Jerry's experience when he wanted "perfect" exclusion is fascinating.  Yes, I should have admitted that the cones (plastic or the stainless screen cones that we now use) are not "perfect" excluders, but hardly anyone wants or needs them to be perfect.

We knew they were not perfect as occasionally one sees a bee inside a hive with full baskets of pollen.  If the cones were perfect excluders that could not be.  Frankly, our biggest challenge is convincing beekeepers that they will not harm their hives by trapping pollen (mainly because some catalogs advise beekeepers to not leave their traps open for more than a few days), so we never get to the point of admitting that a few bees get back in through the cones.

Please consider that when used in a pollen trap, or as a one-way escape for bee removal from a house, etc., the bees deliberately have an alternative place to go.  In the case of a pollen trap, they can enter through the entrance that strips their pollen.  In the other case, they have a nuc/hive placed nearby with brood.  If the bees did not have such alternatives, I suspect that a very large percentage would get back in via the narrow end...as Jerry reports.

Lloyd
www.rossrounds.com
Lloyd Spear, Owner of Ross Rounds, Inc.
Manufacturer of round comb honey equipment and Sundance pollen traps