Following the drilling attempt, a hole has somehow opened up in the wall which allows Quatermass and the others access to the interior chamber. There they find the remains of insect-like aliens resembling giant three-legged locusts, with stubby antennae on their heads giving the impression of horns. As Quatermass and Roney examine the remains, they theorise that the aliens might have come from a nearby planet which was habitable five million years ago — Mars. (thetvdb.com)