Dragonflies benefit from cleaner water

14/07/2009 15:00

The dragonfly population has thrived in the Netherlands in recent years. The variety of species has grown or at least remained stable. Species usually found in brooks and pools are doing well, but other dragonfly species have been reduced.

All dragonfly populations in the Netherlands

All dragonfly populations in the Netherlands

Cleaner water

One of the reasons for the dragonfly population increase in the Netherlands is improvement of the water quality in brooks and pools.  Due to improvement of the water quality, the diversity of water(side) plants, which has a positive effect on most dragonfly species, has become richer. Climate change may also partly account for the increase in the number of dragonfly species.

Dragonfly species in brooks, pools, peat bog wetlands and dune water areas

Dragonfly species in brooks, pools, peat bog wetlands and dune water areas

Species typically found near brooks and streams, e.g. the Beautiful Demoiselle, the Banded Demoiselle and the White-Legged Damselfly thrive in cleaner water. A number of species typically found in pools is growing fast, e.g. the Small Red Damselfly, the Small Spreadwing and the Downy Emerald. Apart from water quality improvement, a markedly lower acidification rate also plays a part in this respect.

Four dragonflies typical of acidified pools

Four dragonflies typical of acidified pools

Various species are diminishing in numbers. These are typically the four species mainly found in pools with a high acidification rate, e.g. the Black Darter, the Common Spreadwing, the Four-Spotted Chaser and the Common Blue Damselfly.

Risk of running dry

The number of dragonfly species common in peat bog wetlands has increased marginally in recent years. The water quality in peat bog wetlands, however, has not improved so fast as in pools, brooks and streams. To prevent peat bog wetlands from running dry, polluted water from other areas is often let in. Some species like the Scarce Chaser, the Yellow-Spotted Whiteface and the Green-Eyed Hawker are thriving. The Green Hawker, a species included in the Habitats Directive , is under threat of extinction.

In the coastal dunes, dragonflies are not doing well. More common species, such as the Migrant Hawker and the Common Spreadwing are declining dramatically. An important reason for their disappearance is that many small dune water reservoirs are at risk of running dry. If this process can be stopped, dragonfly numbers might increase in the years to come.

Lodewijk van Duuren (CBS) and Dick Groenendijk (De Vlinderstichting)