But the ones we've got have another piece of screen on it I recall.  

 
Yes, I agree, the one in the picture appears damaged and missing an excluder
grate (on the top half) and it is setting upside down as to how it would set
on the bottom board entrance in use. From the old books, it is called a
drone trap. It works well to stop a first swarm as the other's have stated.
The original purpose was to reduce the number of drones (freeloaders) from
not so perfect natural drawn comb back before foundation was plentiful. One
of the ideas in that day was that swarming was related to the number of
drones in a hive. I am not sure of the exact numbers, but over a certain
percentage of drones in the general population was expected to trigger
swarming (hive senses they have a failing queen). Managing drone flights for
mating purposes was also one of the original uses. I suppose using it to
collect drones for insemination is something it could be used for today
though I don't know if anyone makes them anymore. The ones my grandfather
left me, the cones are rusted out and broken down.

Roger Wood
Independence, Mo    

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