Chironomids

We occasionally receive queries from residents about the presence of small, winged insects on their properties, some of which may swarm in large numbers. In spring, rainfall combined with a rise in temperatures allow insects such as mosquitoes, midges and chironomids to thrive. Many of these insects occur naturally near water bodies such as lakes and reservoirs. It can be very difficult to tell these insects apart.

Chironomids

Chironomids are mosquito-like insects that vary in size depending on the type of species.  The adult stage lasts for only a week during which time they swarm as part of the mating process. There are many different species that emerge at different times of the year, from March to October.

Chironomids occur naturally near all areas of open water. Chironomids and their aquatic larvae live in the mud at the bottom of water and are an important part of the food chain for other insects and birds including ducks.

Although the swarming of these insects, sometimes in considerable density, can be a nuisance, they are not hazardous to health. They have no mouth parts and are unable to bite. They do not spread disease.

Many of the queries we receive turn out to be chironomids

Midges

Midges is a term used to describe many different species of tiny flies. Not all species bite, but some do, and these bites can be quite painful. In the UK, there are more than 500 species of non-biting midges and more than 150 species of biting midges

Although biting midges may be a nuisance to us, many midge species are important food sources for other animals like fish, frogs, birds, and spiders. Midges do not spread infectious disease and are considered to be of a low public health significance.

Mosquitoes

The UK is home to more than 30 types of native mosquito species, some of which can bite.

The UKHSA monitor mosquitoes within the UK and more information on their work can be found here - Mosquitoes: surveillance and recording - GOV.UK (www.gov.uk). Members of the public can submit mosquitoes or photographs of mosquitoes to the UKHSA for identification.

We work with our colleagues in the UKHSA to detect non-native species of mosquitoes within the borough and more information on the national contingency plan for invasive mosquitoes can be found here - National contingency plan for invasive mosquitoes - GOV.UK (www.gov.uk). Invasive species of mosquitoes could spread disease and for this reason the UKHSA routinely monitor for signs of these species within the UK.

Can anything be done to eradicate them?

Chironomids and their larvae are an important part of the food chain for other insects and birds, and because it is illegal to apply any insecticide where there is a risk it could drift into other properties, Thames Water are no longer able to spray the reservoirs with insecticides.

Some reservoirs (including the Staines reservoirs) are sites of special scientific interest (SSSI's), which mean they are legally protected sites of national wildlife importance. Others (including the Staines reservoirs) are Special Protection Areas (SPA's), legally protected sites of European importance for their bird life. This means that Thames Water have a statutory duty not to adversely affect the wildlife interest of the reservoirs.

Because of these restrictions, Thames Water use environmentally friendly methods to help alleviate the issue, these measures include;

• using water sprays to discourage Chironomids from entering sensitive areas
• setting up brightly coloured markers in strategic locations which is hoped will attract the Chironomids away from sensitive zones, such as residential areas

If you believe insects are coming from a reservoir you can phone the 24-hour Thames Water Customer Centre on 0800 316 9800 or visit their website https://www.thameswater.co.uk/contact-us.

Thames Water has more information on their website about biodiversity and increased midges in the area around their reservoir. 

Biodiversity | Responsibility | About us | Thames Water

Removing any standing water in your garden can reduce the number of mosquitoes and midges in your garden.

• mosquitoes often breed in water butts. A well fitted lid will help to stop mosquitoes breeding in these containers
• blocked gutters and drains can provide habitats for mosquitoes, so keep them clear to allow the water to drain freely
• rain water can collect in litter, tarpaulins, buckets, open bins, wheelbarrows and tyres, so arrange these so that the water can drain away and remove any accumulations of waste
• water in paddling pools and bird baths should be drained and refilled every few days so that mosquito larvae do not develop
• encouraging more birds into your garden

You can reduce the risk of bites by wearing long trousers and long-sleeved shirts when mosquitoes and midges are active and by wearing suitable insect repellent.

In many circumstances we are very limited in the actions we can take. Local Authorities have some limited power to deal with nuisances caused by biting insects originating from commercial premises like food business or warehouses.

More information:

For more information, please contact the Environmental Health department on 01784 446291 or eh.residential@spelthorne.gov.uk.