My husband and I recently added interior feeders to our two hives in hopes of eliminate robbing. We had been using exterior feeders and noticed some very aggressive black bees not letting our bees even close to the syrup. (as well as yellow jackets)

We opted to use the jar feeders (easy fast build, thank you AKDan). We had planned on adding multiple jars to the one hive so used a large square of screen. We decided the solid wood base would hinder ventilation so left one side off. We have noticed the bees congregating under the screen. I'm assuming they are cooling off (or trying to go up?), however I've never seen screen used in place of canvas. Are there any concerns we should have?

Also, how long before they catch on and start using the new feeders. We are concerned because there is limited access over the bars and the syrup hasn't gone down in over 12 hours.

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Edited to add: We noticed in the picture that the bees are starting to pull the threads on the canvas. This could be a disastrous. We will try to flip the canvas and screen over so they can't get to the raw edge. They are sewn together.