What do Dragonflies Eat?
A Story of Prehensile Jaws, Butt Propulsion, and Biting Mouth Bits
Dragonflies are one of those creatures that people love and hate. They show up on Memaw's knitted sweater, baby onesies, wine glasses, and summer napkins, but when it comes to actually seeing them in the wild many people cringe. They're fast moving, multi-winged, and bug-eyed creatures that look like aliens. Two of the most common questions I get asked is "Do dragonflies bite?" and "What do dragonflies eat?" In this blog we'll cover both questions, and the extraordinary world of dragonfly feeding, from prehensile jaws to mandibles.
WHAT IS A DRAGONFLY?
A dragonfly is an insect in the order Oodonata (Oh-da-nah-da), which means "toothed one" (we'll get back to this) . The dragonfly that you probably think of when you're conjuring granny's sweatshirt, or your plastic hair-clips from elementary school, are the adult dragonflies. Adults have big compound eyes with over 29,000 lenses that can see all around their heads, which aid in hunting for insects while sitting or flying. They have a strong thorax (middle bit) that has two sets of wings attached. These wings are held straight out, horizontally, at all times and the wings are uneven. The back ones are broader for stability and maneuvering. This wing size difference is what puts dragonflies in the infraorder Anisoptera (Greek for "unequal wing").
WHAT DO ADULT DRAGONFLIES EAT AND DO THEY BITE?
If you look at the face of a dragonfly they look like a cross between an insect, Gomez Adams from Adams Family, and flying a ninja. Check out the picture below.
You can see the big compound eyes easily, and they have two tiny antennae that look like Gomez's mustache, and then their mouth bits. These mouth parts are the business end of things that help address the question, "What do dragonflies eat?"
I'm not going to go into the technical biological labels of upper and lower lips and seams, sutures, frons, or plates. The main thing to notice is that they have jaws that work side to side and that are shaped like wicked meat hooks, mandibles (man-dibbles) that go up and down and maxillae (max-ill-eh) that act like a lower lip and hold food. Their curved jaws are for piercing and holding insects while flying and also for defense. Remember, dragonflies are in the order Oodonata, which means "toothed-one." This is the Greek reference to their "toothed" or serrated jaws. They most certainly can bite, as attested to a friend that once got a big dragonfly too close to her nose. However, they don't want to bite humans and only do so as a last defense if captured.
All adult dragonflies are insectivores, which means they eat insects they catch with their spiney hairy legs. The insects are then held in a basket-like device while flying. They particularly delight in mosquitoes (30-100+ per day per dragonfly!) as well as other pesky flight bugs such as flies, butterflies, bees, and even other dragonflies. Dragonflies eat while flying and hunting at high rates of speed too, which is an incredible feat.
BUT WAIT THERE'S MORE! BUTT BLASTERS AND PREHENSILE JAWS OH MY!
Now here's my favorite part of answering the question, "What do dragonflies eat?" We've talked about Memaw's favorite sweater and adult dragonflies, but that's only half the story. You see, those adult dragonflies start out life, as all dragonflies do, living in water as aquatic wee beasties. Female dragonflies lay their eggs in water and then the eggs hatch into the unholy terrors of the freshwater world. At this stage they are called nymphs. Now don't get any ideas that these are beautiful nymphs frolicking through the water like Greek goddesses...nope, more like Gorgons! Take a look below.
Dragonfly nymphs are voracious hunters, eating everything in sight that moves, even things bigger than they are!! This includes tadpoles, fish, aquatic insects, worms, and more. They're crucial predators in the underwater world, and yes, they can bite at this stage too, though to me it doesn't hurt as much as the adults and it takes a lot to provoke one to bite.
Dragonfly nymphs have prehensile (pre-hen-sigh-el) mouth part. Prehensile just means capable of grasping or seizing. This prehensile bit, called the labium (lay-be-um) is attached just below its mandibles and eyes, and is hinged so that it can fold flat against the body. The end of the labium has two serrated teeth, much like an adults' fierce meat hooks, and these fold up to form a face mask when not in use. The effect is that of a ninja's face mask covering the lower portion of its face. The nymphs sit and wait for prey. When they see something munchy, their jaws shoot out within three one-hundredths of a second! The hooks snag the prey like something out of the movie Alien and drag it back to the mandibles and chewing mouth bits. Watch this video:
But that's not event the crazy part. The dragonfly nymph's jaw movement is driven by high-blood-pressure-hydraulic-jet-propulsion from its butt! The dragonfly draws water into its anal opening, compresses its muscles in the water-filled butt-chamber against the muscles in the fluid-filled body chamber (not really blood but close enough), which raises the body's blood-pressure, and pushes out the labium in a rapid strike. This is about 0.87 psi (pounds per square inch), which is huge! They can also use this butt-pressure chamber to propel them through the water too, and the thrust is nearly 10 cm/second.
So, what do dragonflies eat? As adults they eat flying insects such as mosquitoes, flies, and bees while as juveniles they eat anything from tadpoles and fish to aquatic worms and invertebrates. Can dragonflies bite? Yes, in both aquatic and adult forms, but they don't want to, they simply want to hunt food and get along with their flying or high-blood-pressure-hydraulic-jet-propulsion-backside hunting.