Hannah , Welcome . Yes , they sure do go after the cottonwood pollen , and the willow should even precede that by a few days . They'll be packing it in . It's the resin from the tree buds of the cottonwood that they gather for propalis . There is several variations of the cottonwood which all belong to the poplar family . Ours in Northern B.C. are mostly the balsaam polar , which has a very aromatic resin with several notable medicinal properties . We use it in our homemade cough medicine , which seems to help us when we have a cold . I noticed from another one of your postings that you are an herbalist . Try doing a google search on balsaam poplar and see what you come up with . These trees are an amazing forecaster of rain as their leaves will invert , bottom side up just before a summer rain . Then after the rain is past they fill the air with the sweet spicy smell of balsaam. I am sure looking forward to some warm weather again . It's been quite a cold winter for us , and it's not over yet. ---Burl---