Giant darners are the biggest dragonflies in North America and among the biggest worldwide.   They generally resemble the smaller common green darner (A. junius), with males having a blue-and-black abdomen and green thorax, and females overall green-brown.   Giant darners have a distinctive shape as well, with the long abdomen held in a curve during flight.   They have a scattered distribution in the southwestern US and further south but are nowhere common.   I had seen several over the years, but always in fast flight over ponds and streams.   This one (photographed in Whitewater Canyon in southern California) was also in continuous flight until it caught a male flame skimmer -- a fairly large dragonfly -- and perched in a willow tree to eat it.   I was very pleased to have the opportunity to take pictures, but annoyed at the bad angles, obscuring branches, and the nearly constant wind.   Eventually I managed to get a few reasonable images.