Way back, I think in the 1960s, the rulers in China got it into their heads that sparrows were eating too much grain every year, so they organised, or ordered, a sparrow killing day. Virtually the entire population of China spent a whole day doing nothing except hunting and killing sparrows by any means available. They killed millions and burnt the bodies on huge bonfires. They thought that this would ensure that next year they would have a bumper grain crop.
In fact, the exact reverse happened, the next year they had the most disastrous grain crop ever. Sparrows don't just eat grain, they are omnivorous, and they eat huge numbers of insects that feed on crops. The lack of sparrows caused a huge increase in these pests, and a consequent crop failure in China.
Nothing exists in isolation. Nature is like a house of cards, remove one and something else comes tumbling down. Not just us, but many other animals depend on the pollinating insects, if they go then a lot more goes with them.
