Dorset’s Aquatic Invertebrates

Aquatic Invertebrates

For aquatic invertebrates, Dorset’s diverse geology and topography has provided all the major habitats types from bogs, flushes, winterbournes, streams and ponds up to all but the largest rivers and lakes found in the country.

This diversity offers homes to a great variety of aquatic animals and plants from the commonplace to the extremely rare. We are also lucky to have a number of local experts as well as visitors to the FBA River Laboratory who have over the years compiled an extensive list of species. As always, there is more to discover and you can easily contribute through the Riverfly Partnership that helps monitor the health of our streams and rivers or through pond dipping in your local pond and recording what you find.

Aquatic invertebrates come in all shapes and sizes with the major groups listed on this page.

Crustacea

Crustacea are common in all but the most acidic waters – Water Hog Louse and Freshwater Shrimp being the commonest with subterranean shrimps sometimes washed out at spring heads and Fairy Shrimp in seasonal ponds being the rarest. There are also many microscopic Crustacea such as water fleas, some of which can be identified via the online guide at the Cladocera Interest Group.

Leeches

Medicinal leech

Medicinal leech

Photo: Rob Aquilina

Leeches also range from common species found in all streams and ponds to the Medicinal Leech, which is our rarest native leech, still found in some Dorset ponds.

Stoneflies

Adult Stonefly from the Nemoura family

Adult Stonefly from the Nemoura family

Photo: Rob Aquilina

Stoneflies are found in running water as they require high oxygen levels. One of the rarest species in the country has only recently been found in Dorset.

Mayflies

Mayfly nymph

Mayfly nymph

Photo: Rob Aquilina

Mayflies are found in both still and running waters but are much more diverse in rivers and streams. Often turning up in moth traps, the adults can be difficult to identify as they often need microscopic examination.

Caddis flies

Philopotamus montanus

Philopotamus montanus

Photo: Rob Aquilina

Caddis flies are famous for their intricate cases but there are a number of families that are free-living in streams. The adults also turn up in moth traps.

Dragonflies and damselflies

Dragonflies and damselflies are the iconic aquatic insects. Easily identified with close-focussing binoculars and field guide without the need to catch them. See the Dorset Dragonfly Group website

Water bugs

Water bugs are the most specialised of the aquatic insects in terms of their body plans which are very diverse. Many are immediately recognisable just by their shape. Others need more careful examination.

Water beetles

Diving beetles: Acilius sulcatus, Asulcatus

Diving beetles: Acilius sulcatus, Asulcatus

Photo: Rob Aquilina

Water beetles are also very well adapted to the water, especially diving beetles (Dytiscidae), water beetles (Hydrophilidae) and whirligigs (Gyrinidae). Other families seem out of place but certainly thrive in their chosen habitats including riffle beetles (Elmidae), burrowing beetles (Heteroceridae) and some specialised aquatic weevils.

Freshwater snails

Sphaerium

Sphaerium

Photo: Rob Aquilina

Freshwater snails are familiar animals (Ramshorns and Pond snails being the two major families) but there are also a variety of freshwater bivalves ranging in size from a few millimeters (Pea and Orb mussels) up to the 20 cms Swan mussel found in lakes and rivers.

Further Information

Help with identification can be found on websites such as iSpot, or Buglife’s Bug identifier.

I am always happy to try to identify photos sent to me (via www.aquilina-environmental.co.uk where you can also download a list of identification guides).

Records can be submitted via Living Record (look for Freshwater Subjects on the Options page) or in a spreadsheet sent directly to DERC

Rob Aquilina