The much larger male on top is one very aggressive bee and patrols the Lambsear flowers constantly...looking for trespassers which could be any other bee or wasp and drives them off. They have a reputation for killing honey bees but I have not noticed that so far. The Lambsear flower is used by the female Wool carder for nectar and she also gathers the plant's fibers to line her nest(s). While patroling the flowers the Male will basically pounce on any female and mate for several seconds then release,,,there may be several females coming to his territory and I am beginning to wonder if the females require sperm for each individual egg as I have seen this male mate with several females a couple of dozen times over the past two weeks and this just in passing as I am not studying this activity ..just noticing...