In the city of Llanelli, which is in the land of the Britons, the people were visited by a plague of flies, like only unto one of the great plagues of Egypt called forth by the Prophet Moses. A huge number of these insects swarmed through the streets, causing great discomfort to the citizens, for it was said that none dared eat with their windows open for fear of this infestation. The merchants of the city soon sold out of the instruments that are used for the killing of these flies but in spite of the fact that the citizens made a great slaughter of them there seemed to be no respite. Some folk ate in their carriages because of the plague and such was the cost of fly-slaying weapons and meals called ‘take-aways’ that some demanded that the council of the city pay them a wergild in compensation. They claimed that these flies had arisen from a site where the waste from the city had in some way been made into new things. Such is the greed of the people, who could not alas see that the plague was brought about by their sins! Eventually the plague died away but the citizens worried that it might return. Nonetheless they had not attended to their own sinfulness.

https://www.walesonline.co.uk/news/wales-news/mystery-fly-plague-descended-llanelli-16365538