Flies

 Yes, flies.  MILLIONS of them in the roof room this year. Not normal houseflies - much, much smaller than that.  Cluster flies they are commonly called.  Very small indeed but under the microscope they look like normal houseflies.  Wings, big multi-faceted eyes, head, thorax, abdomen.  Flies alright.

Each autumn we get them inside the roof room but the problem has increased year on year.

The roof room sits in what was a water tank.  Over time a layer of pond-like vegetation has accumulated on the flat fibreglass surface of the roof inside the tank.  It drains only slowly towards the south west corner of the tank, then down the tank's huge outlet pipe.  In effect we have an increasingly tempting pond in which flies will thrive in due season.

As winter approaches they seek somewhere sheltered and warm.  Wouldn't you?  Conservatories, greenhouses and roof-rooms are ideal.

We are careful to keep the sliding glass doors and the window shut to  minimise fly access in the autumn but still they get in to what amounts to a very well sealed box.  This astonishing picture illustrates the scale of the problem this year:

It shows the roof room floor at its north east corner.  The circular clear area is where a vacuum cleaner had been standing.

Two possible solutions came to mind:

1. a fine mesh fly-screen over the sliding doors.  That could work IF that was the entry route taken, which seemed unlikely for flies in such numbers.  Expensive too - the salesman's price fell from £3,000 to £1.500 as there was a special offer on.  Quel surprise.  The salesman admitted though that he had never seen anything like this.

2. call in pest control people.  £200 upwards, guaranteed for three months.  'Easy' they said 'We'll  smoke them out'.  Hmm.  Most were already dead!

For the fifth time this autumn we vacuumed the room and its surfaces clean of flies.  Yet overnight a few more dead flies appeared on the floor areas - mostly below windows.  Towards the tops of the windows cluster flies were dancing about.  The ones on the outsides seemed to be dancing upwards, towards the flat roof overhangs.  Those inside were also dancing, or desperately trying to escape maybe?

By then I had taken the pest controllers' hint and bought half a dozen smoke bombs - small stubby fireworks, 11g size.  I measured the volume of the roof room and landing which called for two of them - simply put them on upturned plates or baking trays, light them, impressive smoke, lock-up and leave for three hours.

In fact I left it overnight.

Next morning the floors had collected more flies, all dead.  NO remaining flies dancing on the insides of the windows but still plenty dancing outside.

Conclusion? Flies are desperate to get in.  Once in, and with a life span of just two or three days anyway they are doomed.  

Question?  How are they getting in to a sealed box? I got a clue when changing the battery on the roof-top weather station.  Inside was jam-packed full of mainly dead cluster flies that could only have entered via an incompletely sealed cable access hole.

Conclusion? The roof room may its own openings, small or even quite large.

Sunny Sunday today and I decide to sit and do the crossword in the greenhouse warmth of the landing area of the roof room. Crossword completed and feeling smug but with thoughts of flies and apertures I decide to have a poke and a feel around the seams between huge glass windows, steelwork frames, and the flue through the ceiling above the solid fuels stove.  Et voila:

et

Two of the more obvious (and inelegant) holes through which desperate flies on a mission could enter.  Both big enough for a finger, let alone a fly could gain access.  Not only that, a heck of an inwards gale was howling!  A curious fly would get SUCKED in whether it liked it or not.

Operation seal-it-up commences forthwith