It is a little bit tricky if you want to use wireshark to capture packets on a network interface created by VMware Fusion in Mac OSX. Here are the steps:

Create a FIFO

$ mkfifo /tmp/pcap

Capture packets and pipe to the FIFO using vmnet-sniffer

$ sudo /Applications/VMware\ Fusion.app/Contents/Library/vmnet-sniffer vmnet8 -e -w /tmp/pcap 

Start Wireshark, reading input from the FIFO

$ sudo wireshark -i /tmp/pcap

Remove the FIFO at the end

$ sudo rm /tmp/pcap