Linux has an internal usb monitor called usbmon.
If you want to use it please read the documentation file:
linux/Documentation/usb/usbmon.txt
After selecting a bus number to sniff and generating the log file, just rename this file to something.mon and use vusb-analyzer to visualise it.
Download vusb-analyzer here:
http://vusb-analyzer.sourceforge.net/
Alan C. Assis 