It's not unheard of for some species of spider to migrate indoors during warmer months. Peppermint and lemon juice is usually a decent repellent. But, you don't generally see species of that size in this area. Not outside of the Forest, at least. And, anything living in the Forest wouldn't need to come to the greenhouses for cooler climes.
Give me a few minutes and I can come down to help you out.