Richings Park and Thorney Residents Association

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Fly Infestation

The Richings Park area has experienced a problem with small flies with the source being the Iver Sludge Treatment Works located over the M4 down Old Slade Lane.  To date, Environmental Health Officers of both South Bucks District Council and Slough Borough Council have been monitoring the effects of the control efforts (chemical control) by Thames Water. To this end, they have asked if we could submit regular updates on infestations to assist them in this task.  The Residents Association have taken on the task of collecting and collating these fly activity reports.  If you wish to report an incident of flies at your home then please complete the attached ONLINE FORM.

Following on from a report submitted on July 9, 2012, we received the following statement from Thames Water

With regard to the operation of Iver South, we now do not store any sludge cake (which is the medium that the flies use to incubate their eggs) in the outside bays from the beginning of April to the end of October each year.

We have installed heavy duty industrial PVC partitioning around each of the storage bays to allow for a specialised form of treatment known as ultra low volume insecticide application.  This method gives us a very good kill rate, however, we have seen an increase in the rate of reproduction due to the increased temperature and humidity, which is generated by the sludge cake when the bays are enclosed.  This is being addressed by providing additional ventilation at the rear of the bays.

Currently, we are only able to use an adulticide to kill the adult stage of the flies.  We are once again investigating the use of a larvicide and various application techniques for the use of such a product.  These investigations are ongoing and will also include any environmental impact such a product may or may not have, as a matter of good practice.

Based on a visual inspection of all bays this morning, prior to treatment today, our view is that the fly numbers are substantially reduced.

We hope that this reassures you that we are doing everything possible to treat the flies in the most effective manner at Iver South, but if you have any questions, please do not hesitate to contact us.

We received the following email message on July 11th, 2012 from the environmental Health Officer for South Bucks

As you know, we (residents mainly) have had a very bad year concerning flies and I must admit that Thames Water, despite their efforts thus far, have struggled to cope with the deluge. The sludge cake at Iver South is stored in four bays with the ultimate intent to sell to farmers.

Demand for Sludge Cake is slow hence Thames Water is unable to shift the cake as quickly as they would prefer. Despite a distance of 500 metres approximately, the flies are still of concern to residents due mainly to the direction of wind flow and obviously humid condition. Following a recent meeting with Thames Water and Slough Borough Council, Thames Water confirmed and acknowledged that fly numbers were high and appeared keen to explore a variety of control options aimed at reducing numbers. So far to date, they have enabled the following:

Installed heavy duty tarpaulin type curtains for each cake storage bay

Increased the frequency of spraying of each bay

Increased the usage of insecticide (Aquapy) being used for each bay

Both a fan like mist dispenser to facilitate application of the chemical

Will improve ventilation and temperature levels within the bays to reduce breeding levels


To check and ensure that treatment efforts are working, we will need to undertake some fly monitoring at residential properties most affected in the above areas of Iver – The Poynings, The Ridings and Old Slade Lane.

We have now agreed a method of running this monitoring which will involve 6 houses, 2 in each road, and involves collecting flies on flypaper and submitting them for counting.

As a result of submitting a report in April 2012, we received the following reply from the consultants who are monitoring the situation:

Thames Water is in the process of screening the bays at Iver South SDC to enable better control of the flies on site. This is nearly complete and the treatment company has been able to conduct two sprayings. We expect further treatments very soon and hope that this will be reflected in a much improved situation for your residents.

As a result of submitting a report on July 11, 2011 the following responses were obtained from the consultant entymologist and the local environmental health officer.

Entymologist : Due to changed health and safety procedures at Thames Water, we had to revise the control and monitoring techniques. Unfortunately, this has taken us rather long this year. In addition, we had a sudden increase in temperature early in the year, which took as by surprise. We apologise if you have experienced higher numbers of flies. Thames Water has decided to install screens at the covered bays, so that these can be fully enclosed for a better treatment; this will happen over the next months. Furthermore, the bays were treated last week and today, they will be treated again this week Thursday. We hope this will reduce numbers of flies to a acceptable level. Thames Water is currently drafting a more detailed information release and will send this out to you and the Enviromental Health Departments next week.

Please note that the flies of concern at Iver South are Lycoriella ingenua, a species of Sciaridae. This fly is known to breed in compost and can often be found in pot plants. It also is known to cause a nuisance in mushroom farms. It does NOT transmit any diseases.

