Mimic

Mimic is a 1997 science fiction/horror film directed by by Guillermo del Toro. The monster here is huge, genetically modified cockroaches. This director is a genius, but I'm not a fan of cockroaches. If you're squeamish about bugs, avoid this one. It's horrifying. Who would think genetically modifying cockroaches to help in disease control would turn out bad? Nobody? Well, it turned out bad, And now they're huge and reproducing and killing folks. Not my kind of monster.

trailer:

Moria says, "Mimic does the basics rather well." 1000 Misspent Hours calls it "a monster yarn in the classic style, efficiently told". EW says, "A stylish B horror movie about giant insects in the catacombs of Manhattan, it’s by turns queasy, gross, terrifying, and — never underestimate this one — enthusiastically dumb." Roger Ebert gives it 3 1/2 out of 4 stars and says,

"Mimic'' is superior to most of its cousins, and has been stylishly directed by Guillermo Del Toro, whose visual sense adds a certain texture that makes everything scarier and more effective. It's not often that a movie like this can frighten me, but I was surprised at how effective "Mimic" is.

Rotten Tomatoes has a 61% critics score.