Interfacing AVRispmkII with avrdude on OS/X ... driver required?

Hi, not sure if this is the right place for this ...

I just bought an AVRispmkII as an alternative to the USBtinyISP. Unfortunately, it simply isn't recognized by the Mac. It is, to an extent:

So electrically it's OK. But if I do:

ls /dev/tty*

There is no change to the list, whether or not it is plugged in. And the green indicator LED just flashes briefly and goes off.

One web site suggested installing the Silicon Labs device driver, which I did, to no effect:

https://www.silabs.com/products/mcu/Pages/USBtoUARTBridgeVCPDrivers.aspx

The documentation from Atmel just says to install the software "under Windows" which isn't very helpful.

Does anyone know how to get it working on a Mac?