Odonata are fierce predators of other insects. They are successful hunters, relying on speed, agility, and stealth: they are apex predators of the insect world.
Because they occupy separate and dissimilar environments, there is no competition between larva and adult for food or space, and larvae are safe from predation by the adult. This is a successful strategy and increases the likelihood of a sustainable population.
Odonata nymphs live in the sediments at the bottom of ponds, lakes, and rivers, and eat other water dwellers.
Nymphs are aggressive hunters, and will eat almost anything that is smaller than themselves that they can overcome. Typical food sources are other aquatic insects and larvae: mosquitos, worms, beetles, tadpoles and small fish may all be taken. Larger dragonfly larvae may tackle prey as large as a Stickleback. Nymphs aren’t fussy eaters, and they may be cannibalistic and eat other Odonata nymphs too.
Most are ambush hunters; they rely on cryptic or camouflage colouring to remain undetected as their prey passes unawares. Keeping very still and using their antennae and fine sensory hairs (Setae) that cover their body to detect their victim, they capture it using their labium.
Other species though are more active stalkers and use a combination of stealth and speed to overcome their victims.
Either strategy may utilise visual or tactile methods of finding their food. Species that inhabit clear running water favour visual strategies, and in murky waters the bottom dwelling species rely more on tactile strategies, sensing prey by using their antennae and the fine hair-like structures that cover their body.
Once their victim is selected, the nymph uses a specialised adaptation of their mouthparts called the Labium, or mask, to capture their prey. The labium of dragonflies and damselflies is a distinctive feature and is used in a way that is unique to Odonata.
The labium is long and terminated with two pincers; at rest it is folded it beneath the head and thorax. In this position, the labium may cover the front of the head giving it the appearance of a mask, hence its common name.
The nymph extends the labium very rapidly to seize its prey, taking only 15-40 milliseconds to snatch its victim with its pincers before they can react and escape. By contrast a human blink lasts on average 100-150 milliseconds. Once captured, the labium is drawn back towards the head, and the nymph will devour its prey using a set of powerful mandibles that can easily deal with the flesh of fish and tough Cuticles of insects.
Once the aquatic larval phase ends, adult dragonflies and damselflies leave the water and take to the air, where they are excellent and acrobatic flyers. Hunting other insects on the wing, they do not eat carrion or vegetation, although there are occasional reports of both.
All Odonata have excellent vision; dragonflies notably have very large eyes, the largest of the insect world. The field of view covers almost 360°; with only a blind spot caused by the obstruction of the thorax and abdomen. They can detect colour, ultraviolet light, and can determine the polarisation of light which may be useful in identifying the reflective surfaces of water. In addition to their large compound eyes, Odonata have 3 Ocelli, a simple eye consisting of one lens, on the top of their heads which are thought to help maintain orientation while flying.
Their vision is sensitive to movement, and they can easily track fast moving insects as they fly. Odonata have a remarkable range of movement of the head and can often be seen perched on a reed or stem moving their heads rapidly, tracking likely food sources and other Odonates.
Their excellent vision, agility, and ability to hover, fly forward, sideways, and backwards, means that dragonflies and damselflies are well adapted to capture prey easily.
They are opportunistic hunters and eat what is available; they don’t have a preferred target, but flies are a typical meal. Larger dragonflies may take prey as big as damselflies and butterflies, and sometimes smaller dragonflies too. Damselflies usually concentrate on small flies and similarly sized prey but occasionally they will also prey on other damselflies.
Dragonflies and damselflies utilise three different strategies when searching for prey.
Odonata capture prey either by extending their legs in flight and using them as a kind of net or basket, or by using their mouthparts.
Larger dragonflies like Hawkers may capture and eat prey on the wing, but many species return to a perch to feed.
Dragonflies and damselflies don’t sting their prey; they have no stinging parts and eat their victims using powerful mandibles with tooth like serrations – Odonata means ‘toothed one’.
Odonata are apex predators in the insect world, but the both the larval and adult stages of dragonflies and damselflies have predators.
Dragonflies are aerial acrobats and able to avoid predation by many birds, but agile fliers like flycatchers and raptors will take them; they form an important part of the diet of the Hobby – Falco Subbuteo which may as many as 50 or even more dragonflies in a day. Other insects like Hornets can kill a dragonfly and will make short work of one. Damselflies being weaker and slower fliers offer an easier meal and damselflies especially are often captured in spiders’ webs. Odonata will also eat each other, with smaller species falling victim to larger ones.
A particularly dangerous time for Odonata is Emergence, where they can neither return to the water or fly. Because of this, dragonflies often emerge at night, presumably in an effort to avoid daytime predation by birds. Another technique used by some species is synchronised emergence, where large numbers emerge together. This effectively swamps a predator’s ability to focus on a single insect, and so helps cut down on the likelihood of an individual being eaten. However, frogs and birds will often try to catch newly emerged dragonflies and damselflies before their first flight while still in their teneral state, before their body and wings have fully hardened.
Nymphs are aggressive hunters, but they too will fall victim to larger predators. Fish, birds, diving beetles will all eat them, as will other larger Odonata larvae.
Odonata are also vulnerable to parasites; it’s not uncommon to see damselflies with external mite infestations, and larva and adults are hosts to many internal parasites.