Faux Symbolism: The roaches are called the Judas Breed, and there's some Christian imagery scattered across the first movie — but it doesn't amount to much in terms of meaning, and is probably there because del Toro likes creepy religious imagery (see Cronos).
Fridge Brilliance: The use of termites and praying mantises as the base components for the cockroach-hunting Judas Breed actually makes a lot of sense. Firstly, mantises are not only voracious hunters, but also one of the predatory insect species most known for biological mimicry — flower mantises, leaf mantises, bark mantises, etc. Secondly, termites are not only closely related to cockroaches (technically, termites are cockroaches) and mantises, but also make heavy use of chemical weaponry, just like ants do. So taking a praying mantis and splicing in termite DNA is actually a relatively plausible way to get a roach-mimicking mantis that can also secrete roach-killing chemicals... y'know, by Mad Science standards.
Fridge Logic: Given that the bugs started out so small and are living underneath New York City, wouldn't it make more sense for them to adapt to mimic and consume rats than humans? Taking up such an ecological niche wouldn't even require them to evolve lungs, because there already are insects as long (though not as heavy) as rats.
Leonard notes that the rats are all gone in the subway, so they may have been the appetizers until the bugs moved up to humans after exhausting the rat burger supply.
For that matter, why aren't they too busy eating each other to bother pursuing humans? Preying mantids eat one another as readily as any other insect prey, and termites from different nests kill each other on sight.
They're colony/hive-minded and they all originally bred from that hive.
Funny Moments: Most of Leonard's lines, particularly his acerbic banter with Peter.
Peter: Have you ever seen anything like this before? Leonard: Have I ever seen any shit like this before? Do I look like I've seen any shit like this before? Hell no, I ain't never seen any ''shit'' like this before! Who the fuck would wanna climb up these walls and hang one of these? Musta been some elephant-ass motherfucker - I don't know who the fuck...
Nausea Fuel: At one point the team of Leonard, Peter, and Josh stumble into the waste chamber of the bugs (which is actually Truth in Television for underground colony nesters such as ants and termites). An entire room of...hanging bug crap. The subway cop repeatedly lampshades it, ending with a Cluster F-Bomb about "who the fuck would want to crawl up there and lay shit like that?"
