Frequently asked questions on mosquitoes and other biting insects

(Produced by Michael Clarkson and Gail Chapman, Leahurst, University of Liverpool)

Have I been bitten by a mosquito?

A number of different biting insects may be a nuisance in the Neston area. These include mosquitoes, midges, horseflies and fleas. Midges are tiny flies with short biting mouthparts whereas horseflies are large with mottled wings and inflict a painful bite. Both horseflies and midges breed in mud on the Dee marsh and elsewhere. Dog and cat fleas bite humans and breed in pets’ beds and crevices around the house. Bird fleas and other fleas which normally occur on wild animals bite humans more often than you may think. Although mosquitoes are the most common nuisance biting fly, they are not always to blame!

What is being done about the mosquito problem in Neston?

In recent years Neston mosquitoes have been studied by researchers from the University of Liverpool (UoL) and Liverpool John Moores University, supported by Ellesmere Port and Neston Borough Council, Cheshire West and Chester Council and Neston Town Council (NTC). NTC has an active ‘Marsh Group’ with representatives of NTC, CW&C, the RSPB and UoL who meet regularly to co-ordinate research and discuss control of the marsh mosquitoes. In 2016, monitoring of adult mosquitoes is ongoing in the Neston area and of immature stages in pools on the marsh near Quayside. Weekly forecasts on the NTC website are derived from this monitoring.

More information on mosquito research in the area can be found in this document: Mosquito Group Research

Why does Neston have such a problem with mosquitoes?

There are over 30 different species of mosquito in Britain! At least 14 have been found in the Neston area. They look and sound the same but most can be identified under the microscope. One common mosquito only bites birds and never humans.  Most other species will bite humans though they usually prefer other animals. Only female mosquitoes bite as blood is needed to produce eggs. Males feed on fruit or flower juices!

Each species of mosquito has its favourite place to breed which can be in ponds or pools, flooded fields, water butts, tyres, buckets or other containers, and some only breed in tree-holes. A few breed only in salt water, usually sea-water, though they have been found in salt mines in Cheshire. In the Neston area, the breeding site for saltwater species is in pools on the Dee Estuary. These cover a huge area and allow for large numbers of mosquitoes to develop. The most important species biting people in the Neston area is the marsh mosquito, Ochlerotatus detritus.  There are at least 2 other species which can breed in salt water here.

Are there any health risks associated with Neston mosquitoes?

Although mosquitoes are important in the transmission of many diseases throughout the world, there are no human mosquito-borne diseases in the UK. There are a number of mosquito-borne diseases which cause outbreaks in Europe. If these diseases were ever imported they could potentially be transmitted by UK mosquitoes. Public Health England and others are therefore monitoring mosquito populations and carrying out surveillance for disease introduction.

The only current health risk in the UK from mosquitoes is from the itchy and often painful reactions to mosquito bites.

How do we know when the mosquito biting will be at its worst?

The marsh mosquito lays its eggs on the soil virtually anywhere on the marsh where they remain alive for as long as a year. A tiny larva develops in the egg which doesn’t hatch until the egg is submerged in water, which means either a high tide or heavy rainfall. It may take 6 or 7 immersions for all the eggs to hatch. The larvae feed on bacteria and other tiny particles and grow rapidly, shedding their skin three times so that the fourth stage larva is about 1 cm long. This changes into a comma-shaped pupa from which the adult emerges. All the larvae and the pupae need to be submerged in shallow water where they are very active but if the water dries out, they all die. If the weather is warm, development from egg hatching to adult mosquito may take just over 2 weeks. Eggs and larvae can live over the winter months but we have never found pupae later than September so no new adults emerge until the temperature rises in March or April and numbers fall from September.

In general mosquito numbers increase through summer as successive broods develop but in the case of the marsh mosquito this is complicated by the need for several immersions in water before eggs hatch. We have studied the immature stages on the marsh for several years and now have some understanding of the relationship between high tides, rainfall and mosquito development. This forms the basis of the forecasting system.

If these mosquitoes come from the marsh, how far do they travel?

Many species of mosquito only fly a short distance from their breeding sites but the marsh mosquito can fly or be blown a long way. We have found marsh mosquitoes from the Dee Estuary in Willaston, Thornton Hough, Heswall, Bromborough and Bebington as well as throughout west Wirral, a furthest distance of 8 km. When large numbers emerge on the marsh, they can bite people over much of the Wirral. Different species bite at different times of year but the marsh mosquito has the longest biting season of all British mosquitoes and can be found biting in any month.

Why aren’t the marsh mosquitoes controlled more effectively?

Although we have learnt much about the marsh mosquito and the factors giving rise to large numbers in the Neston area, we don’t know how best to control them. The Dee Estuary is a UK Site of Special Scientific Interest (SSSI) and a European Special Area of Conservation with unique flora and fauna, including huge populations of many bird species. Strict laws apply to the use of chemicals and altering the marsh habitat and use of any method must be approved by Natural England.

The only spray allowed is a biological method using bacteria which kill mosquito larvae (but not eggs or pupae) called Bti. This has been used on the Dee marsh for many years since 1983. It has temporary value but it is impossible and dangerous to spray all the pools so has been discontinued.

What is being done to try to improve the situation?

Scientists at LJMU are studying another biological control method using tiny worms which kill only mosquito larvae.

Since the immature stages require shallow pools with little flow, attempts have been made to alter the drainage so that the tides wash out the pools more often.

The Donkey Flash at Parkgate and the extension of pools near Quayside at Little Neston were designed to improve drainage. Monitoring of these pools has shown that these methods are successful – immature stages have never been found in these deep pools. However, getting rid of shallow pools on the huge area of marsh would be impossible unless the marsh was transformed into an enormous lake, so this method is of limited value. We have evidence that the increased drainage at Parkgate is more successful than at Little Neston which may be due to the fact that tides are higher nearer to the estuary mouth and so wash the pools out more efficiently.

What can I do to protect myself from mosquito bites?

Insecticide sprays kill adults and can be used in houses and on flying and resting adults in areas where barbecues are to be held. Always read the label and product information before use.

Other methods of control in gardens are the use of spirals, sprays and wrist bands which repel mosquitoes. These products contain DEET, of a concentration of at least 50% or citriodol and give protection for several hours. Those who prefer natural products may like to try creams containing Citronella and Aloe Vera. Always read the label and product information before use.

These products are available in chemists in the Neston area and can also be purchased online.

How can I make a mosquito trap?

There are many examples of home-made mosquito traps on YouTube, most of which are American in origin. One example which we have tried out is https://www.youtube.com/watch?v=qn1Uu00Ax5g

Residents may like to put them in their gardens when the forecast is red though we doubt if they will reduce the number of mosquitoes sufficiently to make a great difference! We intend to try some this summer and if you join us, please let us know the results via the NTC website.

Take care with sharp instruments when cutting the bottle. A suitable recipe for the attractant is 50 g brown sugar dissolved in 200 ml hot water. Allow to cool and sprinkle a few grams (teaspoonful) of dry yeast on the surface without mixing. Change the fluid every 2 weeks.

Please note that Neston Town Council does not endorse this YouTube video.  Other similar videos are available online.  If viewers choose to follow the advice in this video, they do so at their own risk.