A swarm of flying ants covered Britain, showing up on weather radar as if it were a rain cloud, according to reports.

The UK weather service on Friday tweeted that its radar picked up the 50-mile-wide swarm, covering London and southeast England.

“It’s not raining in London, Kent or Sussex, but our radar says otherwise… The radar is actually picking up a swarm of #flyingants across the southeast.”

A spokesman for the Met Office said there were likely to be "thousands" of ants within the swarm, according to Sky News.

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"On days like today, when it is sunny, the radar detects the swam but we are able to see they are not the same shape as water droplets, and in fact look more insect-like," the spokesman added.

The swarm appears each year on a day that Britons call “Flying Ant Day,” with the Met Office similarly picking up a cloud on radar last year. The phenomenon occurs when young queen ants, followed by males, leave their nests to breed and start new colonies.

As annoying as the swarms can be, the Royal Society of Biology has said that the bugs are harmless and best ignored until they leave. If anything, they may improve soil fertility and help aerate the ground to improve plant life.

The bugs also end up as food for wild birds and other predators.

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One video shared on social media by @WilliamABooth shows a cluster of ants in Ipswich, England, on Friday, FOX 5 reported. The cluster drew hungry seagulls, who delighted in the mass of easy treats.