aha here’s a full explanation of the thought process:

• no other weather report matches these patterns
• they’re suspiciously round and not blobby like real clouds
• they’re each suspiciously localised around the radars in the network
• there are lots of types of radar artefacts, including close-to-radar ground-clutter (this is what I assumed it was) but it’s too consistent and large of a signal for that
• so it must be something uniform, in the air instead of on the ground, that isn’t rain
• bugs are about the size of a big rain drop! enough to be picked up as a strong signal by the radar and enough to prevent the radar from seeing long distances
• It’s also been flying-ant-day recently across Europe