and mining software. You need to either install the USB to UART driver and use bfgminer, or uninstall the USB to UART driver and use cgminer.