I spent one summer living in a converted garden shed in the US. It was extremely hot but we couldn't open the windows much due to mosquitos getting in. Fortunately a friendly spider took up residence and started eating them all :) I was very pleased indeed.
Then, one morning, I was asleep and I felt a tickling sensation on my belly. I instinctively swatted at it only to find, to my horror, I'd killed the spiderbro :/ I felt very sad after that, and I got a few mosquito bites for my sins.