How can I see 127.0.0.1 traffic on Windows using Wireshark?

If you are trying to this on a Windows computer, unfortunately it is not possible out of the box. You will need to install some additional software that will capture data on the loopback interface.

On a Linux computer, you will need to capture from the loopback interface which is lo most of the time. Most other Unix operating systems use lo0.

To keep this current, as hsluoyz said, install npcap

http://wiki.wireshark.org/CaptureSetup/Loopback

When installed on Windows Vista or later (including Win7, Win8 and Win10) with option "Support loopback traffic ("Npcap Loopback Adapter" will be created)" selected, it will create an Npcap Loopback Adapter that can be selected in Wireshark so as to capture IPv4/IPv6 loopback traffic.

Although you found the answer before I could respond, you can also use Socket Sniffer, which looks at Winsock calls and monitors network sockets; the download link is at the bottom of the page.