The insect order Odonata is an old insect order having evolved in the Pennsylvannian and dominated in the Permian. Today, there are about 5,000 species grouped into three extant suborders: Zygoptera - damselflies (Figure 1); Anisoptera - dragonflies (Figure 2); and Anisozygoptera, a small suborder of two Asian species morphologically intermediate to the former two groups. Two of the world's three suborders - Anisoptera and Zygoptera - are found in Michigan.
Distinguishing between the two suborders is rather easy, based on body shape and posterior abdominal features mentioned in the key below. Both the larvae and adults of all Odonata are carnivores. Larvae of almost all species are aquatic, respiring by means of gills (internal with Anisopera, external with Zygoptera, the later that may also cutaneously respire). The modified labium, used by all larval odonates to capture food, characterizes the larval stage of this order from from all other insects. It is held underneath the head, and, when prey is detected, thrusted out in a lightning-like strike. Prey is then seized with palpal lobes at the end of the labium, brought to the mouth and finally macerated with the larva's mandibles.
1a. Body slender, head wider than thorax and abdomen (Figure 1a1); abdomen terminating in three caudal lamellae (gills) (Figure 1a2 and 1a3) - Zygoptera
1a1Fig. 1a2 Fig. 1a3
Fig. 1a1: Enallagma ebrium larva, (6x, dorsal view).
Fig. 1a2: Ibid., (6x, lateral view).
Fig. 1a3: Ibid., (12.5x, dorsal view).
1b. Body stout, head usually narrower than thorax and abdomen (Figure 1b1); abdomen terminating in 5 short, stiff, pointed appendages (Figure 1b2) - Anisoptera
Fig. 1b1Fig. 1b2
Fig. 1b1: Cordulia shurtleffi larva, (3x, dorsal view).
Fig. 1b2: Erpetogomphus designatus larva, (6x, dorsal view). Dark spots on the epiproct are tubucles that normally develop on maturing male larvae, and are particularly evident on larvae of Gomphidae, Aeshnidae, Corduliidae and Macromiidae as well as some Libellulidae.