Understanding Dragonflies and Fireflies: A Quick Guide
Dragonflies and fireflies are some of the most well-known insects in the United States.
Dragonflies are easily recognized by many people thanks to their large size, bright colors, and incredible flying abilities. Fireflies are famous for the surreal light shows they put on across the eastern United States.
But despite sharing many basic characteristics which makes them “insects”, they are far more different from each other than similar.
Dragonflies and fireflies are both insects but differ in size, anatomy, behavior, life cycle, habitat, means of defense against predators, and number of known species. Dragonflies are classified in order Odonata, suborder Anisoptera. Fireflies are beetles in order Coleoptera, family Lampyridae.
Both dragonflies and fireflies are fascinating creatures that can add a lot to your enjoyment of the natural world. They are both common insects, so learning more about them is worthwhile as understanding their differences can help you appreciate them.
Approximately 336 dragonfly species (Paulson, 2014) and 81 firefly species (Evans, 2014) live in the eastern United States and Canada. Read on to discover the differences between these two kinds of insects.
How to tell dragonflies and fireflies apart
Physical appearance of larval dragonflies
Larval dragonflies share some physical characteristics with adult dragonflies, although they look very different. Their bodies are clearly segmented into head, thorax, and abdominal sections. They have large eyes like the adults, but are tiny compared to the adults, have only wing buds, and are dull brown.
Physical appearance of larval fireflies
Larval fireflies are multi-segmented and look a little like flattened, armored worms or caterpillars. Their heads are hidden from above by the exoskeleton of their first thoracic segment, and their antennae are short and stubby.
Like the adult forms, firefly larvae produce light in their final abdominal segment, which is why they are called “glow worms”.
Physical appearance of adult dragonflies
Adult dragonflies are large, conspicuous insects. The largest adult dragonfly species found in the southeastern United States reach up to 9 cm (3.5 in) in length and have wing spans of nearly 6 cm (2.4 in).
Like all insects, adult dragonfly bodies consist of three segments protected by hard exoskeletons: the head, the thorax, and the abdomen. But dragonflies have a unique silhouette that is unmistakable, once you know what to look for.
Dragonfly Heads
Extremely large compound eyes and strong, chewing jaws dominate their heads. Each eye is composed of thousands of individual lenses, each of which sends a slightly different picture of the dragonflies’ surroundings to their brains. In most dragonfly species, the two eyes meet in the middle of their heads and provide nearly 360 degree vision. Dragonflies also very small, simple eyes that see changes in light.
Unlike many other insects, such as fireflies, adult dragonflies can move their heads around quite a bit. This helps them continuously monitor their surroundings and makes these insects very hard to sneak up on. Dragonflies do have antennae but they are short, stubby, and nearly invisible except when magnified.
Dragonfly Thoraxes
The thoracic segment bears the dragonflies’ wings and legs. Dragonflies have two pairs of long, thin, transparent wings that they hold out to the side at rest, never folded. Some species sport blotches and patches on their wings that differentiate them from others. Their six legs are also long and thin and are covered with spines that trap prey.
Dragonfly Abdomens
Ten individual segments form dragonflies’ long, thin abdomens and end in structures that dragonflies use during mating. In general, female dragonflies have slightly shorter, thicker abdomens than males because of their egg-laying organs. The males of some species have club-shaped abdomens, such as the aptly named clubtail dragonflies.
Dragonflies come in every color, from shades of gray and black to bright yellow, red, green, blue, and orange. Their bodies can be striped, spotted or ringed by different colors. Males and females of the same species can differ in color, as can young and old adults.
Physical appearance of adult fireflies
Compared to dragonflies, which vary in size, color, and wing patterns, adult fireflies are much more standard, even across different species.
Adult fireflies are small insects, usually 5-20 mm (0.2 – 0.8 in) long. Their bodies are softer than those of dragonflies; their exoskeletons are more leathery than hard. Overall, fireflies are brown-black with light-colored markings. An enlargement of their first thoracic segment hides their heads from above and is nearly as wide as their bodies. A red, yellow, and black spot decorates the hood in some species and helps differentiate species.
