I've posted this before, I hope it helps.
Make a solution of 1 quart 80% alcohol (a higher concentration will evaporate too fast), 1 ounce peppermint oil, ~1 teaspoon dishwashing liquid.
Put the mixture in a spray bottle and go at it.
The alcohol will dehydrate and kill on contact many insects including spiders and mosquitoes. I do not appreciate mosquitoes. Spiders and many other insects taste with their feet and the peppermint oil will discourage new residents. The dishwashing liquid (Dawn or equivalent) helps make the solution stick.
I routinely spray down my entire coop every few weeks during the warmer months. Unlike many pests, I think the minty odor is quite pleasant.
Though spiders do eat mosquitoes. I got a ton that live in my house and I hardly ever see flies or gnats, even though there's a bunch that buzz around in the summer and a few in winter.
