The shape of the hind margin of the pronotum is diagnostic in blue damselflies. The illustrations below are of male insects however the shape is similar in both sexes.
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| Common Blue Damselfly Enallagma cyathigerum The hind margin has a flat, shallow central lobe | Azure Damselfly Coenagrion puella The hind margin is broad and flattened |
Variable Damselfly Coenagrion pulchellum The hind margin has a prominent, narrow central lobe |
Irish Damselfly Coenagrion lunulatum The hind margin has a distinct raised lobe |
| Nelson, B., Thompson, R. & Morrow, C., 2000 (August 28). [In] DragonflyIreland http://www.ulstermuseum.org.uk/dragonflyireland/ |
| Copyright © National Museums and Galleries of Northern Ireland and Environment and Heritage Service, 2000 |