The candle fly is a common name for insects in the family Fulgoridae, a group of large planthoppers found across tropical and subtropical regions. The most famous species, Fulgora laternaria, earned its name centuries ago from the widespread belief that its bulbous head glowed in the dark. It doesn’t. But the name stuck, and today “candle fly” and “lanternfly” are used interchangeably for these striking, sap-feeding insects.
Why It’s Called a Candle Fly
The name traces back to early European naturalists who encountered Fulgora laternaria in Central and South America and reported that its large, hollow head projection emitted light. The idea was plausible enough at the time. Across cultures, glowing insects inspired vivid folk names: Sicilians called fireflies “cannilicchia di picuraru,” meaning “little candle of the shepherd,” and people in Durham, England, referred to glow-worms as “fairy lanthorns.” Naming a strange tropical insect after a lantern fit the pattern perfectly.
The problem is that Fulgora laternaria has no bioluminescent capability whatsoever. True light-producing insects like fireflies generate their glow through a chemical reaction between two molecules, luciferin and an enzyme called luciferase, and they control the process by regulating oxygen flow to specialized cells in their abdomen. The candle fly lacks this entire system. Scientists have never observed it producing light under any conditions. The myth likely started with a single early account and was repeated so often it became accepted fact, even making its way into the species’ Latin name: “laternaria,” meaning lantern-bearer.
Size, Appearance, and That Strange Head
Fulgora laternaria is a large insect, reaching 85 to 90 millimeters in body length (roughly 3.5 inches) with a wingspan of 100 to 150 millimeters (4 to 6 inches). Its most distinctive feature is the hollow, bulbous extension on its head, which juts forward 10 to 15 millimeters and looks remarkably like a peanut shell. This protuberance has patterns that resemble the eyes and snout of a lizard or small snake, which likely deters birds and other predators that would rather not tangle with a reptile.
The rest of the body is built for camouflage. During the day, candle flies sit motionless on tree trunks, where their mottled brown and green forewings blend with bark. If a predator gets too close despite the disguise, the insect has a backup plan: it snaps open its hindwings to reveal large, bright yellow eyespots that startle the attacker. At the same time, it releases a foul-smelling chemical. Between the fake snake head, the surprise eyespots, and the stench, candle flies have a layered defense system that compensates for their lack of speed or venom.
How Candle Flies Feed
Like all planthoppers, candle flies are herbivores that feed exclusively on plant sap. They have a specialized mouthpart called a rostrum, which works like a hollow needle. The insect pierces bark or plant tissue and drinks the sugary fluid flowing through the plant’s vascular system. Because plant sap contains far more sugar than protein, these insects consume large volumes and excrete the excess sugar as honeydew, a sticky liquid that coats surfaces beneath feeding sites.
In young planthoppers, these sugary secretions can also form waxy, tail-like filaments that trail from the body. The honeydew itself plays a role in the broader ecosystem. It feeds ants, wasps, and fungi, including sooty mold, which can coat leaves and reduce a plant’s ability to photosynthesize. A heavy infestation of sap-feeding planthoppers on a single tree can visibly weaken it over a growing season.
Preferred host plants vary by species and region. Tropical candle flies favor large hardwood trees, while their relatives in temperate zones feed on a wider range of vegetation including shrubs, grasses, and ornamental trees. Native wattles, grapevines, and various tree species all serve as hosts depending on what’s available.
Life Cycle and Reproduction
Most Fulgoridae species complete one generation per year. Adults mate and lay eggs in autumn, and those eggs overwinter before hatching in spring. Females deposit egg masses on tree trunks, plant stems, rocks, fence posts, and even vehicles or outdoor equipment. Each egg mass contains between 20 and 50 eggs, and a single female typically lays at least two egg masses before cold weather arrives. On a nutrient-rich diet, females can produce closer to 95 eggs total across multiple masses.
After hatching, nymphs pass through four developmental stages (instars) before reaching adulthood. This process takes roughly 70 to 90 days depending on diet and temperature, with nymphs feeding on a wider variety of plants reaching maturity faster than those restricted to a single host. The nymphs look nothing like the adults. They’re small, wingless, and often brightly colored in black and white or red patterns that signal toxicity to predators. Each molt brings them closer to their adult form, with wing pads gradually developing through the later stages.
Adult lifespan is relatively short. In temperate regions, adults live roughly 6 to 7 weeks before the first hard frost kills them. Those feeding on preferred host plants tend to survive longer than those stuck on less nutritious alternatives.
Role in the Ecosystem
Candle flies sit in the middle of their food web. They feed on plants and, in turn, become prey for spiders, birds, lizards, and predatory insects. Their presence in a habitat reflects the health of the vegetation layers they depend on, particularly shrubs and mature trees with accessible bark. Areas with diverse native plant communities support more planthopper species and larger populations.
The relationship between candle flies and their environment becomes a problem when species end up outside their native range. The spotted lanternfly (Lycorma delicatula), a relative in the same family, has become a serious agricultural pest in parts of North America since arriving from Asia. Without the natural predators and parasites that keep it in check at home, it feeds aggressively on grapevines, fruit trees, and hardwoods. Native tropical candle flies like Fulgora laternaria haven’t caused similar problems, largely because they remain within ecosystems that evolved alongside them.
Their ecological value is easy to overlook because they’re quiet, slow-moving, and nocturnal. But as both consumers of plant sap and food for dozens of predator species, they’re a functional link between the energy stored in trees and the animals that patrol the forest canopy and understory.