Morphology of the Nymphs

Odonata nymphs are distinguished from other aquatic insects by the presence of an enlarged, extendable, labium that is longer than the head. Nymphs of Zygoptera and Anisoptera suborders can be distinguished from each other because those of the former are slender, the head is wider than the thorax and abdomen, and the abdomen has three caudal gills. Anisoptera nymphs are stouter, the head is usually narrower than the thorax and abdomen, and the abdomen has five caudal appendages. An understanding of the morphology of Odonata nymphs is important to enable confident use of the keys. Detailed illustrations of the Anisoptera nymph body are provided in order to facilitate the identification of suborders, families, and genera. The head and abdomen possess the most important characters for identification. The most taxonomically informative characters are as follows: in the head, the antennae and mouthparts, and especially the prementum; in the thorax, the pronotum and legs; in the abdomen, its shape, the presence/absence of dorsal and lateral spines, and the shape and length of the caudal appendages. Photographs of the dorsal, ventral, and lateral aspects are included.