Grasshoppers are amongst the most ancient living groups of chewing herbivorous insects dating back to the early Triassic period around 250 million years ago. When they are forced to crowd together due to environmental changes, they will transform into locusts which swarm in the millions and destroy crops over wide areas.
This is one of those setups where you have to have some understanding for the killer. Unwanted visitors are annoying on their own, but here are thousands of them all the time. It doesn't excuse the killings, but anyone would be grumpy.