Sort of adds a new twist to "stinger service."
I have the same issue, only here it's wasps. Boy, do they get upset when you take the cover off the panel .... or open the light to replace a bulb, or ... well, you get the idea. It's especially fun when you're 20-ft. up a ladder.
Spiders are fun, too .... try to remove the cover from a splice box, and there are those little fuzzy legs pulling the cover back on ...
Enclosure wars? Sometimes the spider wins, sometimes the wasps. Bodies remain as evidence.
Which is why I seal EVERY little opening, apart from the little 'drainaige' seams at the bottom of some enclosures. A bit of tape on the inside .... though, for sealing a mast I'd go with spray foam at the weatherhead. They even make it in black (find it where you get pond supplies)