If grasshoppers broke into an anthill like that in real life, the ants would tear them apart.
Which they kind of do at the film's climax.
Any viewer will response to Hopper's speech about "keeping those ants in line" will involve this. At first, you think he's literally talking about ants and grasshoppers, but at some point you'll inject your own beliefs into it, and at some later point, you'll realize EVERY viewer injects their own beliefs into it.
At the end, if you look, you see Molt dodging into the grass, not flying away, so he's not actually abandoning his brother. Just another feature that shows he's not evil. But at the same time he literally 'jumps out of his skin'. He's shed his old life. Now he can be a good guy, and become the Strong Man of the circus!
Why did Hopper fall for Flik's Batman Gambit at the film's climax and mistake the real bird for another fake one? Well, Flik probably knew that, because of his Villainous Breakdown, Hopper's rage had blinded him from realizing the true terror of the situation until it was too late.
Fridge Horror: Remember those three grasshoppers that Hopper buries with the grain, and when you were a kid you thought that they crawled out at a later time and flew to the island? Guess what? He fucking killed them.
This one could go either way, really. Given the oft-ignored Square/Cube Law, a real grasshopper would probably survive that. However, it seems perfectly in character for Hopper to carelessly kill them like that.
Carelessly? No, that was quite deliberate.
Also, the fridge horror only works if you actually thought they survived. This troper never saw this scene as anything else than outright murder. Of course, if you start bringing physics into this movie, lotsa stuff starts making less sense. Like Flik being afraid of falling down the cliff when ants are so small they'd survive a fall from any height and so on.
Hopper not killing Molt because of a deathbed promise to his mother might seem like a redeeming feature, right? wrong! Notice how when Molt keeps annoying him he brutally attacks one of his gang that was just standing there. Given his murderous nature it's quite likely that he attacks, and possibly kills anyone that's on hand when Molt annoys him, in other words what would normally be a redeeming feature just makes him more dangerous.
Rosie is a black-widow spider. She makes reference to her 12th husband dying. note It's the norm for female black widow spiders to kill the male after sex. Sure, that doesn't necessarily imply that it's the reason he died, but still...
Is that even really a pun, given that the expression Black Widow came from the spider in the first place?
Ever notice how one of Hopper's eyes is more cloudy and scarred then the other one? In one scene Molt mentions how Hopper was once attacked by a bird. During the climax, Hopper reacts badly when he thinks the bird plucked out Slim's eye. This paints the image that Hopper is so scared of birds because he almost lost his eye to a bird.
A little of both: remember those terrifying dinosaurs from Jurassic Park? Most of them died out millions of years ago, sure, but the ones that didn't are still around; they just got very small (and grew more feathers). At the appropriate scale, they can be just as scary.
Now that Flik has industrialized his colony, how long will it be before the ants overharvest and deforest (degrass?) the island?