Scarlet Darters (Crocothemis erythraea) reach a length of 33–44 mm and have a flattened and rather broad abdomen.
The adult male is easy to recognize; it has a bright scarlet red, widened abdomen, with small amber patches at the bases of the hindwings.
Also the head, face, eyes, legs and veins on the leading edges of the wings are red.
Females and immatures are yellow-brown and have a conspicuous pale stripe along the top of the thorax.

1st & 2nd photo: A male. Carrusqueira, Sado Estuary Nature Reserve, Portugal, 1 October 2021
3rd, 4th & 5th photo: A male. Parque da Cidade do Porto, Porto, Portugal, 6 June 2023