Resin bees nest in cavities using resin pitch from trees to close off their nesting tunnels. When opening nests in the fall and you see small pupae between walls of resin, close up the nests and bees will emerge the following spring. If nests are empty proceed as noted by Kat B.
“Dear Dr. Dogterom,
Thank you for your response!
After some trial and error, I found the best way to clean the resin was with boiling hot water. I submerged the trays in the water and let them sit briefly to allow the resin to soften. I then scraped each channel clean using a small screw driver wrapped in cotton gauze. The material picked up the sticky mess and I adjusted the wrapping as I went so that I did not simply redistribute the mess. A very light residue remained, but was no longer tacky after cooling. Overall this process was very effective and fairly efficient – I had quite a few trays with resin, but was able to quickly clean them. I found it best to work with two trays at a time. Sincerely, Kat B. 🐝