The Deadly Mantis (1957)

After giant ants (Them!) and a giant spider (Tarantula!), I suppose the next logical step in monster movies was a giant preying mantis.  While perhaps not as well remembered as many of the other monster movies of its era, The Deadly Mantis is, nonetheless, a solid entry in Universal's latter day horror cycle.  It follows a pretty much standard template, with a prehistoric creature frozen in the Arctic ice unexpectedly awoken and subsequently rampaging down the US East Coast.  As with most of these films, the human leads are easily forgotten, but the monster lingers in the memory.  For a B-movie the effects are actually quite impressive, utilising models of the mantis in varying sizes either against miniature sets or matted into the live action.  The effects are weakest when the creature is shown in flight, but when it is on the ground, it is pretty effective.  That said, to humans at least, the preying mantis, no matter how big, isn't the most menacing of threats.

Efficiently directed by Nathan Juran, The Deadly Mantis was to be the first of many science fiction and monster movies he directed, (several with stop motion master Ray Harryhausen).  Of course, the film has the usual problem of credibility when it comes to its monster - giant insects are a physiological impossibility.  Their size is limited by the fact that they breath via a series of holes - spiracles - in their sides, relying upon the natural movements of air molecules to move it in and out of their bodies.  If they grew to the size of something like the mantis in the film, not only would this passive form of 'breathing' be ineffective, but the spiracles would most likely collapse under the weight of their bodies.  Which, of course, is why vertebrates like reptiles and mammals evolved with lungs,  Now, if it had been a mutated mantis, then maybe it could have a set of lungs as part of its mutation and be able to grow to giant proportions...