Answer: Since the bees have already built a nest, it's likely that there is only one entrance and exit hole. If you can examine the entrance/exit of the nest to see how far below the deck it is, you might be able to starve the nest out by placing a barrier over the entrance of the nest. Wait until after dusk and see what you can see with a flashlight. Try not to direct the beam of light directly into the opening (you may alarm the residents). If you can cover the opening with foil or a plastic baggie, you'll be able to trap the insects in the nest. If that's not possible, you may be able to use a spray (there are several bee/wasp nest killers on the market and you can stand at least 10' away while you spray). Saturate the hive to the best of your ability and plan to repeat this process if you don't get them all with the first treatment. Nighttime is the safest time to attack the problem. Or, if you have patience, you can simply wait them out - they will die out over the winter months and that should take care of the problem.
Good luck with your project!
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