This is a Red-Footed Cannibalfly (Promachus rufipes), eating a Common Green Bottle Fly (Lucilia sericata). They feed on bees, wasps, dragonflies, spiders, beetles, grasshoppers, and other flies. They have a venomous saliva that allow it to easily subdue prey that may be larger than itself. The saliva contains chemicals that dissolves the inside of a victim, in preparation for them to be sucked out. They are also known as; Robberfly, Robber Fly, Assassin Fly, or Bee Panther.