A Lovely Day to Be a Bee

Despite the fact that the internet claimed the temp was only 50 degrees F, the honeybees were making hay while the sun was shining, bringing in loads of a pale yellow pollen that I do not recognize.  What blooms here in March besides dead nettle and crocuses?  (and yes, the bees were on the crocuses, but that pollen is not pale yellow, nor are my 7-8 blooms nearly enough for the hundreds of busy bees returning to the hive with their baskets full).  It is supposed to be even warmer tomorrow, and I am contemplating a quick peek in the hive at the hottest part of the day, so I can lay some feed on the top bars.  On the other hand, I don't want to mess with something that seems to be working.  I know better than to trust this bit of Spring we are having, though, since it always snows in April at least once (and generally when I'm trying to install new beehives).  It would break my little heart if they starved at this point, since they are working so hard to survive...