What's happened is that garden spiders lay their eggs in a silk cocoon in sheltered places like your fuse box, then when the spiderlings hatch they tend to group together for a day or so until they get their bearings and disperse. They'll probably wait for a good breeze and 'balloon' away by spinning out a long strand of web to catch the wind.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
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