Journey into Mystery / Thor Vol 1 #73

Plot

A physicist working at an atomic research lab in New Mexico goes into work one day with a spider in his pants cuff. The creature is bombarded by the atomic rays and grows to a huge size, gaining the power to think and speak, and then attacks the humans. The physicist tricks the spider into snagging a test missile in its web and when it climbs towards it, the missile detonates and kills the spider.