They belong to the order Odonata, which means serrated teeth. If you are fast and silly enough to hold one, expect a nasty nip.
Damselflies are smaller but like dragonflies. They can be distinguished by
Dragonflies and their larvae are aquatic and eat just about anything—tadpoles, mosquitoes, fish, other insect larvae and even each other. Adult dragonflies are top predators in the insect world, and apart from being caught by the odd bird, live a full adult life (from a week to a year depending on species).
Dragonfly common names meant more when I learnt that they referred to hunting methods.
Hawking - Most dragonflies capture their prey in flight, plucking live insects out of the air. By forming a basket of sorts with its legs, a dragonfly can overtake a fly or bee and simply scoop it up and pop it into its mouth, without stopping. Some, like darners and spread wings, will just open their mouths and swallow whatever they catch as they fly. Dragonflies that use hawking to catch their prey include darners, emeralds, gliders, and saddlebags. Unfortunately some common names can be misleading. Common names for Pantala flavescens are wandering glider, globe wanderer and globe skimmer.
Dragonflies breed in the Claypit where I found a wandering glider that had just emerged there from its larval shell. It is amazing how a dragonfly can emerge from its much smaller larva. Wandering gliders can fly up to 4,000 kms to complete their life cycle.
Net-winged insects like lacewings can be confused with damselflies. They evolved about 50 million years later as land hunters that do not need water for breeding. A way to detect them is to look for their antennae, that dragonflies and damselflies do not have. They are most active in the evening.