mimic (1997)

one of the entomologist creates a new insect to kill cockroaches but everything doesnot go in the way it is expected.new creature goes into mutation and hides in underground of the city.It grows and kills people.There are some irrational scenes like a woman may be caught by a big insect with its wings and nobody sees even cameras.Sometimes you may have to force your logic to make yourself convinced about plot.It is worth watching though.Nice part is insects mimic people and they start mimicing insects

http://www.imdb.com/title/tt0119675/