Many people naturally wonder if dragonflies are flies since they have many similarities at first glance and have similar names. If you’re wondering this too, this post will help.
Dragonflies and flies are unrelated insects. Dragonflies are much larger than flies and have four wings compared to flies which have only two wings. Flies undergo complete metamorphosis while dragonflies undergo incomplete metamorphosis. They live in different habitats and have different lifestyles.
Dragonflies and flies are superbly adapted to their respective niches in the natural world and each would starve to death if forced to live the other’s lifestyle. Below is a table that summarizes several important differences between the two insect Orders. Because the terms “dragonfly” and “fly” both cover a huge and diverse variety of creatures, I’ve narrowed each insect type to an example species to illustrate the differences.
Overview of the differences between dragonflies and flies
| Dragonflies | Flies | |
| Order | Odonata (oh-doh-nah-tah) – means “toothed” | Diptera (dip-tair-ah) – means “two-wings” |
| Approximate number of worldwide identified species | 5,600 | 150,000 |
| Size range | 1.4 – 3.7 inches (3.6 – 9.4 cm) | 0.28 – 0.31 inches (0.7 – 0.8 cm) |
| Body shape | Long, thin body with large head and thorax and elongated abdomen tapering to a point | Short and compact, thorax and abdomen about the same length |
| Wing configuration | Two (2) pairs of large, elongated membranous wings. Wing pairs are similarly sized. Wings are held at approximately 90 degrees to the long axis of the body at rest, within the same plane. All wings contribute to powered flight and maneuverability. | One (1) pair of tapered membranous wings. Hind wing pair are vestigial sensory organs called “halteres”. Wings are held at approximately 30 degrees to the long axis of the body at rest, within the same plane. Only the fore wings contribute to powered flight. Halteres stabilize the body and send sensory information about air currents and speed during flight. |
| Mouth structure | Chewing | Mostly sucking, sponging and lapping. Some species chewing. |
| Leg structure | Perching, grasping | Walking, standing |
| Colors | Species and sex dependent. Can be bright blue, green, yellow, bright red, brown and black. Wings can be transparent or translucent or display dark patches. | Species dependent. Thorax is striped with black and gray, abdomen is brown. Wings are translucent. Some species can be iridescent green or blue. |
| Common habitat | Specialist: Lakes, ponds, quiet portions of rivers with heavy vegetation | Generalist: All areas associated with humans and human-raised livestock (“synanthropic”) |
| Lifestyle | Predator | Scavenger |
| Development | Incomplete metamorphosis (“hemimetabolism”) | Complete metamorphosis (“holometabolism”) |
| Species example | Libellula vibrans (“Great Blue Skimmer”) | Musca domestica (“House fly”) |
Dragonflies and flies have different body shapes
A dragonfly’s body is very long and thin, with a large thorax (where the legs and wings attach) and a narrow, extended abdomen. A fly’s body is much shorter and stockier overall.
Dragonflies and flies are different sizes
They are also very different sizes. Dragonflies are huge compared to flies; the Great Blue Skimmer is about eight times bigger than a House Fly. In fact, dragonflies may be as big and heavy as an insect can become and still fly in today’s atmosphere.
Dragonflies and flies are different colors
Dragonflies come in a dazzling array of colors, including brilliant greens, browns, blues and reds. Male Great Blue Skimmer dragonflies are a striking pale blue with bluish-green eyes, while females are a reddish brown with a black stripe down the abdomen.
House Flies, on the other hand, are mostly black and gray, although they can appear tinged with green in certain lights. Other fly species may show iridescent green and blue coloration but in general, flies are much duller.
Dragonflies and flies have different wing configurations
After size, the number of wings and how they are positioned are probably the most visible differences between the two types of insects. All dragonflies have four wings; all flies have only two.
Dragonflies hold their wings straight out horizontally, which gives them a distinctive t-shaped silhouette. Flies have only two wings which lie on top of their thorax and extend slightly out to the side in a triangular silhouette.
Dragonflies and flies fly differently
The wing differences go beyond the cosmetic; the two types of insects actually fly differently.
The Great Blue Skimmer – like all dragonflies – flaps its front wings independently from its hind wings, which lets each pair catch undisturbed air.
Additionally, the dragonfly twists each wing on the down stroke of each flap, “creating miniature whirlwinds that allow air to move much faster over the upper wing surface, reducing the air pressure there and greatly increasing lift.” (Imes 1992, 68)
This is a unique mode of flight in the living world and has been studied extensively. The House Fly flies in a more usual manner, flapping both wings at the same time to generate lift.
Dragonflies are fighter pilots; flies are acrobats
Both dragonflies and flies are superb aerialists and can hover, fly backwards and change directions in midair faster than the human eye can follow.
But the House Fly can perform an acrobatic trick that the Great Blue Skimmer can’t – it can turn itself upside down in midair.
A House Fly beats its wings much faster than a dragonfly does – approximately 1000 beats per second versus a dragonfly’s 20-40 (Tenneson 2009). When combined with lightning fast information about air currents and the insect’s position in space supplied by the halteres, this fast wing speed allows a House Fly to flip itself over completely in mid-air without falling from the sky.
