Came across a good cheap one while on a visit to an apiary this year.
Have no photo but will try and explain. He was using it to guard his nuc's.
It was made out of a plastic 2Ltr soft drinks bottle and a length of white 3/4" plastic pipe.
Just below the neck of the bottle he had cut out 2 holes one either side just big enough to take the pipe. The pipe was 2" longer than the width of the pipe and had 3 holes drilled in it one in the center and 2 just out from it. Just far enough not to be outside the bottle. This pipe was inserted into the bottle with 1" of pipe either side and the holes facing downward, he had hot-melt glued them into place.
All that was to be done then was to fill them to within 2" of the pipe with some dilute orange drink (cordial) or drop of wine, beer etc and place near the hive/nuc to be protected. They simply crawl into the pipe then make there way into the holes following the smell and cannot find there way out. They become tired of flying and fall into the liquid to drowned. There was hundreds caught in his traps which I think would have caused damage to his nuc's were he not employing this trap to help the bee's. Interestingly there was no bee's to be seen in them traps just wasp's and flies.
I think I will be making a few of these for next year. Another devious traps out there or scent to draw them in.
Also would be interested to here about and see images of what enemies your bee's have to endure. IE: insects, mammals
Mine have to contend with European Paper Wasp, Mice, Wax Moth, Pine Martins, Mink