idk I'd feel bad stepping on a snail...maybe it's the size or the crunch. But smaller insect ye i dont care.

I feel awful when I step on a snail. But stuff like gnatt flies, it's like I've given your friends so much leverage letting them out and now you're taking advantage by breeding in my plants and flying into my nose

I think there are two main reasons:

1. insects don't emote in a way we can perceive. The ones that do typically express it by secreting some kind of chemical which we either can't perceive or can't intuitively interpret. So if it's in pain, we can't really tell.

2. a lot of insects pose a challenge to our own survival. For example, insects getting into our food can make us sick. Some insects spread disease by contact or biting. This has caused humans to develop an instinct to fear, avoid, and/or kill insects on sight.

I think there is a difference.

Basically all animals will attack other animals when they invade their home space. Even insects do so and it can be brutal. Speaking outside of human moral constructs, you wouldn't be out of line for killing a rat or even a cat that was unwelcome in your home. Life will do what it can to ensure survival.

But it's easier to feel empathy for what is more similar to us. So, mammals, for example. Domesticated and tame animals that have adapted to humans.

I suggest making small efforts to cultivate compassion even for the creepiest insects, by taking a cup, bowl, or piece of paper and taking them outside. Now it could be argued whether this is doing them any favors, but I feel better about that compared to just smashing them.

It may sound ridiculous but yes I did reach the point where I am affected by any life I take, and really strive to avoid it where possible. I have "mutual arrangements" with a variety of insects in my house, such as small spiders. They stay out of my way, and I let them take care of other insects that slip through the cracks.

Probably because most invertebrates are not known to be sentient?