Over the winter and as we come into spring I have been attending a steady stream of call outs for rat infestations. Now this is not out of the ordinary and I would expect the odd call plus a few extra during times of snow (pushing rats indoors) or in heavy rain. What has struck me this year is the number of call outs that can be linked to sewer infestations. Rats, namely the brown rat have always been at home in sewers, indeed the brown rat is often referred to as the sewer rat, while its cousin the black rat is rarely found below ground. The sewers offer a protected underground habitat that allows rats to live and breed in perfect safety. Food is supplied on tap in the form both of human food stuffs flushed down the drain, including fat and grease and also in the form of human excrement, which they will feed on quite happily. Sewers are also cool in summer and warm in winter so infact offer a rather perfect enviroment.
When these small local populations reach a certain level then rats often make an appearance on the surface. This might be in the form of a new colony of younger rats or the customer might report a very large scaly, almost senile, rat wandering around in the day time. These are often old rats being driven out of the colony by the younger bucks. In a way these sewer populations act as a reservoir of rats that occasionally create new populations above ground.
Rats can also cause damage to sewers and drains through their burrowing in the soil around the joints, they can also increase the damage around deteriorating bricks in sewers. When rats are busy building nests or excavating their burrows they can fill the drains with soils and detritus, blocking drains and even causing drain collapse in the worst cases.
Councils and local authorities should undertake sewer baiting at regular intervals. This often takes, or in some places took, the form of baiting every man hole in each area on an annual or bi-annual basis, after a week or so these would be checked and those that had some signs of rat activity should then be baited with poison on at least two more occasions. Unfortunately due to council cutbacks in some areas this isn’t happening. Though this depends on the area and the authority in charge, some councils continue to do a good job.
In the photo is an example of the ledges or ‘benching’ that is found inside a manhole. Here I have baited with both grain bait and a soft pasta based sewer bait.