Flies usually perform this maneuver to land upside down on a surface. Their clawed feet are outfitted with special pads covered in sticky secretions which grip the landing surface. These adaptations allow House Flies to cling securely to nearly any surface.
By contrast, dragonflies must stay upright.
Dragonflies may not be able to turn somersaults on the wing but they are speed demons in the air. Dragonflies can zoom around their territories at speeds up to 35 miles per hour (56 kilometers per hour) (Imes 1992, 68).
The House Fly flies at a comparatively pokey average speed of about 4.5 miles per hour (7.2 kilometers per hour) (Dahlem 2009).
Dragonflies and flies have different mouths
Dragonflies are skilled predators who actively hunt on the wing, snatching flying insects out of the air. Their jaws (or “mandibles”) are large, serrated and powered by strong muscles perfect for slicing through the hard exoskeletons of their insect prey.
On the other hand, House Flies are scavengers that feed on decaying organic matter by lapping up liquid. They have no need for strong jaws like the dragonflies so their mouths have developed sponging mouth parts instead.
Dragonflies perch; flies walk
Both the Great Blue Skimmer dragonfly and the House Fly can perch on their hind-most four legs and use their front legs to perform various tasks. The Great Blue Skimmer uses its front legs to hold and manipulate prey, whereas the House Fly uses them to clean dust and debris off its body bristles.
But flies and dragonflies move very differently when grounded; flies can move easily across a surface while dragonflies have difficulty moving at all.
The Great Blue Skimmer’s legs are crowded together towards the front of the thorax, which is a feature of all species within Order Odonata. This adaptation is necessary to allow enough space for the huge flight muscles needed to power the dragonfly’s long, narrow wings.
The positioning of its legs allows the Great Blue Skimmer to swing all six legs forward during an attack on prey, scoop the insect out of the air and grip it until the dragonfly can grab it with its jaws. But this clustered arrangement limits the mobility of its legs when not in the air and prevents the dragonfly from walking easily.
For more information, check out this Now I Wonder post “Can dragonflies walk?“.
By contrast, the House Fly can walk easily as its leg are widely spaced and adapted for moving around on foot. A House Fly has two choices for moving from one location to another; it can either walk or fly. Dragonflies don’t have this choice; a Great Blue Skimmer has to fly to get anywhere at all.
Complete versus incomplete metamorphosis
Dragonflies undergo incomplete metamorphosis, which means that they share some of the same physical structures at all life stages. An immature Great Blue Skimmer can be recognized as a “dragonfly” if you know what to look for.
But a House Fly undergoes complete metamorphosis; flies look completely different at every stage, from larval, through pupal and ending in the adult form. Some people are familiar with the larval fly form (otherwise known as “maggots”) and most are familiar with the winged adult form. But it would be difficult to tell that a maggot is a “fly” just on the basis of how they look.
Dragonflies are good neighbors; flies cause problems
Dragonflies and flies live very different lifestyles.
Dragonflies are usually found near quiet, fresh water where there are plenty of flying insects to chase down and eat and don’t bother people. Some people may be taken aback by their sheer size but any physical contact is purely accidental.
Dragonflies cause no harm to humans; in fact, they can be beneficial due to eating enormous numbers of insects that do cause humans harm, such as flies.
Flies are found worldwide in all habitats because their food is easy to come by. As scavengers, they only need to zero in on a source of their preferred food, land, and begin feasting.
Unfortunately, flies are not picky; they are as happy to land on your lunch as on a rotting rat and perfectly content to alternate between the two.
Flies can and do hurt people despite being admirable in many respects. Some species, like the House Fly, can transmit diseases by landing on decaying organic matter and transporting dangerous microorganisms on their sticky feet. Other fly species such as black flies, horse flies, and deer flies evolved biting mouth parts, which they use on humans.
Different insects; fascinating abilities
Dragonflies and flies are totally different creatures who have different skills, behaviors and lives. But they share one very important trait – they are both fascinating residents of the natural world.
Related Now I Wonder Posts
For more about dragonflies and other insects in order Odonata, check out these other Now I Wonder posts:
- Can dragonflies walk?
- What do dragonflies do at night?
- What is the difference between a dragonfly and a damselfly?
For information about insects in general, check out these other Now I Wonder posts:
- Do insects ever eat spiders? Part 1: Attacks from the air
- Do insects ever eat spiders? Part 2: Attacks from the ground
- Do insects have blood?
References
Dahlem, Gregory A. “House Fly.” In Encyclopedia of Insects, edited by Vincent H. Resh, and Ring T. Carde. 2nd ed. Elsevier Science & Technology, 2009.
Imes, Rick. 1992. The Practical Entomologist. London: Quarto Publishing.
Meyer, John. North Carolina State University, NC State General Entomology, https://projects.ncsu.edu/cals/course/ent425/library/compendium/odonata.html
Tennessen, K. J. “Odonata.” In Encyclopedia of Insects, edited by Vincent H. Resh, and Ring T. Carde. 2nd ed. Elsevier Science & Technology, 2009.