Floods and problems with pests


Floodwaters often bring mass devastation, flooding homes and other premises, causing stress and deprivation. The presence of floods also frequently heightens the risk of disease.

floods 3

Floods can create the perfect environment for pests, such as rodents, since they are often displaced from sewers and burrows. The standing water, waste, sewage and debris left behind provide ideal breeding grounds for insects such as mosquitoes and other flies. Such favourable conditions can result in an abundance of disease carrying and nuisance causing flies, posing a significant risk to health.


Coliform bacteria and other faecal organisms can be associated with floods, stormdrains, sewer back-up incidents, etc. Weil’s disease or Leptospirosis, carried by rodents, has been associated with flooding. Some studies have found a 15-fold risk of the disease associated with walking through floodwaters. A recent report revealed that there were 42 cases of Weil’s disease
reported in England in 2010. Epidemics may be associated with changes in human behaviour, animal or sewage contamination of water, changes in animal reservoir density or following natural disasters such as floods. It is important to be aware of the flu-like symptoms caused by a Leptospirosis infection. Those who may be exposed to Leptospirosis should take relevant precautions listed on the ‘Leptospirosis (Weil’s disease)’ cards, which should be kept with you at all times.



Filth and debris left by the floodwaters create excellent breeding conditions for houseflies, mosquitoes, other flies and insects associated with decaying organic matter. Those insects may be capable of causing significant nuisance and in some cases spreading disease.

Control of such insects involves removal of the breeding source, which can be standing/stagnant water, and accumulations of organic matter in drainage systems. Flooded cellars in particular, can harbour Culex pipiens biotype molestus, a human-biting mosquito. Accumulations of decaying organic matter can provide breeding sites for a number of different ‘drain’ flies that may be involved in disease transmission and can certainly reach nuisance proportions. Such families of flies include the lesser dung flies family Sphaeroceridae, fruit flies family Drosophilidae, owl-midges or bathroom flies family Pyschodidae, fungus gnats family Mycetophilidae, sciarid flies family Sciaridae, window gnats family Anisopodidae and others. Sites that are very wet, for at least part of the year, may favour the development of biting midges, family Ceratopogonidae.

Sewer rats, or brown rats, are sneaking into houses in the UK to escape the flooding
Sewer rats, or brown rats, are sneaking into houses in the UK to escape the flooding


After flooding, many rodents are displaced from their natural habitat. The rodents will then find areas that provide food, water and harbourage. Inevitably, rodents enter houses, sheds, barns, and other buildings. Flood-damaged premises are particularly attractive and provide easy access for rodents. These unwelcome rodents may cause damage to property directly by gnawing or indirectly by depositing faeces and urine. Rodents can threaten public health, as they may carry diseases such as E.coli, Salmonella and leptospirosis. The high instance of recent flooding in the UK has increased concern regarding exposure of householders to these diseases and rodent control is likely to become increasingly important.


The Environment Agency recommends the following Safety Precautions:

Wear protective clothes, sturdy boots and waterproof gloves and face masks when handling debris

• Floodwater may be contaminated by sewage, chemicals, or rat’s urine (leading to Weil’s disease)

• Keep your hands away from your face while cleaning and always wash your hands if you come into direct contact with floodwater or silt

• Wash all cuts and grazes and cover with a waterproof plaster. Get a tetanus jab if you are not already inoculated

Contact the Environment Agency for further advice on cleaning up after a flood: 0845 988 1188.

Thanks to Killgerm Chemicals for the information.

Best Pest Control

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