Immortal Vespula?

Dec 10, 11, 12 overnight lows were 19, 18 and 21 F. Today a week later at 5 PM as the sun was disappearing I counted 11 yellowjackets flying into their ground nest in 60 seconds. Amazing. They should have all been dead a month ago. There should not be insects out for these wasps to feed upon.. maybe they are going to get water? I entered via the new North Gate - lots of poison ivy sprouts there to keep trimmed down. I yellow-flagged a trail from SW Trail post #5 northeast to the Big Trees by the East Pond, a route through dense young green ash and patches of willow.  Just one deer spotted but robins (by the score) and starlings were gathered in the Woods in raucous crowds. They suddenly fell quiet around 4:45. Claire appeared hiking out with her traps.