About changing size, according to Mike Orlove: 

 Young adult carpenter bees appear to "grow" toward the end of hibernation when their air sacs inflate. In certian locations the bees vary in size as adults. In Maryland they tend not to vary; In Ithaca they do. People who live in different locations end up arguing about this.  In a mature nest with a brood of twelve (a good year) there is always one grossly oversized female (adapted for long-distance dispersal up to 120 miles), one grossly undersized male (built for being a back door man) and just one male who is about the same size as a normal female. There is a link in the article to a paper by Barthel amd Baird about the influence of male size on reproductive success. (He's in Oklahoma.)