Section E
For more information on water beetle groups there is a freely available out of print FSC handbook available HERE
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Alternatively there are Mikes insect key with pictures, however you will need to know the family of beetles that it belongs to first
The Below beetles all have a streamlined oval form and tapered hind legs with stiff swimming hairs
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Dytiscus sp.
22.0-32.0 mm
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Long filliform (thread like) antenna
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racing green coloured body with lighter yellow markings
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Elytra may have deep ridges in females, or lightly punctured in males
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February - December
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ID Features
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Large ovate beetles with lighter bands on the pronotal margins.
There are 6 similar species in the UK.
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I recommend using
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Taking Photos
Dytiscus species require a photo of the underside with a clear focus on the hind coxal processes as the shape and colour is important for species-level identification. In addition, a good dorsal photo that has the front and hind margins of the pronotum, as the relative thickness of the bands can also be a good ID characteristic. This is good practice for all water beetles if you are not sure!
Dytiscus circumflexus​
An ideal underside photo showing the yellow underside colour and hind coxal process shape (Right)
indicative of Dytiscus circumflexus. Credit Gary Lowe
Dytiscus circumcinctus​
Dytiscus circumcinctus​ Credit Mike Southall
Dytiscus marginalis​
Colymbetes fuscus
ID Features
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15.0 - 17.0 mm
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head black with lighter labrum and markings above eyes​
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dark transverse reticulation on a light brown/olive coloured elytra
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legs orangy brown
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All year round
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Widespread
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Transverse reticulation on the elytra is a key ID characteristic for this species and can be viewed easilly using a 10x hand lens
Transverse reticulation. Bill Unwin 2017
Ilybius fuliginosus
ID Features
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10.0-11.5 mm
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Narrow oval body
Pronotum and Elytra with two very well marked pale stripes (pictured)
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Bronzy head with a paler front (Labrum)
Antennaepalpes pale brown/orange
Front legs usually paler than the mid and hind legs
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Jan - Nov
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Widespread
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Superficially, this looks similar to the much rarer, larger, and heavier set Cybister lateralimarginalis, Which has only been found 4 times in Britain, although found more frequently in continental Europe
Hydrophilus piceus
The Great Silver Diving Beetle is one of our largest beetle species in the UK.
Instantly recognisable from the other oval-shaped diving beetles due to their short, distinctly clubbed antennae, elongate shape, and size.
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34.0-48.0 mm
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Massive scutellum
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Body Black upper side with green/purple luster
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Short clubbed antennae
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long red maxillary palpi (twice as long as antennae)
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red antennae and maxillary palps
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February- December
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Local in SW & E England & S Wales
ID Features
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