Threats To Dragonflies

Britain’s climate is becoming warmer and extreme weather events are becoming more frequent (Met Office, 2025). The impacts of climate change on dragonflies are complex. Some species appear to benefit from the warmer conditions; for example, the Emperor Dragonfly (Anax imperator) has expanded its range north in recent decades. Other species appear to be negatively affected.

 

Sea level rise

The sea level around the UK has risen, on average, by about 12–16cm since 1900 (Horsburgh et al., 2020). More frequent storm surges also increase the risk of coastal flooding. Lowland areas in the south of England are most affected; as a result, species with populations in coastal wetlands within the south of England are most at risk. This includes the rare Dainty Damselfly (Coenagrion scitulum), which is currently limited to a few sites in the coastal marshes of Kent.

 

Warmer summers and winters

Different species have adapted their behaviour and physiology in order to maximise survival and breeding success in different climates.

The Broad-bodied Chaser (Libellula depressa) is widespread across southern and central Europe and its range is expanding north, most likely in response to climate change. The males have a waxy, ultra-violet-reflective pruinescence covering their abdomen, which reduces heating and water loss (Sformo and Doak, 2006). This adaptation allows them to stay active longer in warmer conditions, defending territory and attracting females.

The Black Darter (Sympetrum danae), on the other hand, has a more northerly distribution in Europe and has exhibited a long-term decline in England. With its dark colouration, this species can be active at lower temperatures but has poor thermoregulation which means warmer summer temperatures may limit the species’ breeding and foraging activity (Moore et al., 2024).

Increasing temperatures can also affect habitat quality and availability. For example, higher water temperatures lead to a lower oxygen availability, which can negatively affect larvae survival. Temperature also affects vegetation growth and structure; warmer temperatures accelerate vegetation growth, which can result in small, shallow, waterbodies becoming rapidly overgrown.

 

Extreme weather events

Storms, including periods of heavy rainfall, are becoming more frequent in the UK. As the large amount of water, produced by these downpours, flows over the land, before entering waterways, it picks up sediment, nutrients and pollutants. Heavy rainfall can also overwhelm sewage systems leading to spills of raw sewage into rivers. The fast flow of water, and the debris it carries, also act as a physical threat to larvae within rivers and streams.

Droughts are also becoming more frequent. Long periods of no rainfall can result in the desiccation of waterbodies, killing the aquatic larvae that live there, and reducing the availability of breeding habitat. Droughts can also have more long-term impacts on waterbodies; when waterbodies refill, following a drought, their vegetation structure may have been altered. Sphagnum bog mosses, for example, are aquatic plants, within which some dragonfly species, like White-faced Darter (Leucorrhinia dubia), lay their eggs and their larvae live. These plants die as they become desiccated and can be eradicated from bog pools during drought, reducing the suitability of these waterbodies for breeding dragonflies.

Plastic

Due to the large quantity of plastic in our modern environment, it is now also prevalent in our wetlands. This is because plastic does not degrade; instead, larger plastics break down smaller and smaller until they are microplastics. Ingestion/absorption of microplastics is harmful to our health (Li et al., 2023) and the health of our wildlife, including dragonflies. Dragonfly larvae can confuse microplastics as prey and eat them by accident; they can also ingest zooplankton and smaller macro-invertebrates, which contain microplastics. Bioaccumulation of microplastics in dragonfly larvae has been documented (Maneechan, 2022), a condition that causes neurotoxicity (harm to the larva’s nervous system) and increases oxidative stress, which can result in cell and tissue damage (Guimarães et al., 2021).

 

Nutrients – fertilizer, livestock waste, and sewage

Nutrients are important, as they support aquatic plants and algae growth; however, when nutrient levels become too high the ecosystems can become unbalanced. Excess nutrients encourage rapid plant and algae growth, which can result in wetlands becoming overgrown and experiencing ‘algal blooms’. In addition, the decomposition of the excess plant and algae material uses up large amounts of oxygen, reducing oxygen availability for dragonfly larvae and other aquatic wildlife. In some cases, the oxygen is too low to support life creating ‘dead zones’.

Sewers take sewage to treatment works where water is treated before being returned to rivers and the sea. However, during periods of heavy rainfall sewage systems can be at risk of becoming overwhelmed. When this happens, water companies discharge untreated wastewater, including sewage, directly into waterways; these events are called storm overflow releases. Along with other pollutants, sewage contains high levels of nutrients: phosphorous and organic material that breaks down into ammonia.

Farmland is a significant source of excess nutrients (nitrogen and phosphorous) input into UK wetlands. This includes fertilizer applied to crops, slurry or poorly stored animal waste, and soil sediment.

Drainage

Wetland drainage has been taking place in the UK for thousands of years but accelerated during the agricultural and industrial revolution. Drainage takes place for various reasons, but it is usually to make land suitable for urban development, forestry or farming. As a result, we have lost vast areas of wetland habitat, from lowland marshes to upland blanket bog. For example, Medieval Lincolnshire was covered in extensive areas of ecologically rich marshland which was subsequently drained to create the agricultural landscape we known today.

 

Waterway engineering

All lowland UK rivers have been altered in some way; many have had sections straightened or dredged in sections to reduce flooding in the immediate vicinity and allow floodplains to be used for agriculture and urban development. This homogenisation of river-ways reduces the variety of ‘niches’ available. For example, the straightening of a meandering river removes the areas of slower flow, which exist on the outer bends, where aquatic plants will be more abundant; this an area that is likely to attract breeding dragonflies, such as White-legged Damselflies (Platycnemis pennipes) which lay their eggs on the underside of the leaves of floating plants.

Intensive dredging of river and other waterbodies, such as ponds and lakes, can directly remove larvae in the process but also reduces their suitability for dragonflies to breed in the future. For example, the dredging of grazing ditches results in the removal of vegetation used by species such as Norfolk Hawker (Aeshna isoceles) for egg-laying and emergence.

Intensive bankside works can result in large quantities of soil sediment entering a water body, adding nutrients, which can result in eutrophication.

 

Water abstraction

As the UK population grows so does our daily water consumption, with the average person in England using 140 litres per day. Water is sourced from rivers, lakes, reservoirs, estuaries and groundwater. Reduced water level and flow in our freshwater wetlands can reduce their suitability as breeding habitats for dragonflies. In 2016, unsustainable abstraction prevented as many as 15% of river waterbodies from meeting good ecological status* or potential.

 

*Ecological status is assigned using biological and physico-chemical test results as well as assessments of the degree to which humans have modified the structure of a water body.

 

Disturbance

Wetlands provide us with a wide variety of services, including recreation; for example, since the pandemic, wild swimming has seen a surge in popularity.

While spending time outdoors in nature is important, heavy recreational use of a wetland can reduce the habitat quality for dragonflies and can disturb or kill the dragonflies that live there. Public use of protected sites that support threatened species is particularly concerning. For example, Moat Pond in Thursley Common SSSI supports a population of Brilliant Emeralds (Somatochlora metallic); however it is regularly used by swimmers, boaters and dog walkers; these activities churn up the benthic layer of leaf litter where the larvae live, disturb breeding adults and introduce pollutants, such as flea treatment pesticides and sunscreen.