Comment by ryannielsen

The "pcapd capability" is iOS's remote virtual interface.

https://developer.apple.com/library/Mac/qa/qa1176/_index.htm...

  OS 5 added a remote virtual interface (RVI) facility that lets
  you use OS X packet trace programs to capture traces from an
  iOS device. The basic strategy is:
  
  1. Connect your iOS device to your Mac via USB.
  
  2. Set up an RVI for that device. This creates a virtual
  network interface on your Mac that represents the iOS device's
  networking stack.
  
  3. Run your OS X packet trace program, and point it at the RVI
  created in the previous step.

If you don't pair the iOS device with the Mac, the technique won't work.