is there an easy way to verify that a given iOS app is using https for its connections? For example, can I verify that the Facebook or Twitter apps connect via https?

I know I could use a packet sniffer but that's not "easy" for me.

I googled it quickly on your behalf

I'm not familiar with iPhone internals, but given the way everything else of theirs is designed, I cannot find that there is a central dashboard for enforcing this.

That said, many apps that use OAuth (Facebook, twitter) will be running over TLS1.x, and many more will pop up a notification badge saying "server identity could not be verified, continue?" with a yes/no choice. Apple has (allegedly) installed most root certs from trusted certification authorities, so if the app or service is "secure," the app that calls that API should be as well.

That said, if you're being proxied (so, basically any enterprise hotspot ever), you could still be man-in-the-middled.

What are you specifically worried about?

Not worried about anything specific. I just seem to often read that iOS or Android app X was recently discovered to be sending things in the clear, and it made me wonder if there's a way to check the apps I have installed.

I Googled too - didn't find anything and thought I'd ask around here.

If you have a desktop around on the same WiFi, install a proxy server and use it from your iOS device (in the network settings you have HTTP Proxy settings).

I'm using http://www.charlesproxy.com/