[Closed] Spiders and flies, oh my.

A couple of weeks back, I spotted an odd spider on the stonework outside the back door when I was putting the bin out. Body the size of a pea but long straggly legs, easily over 4" across, maybe bigger. Not one for needless termination of things, I scooped it up in a bowl (it was too big for a pint glass) and hoyed it into the back street.

The next day, either it was back or another had appeared. I ejected this one in the same manner.

The day after that there was two of them. Hmm, I thought. When two became three I figured, "we may have the makings of a problem here" and started swatting them instead. Turned out to be a good idea, as I must've killed over 20 by now. On the upside they do seem to have stopped partying on my door frame, finally.

Now, I appreciate this is probably karma, but I was sat here just now minding my own business when I happened to look up at the window, to find it absolutely covered in flies. Not quite bluebottles, but fat meaty ones nonetheless. I've opened the window and shooed them out, and they seemed to leave quite willingly rather than do that annoying fly thing of zooming everywhere bar an open window. But, they keep appearing in twos and threes. At a rough guess I've got rid of about 40 in the last hour.

So, what the hell's going on? Will it be a plague of locusts next? More importantly, what do I do to get rid of the buggers, is there anything specific I should be looking for? I've scoured the room and can't find anything out of the ordinary, and I've not noticed any odd smells that I'd associate with, say, a dead mouse under the floorboards or something trodden in from outside.

Anyone have any insightful ideas as to why I'm suddenly overrun by crawling things and flying things, and what if anything I should be doing about it?