Lifecycle and behaviors
Both dragonflies and fireflies hatch from eggs. The larvae of both species eventually mature into adults but they start life in different places.
Lifestyle and behavior of dragonfly larvae
Dragonfly eggs hatch underwater and breathe through special gills in their abdomens. The immature insects, known as “naiads”, spend many months living on the bottom of lakes, ponds, streams, and rivers. Naiads are well-suited to their aquatic habitats. They crawl around underwater but have the unique and surprising ability to jet forward by squirting water out of their abdomens under high pressure.
All dragonfly naiads are predators. They actively hunt aquatic invertebrates, tadpoles, small fish, and even their fellow dragonflies. Their mouth parts are specially modified to shoot forward at high speed. Their jaws spring out so fast their prey can’t react and evade the attack. The naiads’ jaws clamp onto the prey, then retract back to their heads, where the prey is eaten.
Lifestyle and behavior of adult dragonflies
Dragonflies are relatively long-lived insects, living for several months in the southeastern United States between late spring and early fall, depending on the species. All adults are carnivorous, without exception. They spend much of their time in flight, hunting a wide variety of flying insects, which they capture in mid-air, locating suitable mates, and mating.
Dragonflies are famously fast and agile fliers, able to obtain straight-line speeds of up to 35 mph (56 km/hr), reverse direction within one body length, hover, and fly backwards and upside down with ease (Imes 1992). This skill serves them well to chase down flying insects for food and flee predators.
Lifestyle and behaviors of firefly larvae
In contrast, firefly larvae are entirely terrestrial; their eggs hatch underground and the larvae emerge to grow and develop on dry land. Also predators, firefly larvae actively hunt snails, slugs, earthworms, and also attack their fellow fireflies. But instead of hunting underwater, firefly larvae hunt under leaf litter or in low-growing vegetation.
Firefly larvae attack their prey with strong, sharp mandibles. But they lack the dragonfly larvae’s extendable jaws and don’t kill their prey by biting it apart. Instead, firefly larvae poison their prey. Toxic biochemicals flow down special channels in their mandibles. This venom paralyzes the prey first, then liquefies its tissues (Evans, 2014).
Lifestyle and behavior of adult fireflies
Many firefly species fly well, but the females of some species, such as females in genus Photinus, fly weakly or not at all. Fireflies have only one pair of flight wings. These are membranous and folded carefully away under their hind wings when at rest. Their hind wings are leathery and protect the flight wings at rest. During flight, they serve as airfoils to stabilize and steer the insects’ flight.
Species that fly well are active at dusk and at night, when the light they produce is most visible, and hide from predators during the day. Flightless species, or those that don’t light up, such as those in genera Ellychnia, Lucidota, and Pyropyga, are more active during the day and can be found in vegetation (Evans 2014).
Dragonfly and firefly enemies
Despite being voracious and powerful predators for their size, many animals attack and eat dragonflies during all life stages. These include aquatic predators such as large fish, frogs, and ducks that feed on the naiads. Predators of adult dragonflies include orb-weaving spiders, insect-eating birds, lizards, and other predatory insects.
Dragonfly defenses
To avoid predators, dragonfly nymphs hide under cover or shoot themselves out of reach by squirting water out of their abdomens under pressure. Adult dragonflies rely on their superb vision and flying abilities to zoom out of predators’ reach. Dragonflies must rely on their physical abilities to stay alive.
Firefly defenses
In contrast, many firefly species can sicken or kill predators if eaten. They manufacture a toxin “lucibufagin”, that they store in their body tissues (Berger et al., 2021). Not every firefly species can manufacture this chemical; those that lack this ability obtain them second-hand by eating their cousin species that can.
When threatened, fireflies exude the toxic lucibufagin from special weak points in their exoskeletons, like their leg joints. This defense mechanism is known as “reflex bleeding” and is one that fireflies share with other beetle species, such as ladybugs (family Coccinellidae).
