 The aliens habit of laying eggs in the stomach (which then burst  out) was inspired by spider wasps, which are said to lay their eggs  "in the abdomen of spiders." This image gave Dan OBannon (qv)  nightmares, which he used to create the story. But spider wasps  (pompilidae) lay eggs on their prey, not inside them, after which  the wasp maggots simply snack on the sting