The fly buzzing round your room, has a life. It's only a little one, and not a very complex one, but the fly is alive. The spider builds its web in the corner, to catch its food to eat; it finds a mate, gives life to offspring. The slug crawling round the garden has a life, and the ants working tirelessly together. The bee bumbling about the flowers and the wasp hunting in the air.
The little lives all live off other lives, of course, just like the bigger lives. The spider and the wasp hunt the flies, and the bees fight off the invaders of the hive just as the lion hunts the antelope and the buffalo attacks the lion that would stalk its calf.
Nature is red in its many teeth and claws, and so it's only fair that the human should take its own part against all the other lives. To kill the wasps that threaten to sting you - even though they'd only do so out of fear, it still hurts; to lay out poison bait for the ants that invade you food stores or the slugs that destroy your garden - even though they only look for food, it is still at your expense; these things are all part of the balance of lives.
But when the ants are only marching up and down outside, why step on them on purpose? When a harmless spider wanders into your home, why smash it? When a single fly buzzes in your window - not defiling your food or crawling on your skin, but only trying to leave - why swat it?
Why do so many people go out of their way to crush those little lives from existence, and even make a joke, a game of it? How do some people find pleasure in killing a helpless, harmless living creature?
Open the window for a confused fly. Carry a spider outside in a glass. step over a line of busy ants. Leave a little life to be lived.