Drain Fly/Larva Infestation

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  #1  
Old 12-04-18, 11:48 AM
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Drain Fly/Larva Infestation

So, we have been occasionally getting drain flies in the house. I thought nothing of it, and on an unrelated note, our septic system backed up and needed repair. As he was covering things up, he wanted to make sure our grease trap (which is hooked up to our kitchen sink and dishwasher) was working.

As I began to run the sink and dishwasher, nothing was coming in. He opened the crawlspace and said there was a leaky pipe. He was licensed to work on the outside of the house, but not on the inside.

That all being said, I said I could handle a leak and repair it myself. I threw on my headlamp and went under....

Oh. My. God.

To call it an infestation I feel is a bit of an understatement. Larva were crawling on top of each other in segregated puddles a good 1/4" thick. Swarms of flies and feasting spiders everywhere.

The pipe didn't have a crack, it had severed completely and had been pouring under our house for who knows how long.

How do you kill flies and larva on this kind of scale? Pipe repair is the last thing on my mind.
 
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  #2  
Old 12-04-18, 04:04 PM
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Larva were crawling on top of each other in segregated puddles a good 1/4" thick. Swarms of flies and feasting spiders everywhere.

I could be wrong here but I think diatomaceous earth would knock them down in a hurry?

Diatomaceous earth is a sedimentary rock with a wide range of cleaning and insecticide applications. Sprinkle enough diatomaceous earth over the maggots to completely cover them. It will stick to their exoskeletons, dehydrate them, and kill them from water pressure deficiency.

Few years ago I bought a big bag of floor dry at CarQuest and much later I noticed it said "diatomaceous earth", I had no idea what that was. If I remember correctly a 25# bag was just a few bucks.

Might help

Good luck under there.
 
  #3  
Old 12-04-18, 05:23 PM
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Drying out the crawl space will stop the life cycles and you're going to have to do that mechanically with fans or forced air or dehumidifier even after the leak is fixed. For a temporary fix immediately prior to going under to fix the pipe(s) you could try a space spray such as an aerosol type yard fogger as you can direct that spray around the crawl space as opposed to total release aerosols that simply spray up and a little bit around and fall back down. Find a yard fogger that is for flying insects such as flies, mosquitoes, gnats, etc.

If you can work among the larvae/adults then consider that as getting the pipe fixed is paramount here. You could fog the crawl space later or you could do it before and after.

After application, it will need several hours of settling time before you can enter for repairs.

How wet is it in there? Is it a dirt floor crawl? Is there water pooled up?
 
  #4  
Old 12-04-18, 05:59 PM
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Ugh, repair isn't going well.

I drug a garbage bag down and scooped up most of the larva with a garden shovel and dumped it in the bag, but there's still a lot. It's dirt floor, with a mediocre attempt at covering it with 5 mil, a patchy job at best.

In an attempt to fix the pipe, I managed to not fix the busted pipe, cut my finger open, and crack a joint further down the line. After that fiasco, I called it quits for my own sanity. I don't know who repaired this last time, but just standard tape isn't going to cut it folks, and the PVC repair is shotty at best. And don't get me started on them using bricks to prop up the pipes. I'm beyond pissed at the previous owners. End rant.

The kitchen sink is off limits since the leak has been found. Essentially, this will be the end for moisture down there (save the bits that leak out during repairs.)

I'll probably make another attempt tomorrow.
 
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Old 12-07-18, 04:15 PM
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Repair complete, there were two massive clogs, one of them about 3 feet long and about 80% blockage, the other about 1 foot and 100% blockage. I think that is what was responsible for the busted pipe.

Anyway, cutting the water back and fixing the pipe has brought down the infestation down drastically.

After things dry out, should I maybe just fog out the crawl space?
 
  #6  
Old 12-08-18, 06:22 AM
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Good job on the troubleshooting and the repairs!

With flies, especially the smaller species of flies, once their harborage/breeding sites are destroyed there is usually nothing else to do.

Did you remove much of the decaying organic matter? It seems that you did, according to an earlier post. Removing that to a large extent and drying out the area are necessary for control. If the area doesn't dry out, then the life cycle will slow down but not stop. Insecticides treatments will kill the adults but eggs/larvae/pupae will continue to the adult stage. I've performed insecticide treatments for these flies, but that was to make it more bearable for the workers. In other words, a temporary fix so they could work.

Consider using mechanical means such as fans or dehumidifier or fresh air ventilation for expediency.
 
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