What do the words "churn, pre-8th century and buturfliog" means in these 2 sentences?

Well, these beautiful insects do fly, but they aren’t made of butter and they certainly don’t eat or churn butter either! Many of them do, however, bear the color of butter and many think that their name is derived from the original pre-8th century word buturfliog (butere being butter and fleoge being fly).