Never had it happen under a screened bottom. Several years ago, however, I had a stack of boxes on the porch, that I thought had frames in them. One evening, while using the grill that was just a few feet away, I noticed some bees around it. I didn't give it a whole lot of thought, I'm used to bees on the porch investigating equipment that has been taken out of service for painting or storage.
I grill/smoke stuff just about every day, year round. As time went on, it seemed like there were more and more bees around the boxes. Then, one evening I was grilling after the sun went down, and all of a sudden I was noticing by bees flying around the floodlight I have over the grill. 'Huh? Where did they come from?'
I looked at the boxes and saw another one come out of them. Interesting. I put my ear against the stack and tapped gently...sure enough, there was a hum just like when you do it to a full hive. 'Must have picked up a swarm.'
They weren't bothering me much, so I left them for a while. Then there came a day when I decided I needed to check on them...I tried to lift the top box...nope, not budging...none of the four boxes would move, I tried twisting them one way, then the other. No luck.
Well, I had to get in there, I tried to loosen them up with a hive tool but didn't get far so I got a bigger carpentry tool and a crow-bar. Eventually, I got the boxes apart. It was a big mess, honey everywhere, they'd built combs right down through and all the combs ended up broken off and laying at the bottom of the stack.
I figured they were goners, but just for giggles I left two frameless boxes full of brood and stores jumbled at the bottom and stuck three boxes with frames over the top of them with a proper inner and outer cover. About 6 weeks later I opened them up- the comb at the bottom was empty and dry, they'd moved into the frames above and were booming.
I left them alone for the Winter and in the Spring I supered them. They were my most productive hive that year, giving me nearly 200lbs of honey.