No. "Cluster Flies" are a phenomenon on their own, not associated with dead bodies.They swarm in roofs at this time of year, sometimes over several days. They do not carry disease, and are harmless but a cussed nuisance. We have suffered them over several years now, and they seem to be impossible to eradicate. I leave a large electric Pest Control fly killer unit on in the roof all the year round, which keeps them at bay for all of the year except now. I thought in fact that they had gone this year, but no, in the last week swarming on two days produced something like a thousand electrocuted bodies of the blighters.