Fireflies advertise this chemical defense visually by using their most famous ability – bioluminescence. Individuals of all ages can generate light using two special chemicals called “luciferin” and “luciferase”. They mix these two enzymes together at will. The combination creates visible light. Both firefly larvae and adults use this light to warn potential predators against attacking them. In addition, adults light up to attract mates.
Unfortunately, the visual light warnings and toxic body tissues are insufficient to prevent all predatory attacks. Fireflies are still vulnerable to predators such as orb-weaving spiders (Araneidae) and harvestmen (Phalangiidae) (Faust, 2010).
Mating and Reproduction
Dragonfly reproduction
Dragonflies live their adult lives within flying distance of ponds, lakes, rivers, and streams.
They must lay their fertilized eggs in water. They rely on their acute vision to identify same-species members of the opposite sex from a distance. Most dragonflies mate in the air. Males will fly in pursuit of females, clasp them firmly around the head with their abdominal claspers, and fertilize their eggs in flight. The females then fly over water and lay their eggs by dipping their abdomens under the surface. In many species, the males continue to grip the females while the females lay the eggs.
Firefly reproduction
In contrast, fireflies mate on the ground or in vegetation, rather than in flight. While they rely on vision to locate mates, they use a much different method than dragonflies.
Fireflies search for mates at night when their ability to produce light on command is most useful. Fireflies are drably colored and mostly brown or black. But every firefly species lights up in a particular color and pattern unique to that species.
Males and female fireflies arrange themselves at different levels within their woodland or meadow habitats; males fly several feet above the ground vegetation, where females perch. The males flash their abdomens and search the vegetation below them for an answering light signal created by the females. The males zero in on the answering flashes and fly into the vegetation to encounter the females.
Femme fatale fireflies
Most of the time, this mate location strategy works well; a male of one species intercepts a female of the same species, thanks to their coordinated, species-specific flash pattern, and the two mate.
But some species of predatory fireflies evolved the ability to mimic the flash pattern of others. Most adult fireflies do not feed. Females belonging to the Photuris genus are the exception. They eat males of other firefly species (Maquitico et al 2022).
These “femme fatale” firefly females trick males of other genera into landing nearby by mimicking the light pattern of those males’ own females. For example, Pennsylvania fireflies (Photuris pennsyvlanicus) mimic the flash pattern of Big Dipper fireflies (Photinus pyralis). The predatory females lie in wait in vegetation and flash the trick signal at the overhead males to tempt them close. When the hapless pyralis males wing in expecting to find mates, the Pennsylvania females attack.
This is an excellent survival strategy for the photurid females. They can’t manufacture their own defensive biochemicals but obtain both nourishment and lucibufagin by eating their cousin species, which can.
Where to go from here
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References
Berger, Andreas, Georg Petschenka, Thomas Degenkolb, Michael Geisthardt, and Andreas Vilcinskas. 2021. “Insect Collections as an Untapped Source of Bioactive Compounds—Fireflies (Coleoptera: Lampyridae) and Cardiotonic Steroids as a Proof of Concept.” Insects 12 (8): 689.
Evans, Arthur V.. 2014. Beetles of Eastern North America. Princeton: Princeton University Press.
Faust, Lynn Frierson. 2010. Natural History and Flash Repertoire of the Synchronous Firefly Photinus Carolina (Coleoptera: Lamyridae) in the Great Smoky Mountains National Park. The Florida Entomologist 93 (2) (06): 208-217
Imes, Rick. 1992. The Practical Entomologist, New York (NY): Quarto Publishing plc.
Maquitico, Yara, Aldair Vergara, Ilana Villanueva, Jaime Camacho, and Carlos Cordero. 2022. “Photuris Lugubris Female Fireflies Hunt Males of the Synchronous Firefly Photinus Palaciosi (Coleoptera: Lampyridae).” Insects 13 (10): 915. doi: https://doi.org/10.3390/insects13100915.
Paulson, Dennis. 2012. Dragonflies and Damselflies of the East. Princeton: Princeton University Press.