Environmental Health Officer: Just so you are aware, and in anticipation of situations like this, I designed a new fly nuisance leaflet to assist SBDC residents.  This leaflet could be accessed on our website at:

I will try and place a fly monitoring log sheet on the web page before the week runs out, which could be downloaded by residents. Additionally, complaints can be registered with the District Council through the normal process, with the response focused on monitoring number trends weekly over a 48hr period.  

The following update from South Bucks was received on August 14, 2015

Dear Resident,

I write to provide you with a summary on the fly nuisance investigation I have undertaken following receipt of further complaints at the end of July 2015. Following discussions with Entomologists working for Thames Water, a site visit to the Sludge Dewatering works confirmed fly activity being very low at the site. It became clear that “secondary breeding” sources local to the Richings Park area, were likely. To this end, commenced a detailed investigation involving: visits to residential properties to assess the level of infestation, visits to potential secondary breeding sources – golf course, ostrich farm, farms with animal husbandry and those for general arable farming.

This week, following a review of the spread of complaints from the Richings Park area, I felt it was necessary to return to the Old Slade Lane area on 12th August 2015, but this time, with a desire to inspect the fields/farm land close to the M4 motorway, which are in direct line of site of the sewage sludge works and adjoining arable fields on Old Slade Lane and those North of Richings Park towards the Railway Station.

My findings are outlined below:

(1)  I identified a significant stockpile of horse/cattle manure on fields close to the M4 boundary where potential fly breeding is likely. Subsequently, efforts are now in place to get the land owner to assist the occupier to remedy this concern.

(2)  I found lots of black flies at random on oilrape seed planted on fields adjacent to Old Slade Lane/The Poynings and similarly on fields to the North of Richings Park behind the Church. I made contact with the farmer who acknowledged the problem with the flies, but expressed insecticidal control constraints in place nationally. However, he has confirmed he will be harvesting both fields (Old Slade Lane and land abutting Bathurst Walk) in the next few days.  

At this stage, and in the absence of independent entomological verification, it is possible that both locations above, on a balance of probability, are secondary breeding sources for these flies.  This is in addition to potential secondary breeding sources which may exist at residential properties. These flies – Fungus Gnats, are known to lay their eggs in various forms of compost housing weak or dying garden/house plants. The larvae attack the roots of weak plants.  Adults do not bite but generally are a nuisance in large numbers. It is recommended for all such plants in your home or garden, be removed and destroyed. Compost bins must be dry and regularly turned to avoid breeding.

I would seize this opportunity to thank those who have assisted with providing fly strips as these have been useful in showing the extent of infestation at individual properties. In addition to this, I would be happy to collect dead specimens in jars/containers. If you are able to assist, please proceed to prepare an empty jar (i.e. jamJam jar), line the bottom with clean tissue then place samples/specimens in the jar. Please remember to label the jar with your name, address, email, mob number etc. and contact Environmental Health ( or 01895837264) to arrange collection.

Finally, I trust this update is of assistance

Update from South Bucks Environmental Health Officer ( Adrian Dillon ) on April 15th, 2016

A meeting was held with representatives of Thames Water, Slough Borough Council, and the Environment Agency about a week ago.  It was reported that the screens to the cake bays had suffered storm damage over the winter and TW were waiting on delivery of new screens expected to arrive on or around April 25th.  In the meantime, the absence of screens was preventing them from spraying the cake bays with insecticide as this would simply escape into the air.  The fly breeding season would also appear to have started earlier this year.  A new protocol was going to be adopted this year with regard to spraying which should make it more proactive rather than being simply reactive whenever problems started being reported.

Email from Thames Water on April 20th, 2016

Thank you for sending through the log of fly complaints, I am very sorry to hear that you and other residents are finding themselves in this distressing situation. (I hope the following information brings you some confidence).

As you may be aware, the curtains that are located around the perimeter of the bays that allow the cake to be treated were damaged in the strong winds in February.  I can now confirm that the refurbishment to the curtains will commence on 25 April 2016, however, we are aware of the negative impacts that the increase in flies has on residents and local business owners alike.  Therefore Richard Dennett (Operations Manager) has commissioned a temporary repair of the curtains that took place on 18 April 2016 (at an additional cost of £6000).  This temporary measure will allow for treatment to take place as early as 21 April. 

Going forward, we will be conducting asset condition surveys, this will mean we will become much more apt at troubleshooting and dealing with the flies before they become a problem to you and your fellow business neighbours.

Please do not hesitate to get in touch should you require further assistance.