Stephen King's The Mist Wiki has a more comprehensive article on the same creature. For it, see http://stephenkingsthemist.wikia.com/wiki/Scorpion-Flies
Small, plump, flying creatures from another dimension (possibly Todash space), between two and four feet long which swarm over the store windows at night. These creatures have pink, burnt-flesh coloured skin, and their eyes are on stalks protruding from their heads. They have a sting that is lethal, causing the victim to swell up, followed quickly by death.