What do you call those insects that glow?
If you’re from the American South or surrounding regions, you probably call them lightning bugs. If you’re from the West or New England, you probably say fireflies. But there are exceptions, variations, complications, and half a dozen or so other names, including candlefly, firebob, and lamp bug. Whatever you call them, you probably remember them fondly from childhood—long June evenings spent chasing flickering, living stars.
If it seems like there aren’t as many of them as there used to be, it’s not your imagination
Introducing the Lampyridae
By any name, the little glowing insects are beetles. They are not just one species but thousands worldwide, in several different groups—the lampyrids, as they are known officially, are an entire family of beetles, meaning species of lightning bug can be as different from each other as a house cat is from a lion.
Most adult lampyrids glow at night in order to find mates; the color and the pattern of flashes indicate the species so that each insect can find a mate of its own kind. In one group, however, females can also mimic the flash pattern of other lightning bug species in order to attract prey (they do not eat males of their own species). Otherwise, lampyrid adults either eat pollen and nectar or do not eat at all, depending on the species. In some groups, females are wingless and signal males from the ground, while in others both sexes fly. There are also diurnal lampyrids that either don’t glow as adults or glow only weakly. These depend on pheromones, not light, to find mates.
All lampyrid larvae, regardless of species, glow (they do not flash). They live on or in the ground, where they eat slugs, snails, and worms. Despite being called “glow worms,” these young insects are not worm-like; they have strong legs.
The phrase glow worm can also apply to those females who remain flightless as adults, or to members of other glowing insect groups. In the American tropics and subtropics, the term is likely to refer to another beetle family, the phengodids. The phengodids also glow as larvae and as flightless adult females. Adult, flying males may also glow weakly. However, phengodids do not otherwise resemble fireflies and may or may not be closely related. There are other glow worms in other parts of the world, perhaps most notably a species of carnivorous, cave-dwelling fungus gnat in New Zealand.
Among lampyrids (and possibly among the various unrelated glow worms as well), the light is produced in specialized organs where a chemical called luciferin is allowed to mix with oxygen to become oxyluciferin. Then oxyluciferin reacts with the enzyme, luciferase, and glows. Adult lightning bugs can flash their lights by controlling the flow of oxygen to their light organs. Larvae and some flightless females glow steadily without flashing because they cannot control the oxygen flow.
The little lamps of lampyrids may be yellow, green, blue, or even red, depending on species. The flashes may be rapid or slow, calling attention to various display-flight patterns. Some species can synchronize their flashes; there are places in the world, such as parts of southeast Asia or a few pockets in the American South, where entire riverbanks flash on and off, or where waves of light sweep across whole hillsides. As to why fireflies are so much fun to catch—if you can get close enough to one before it vanishes back into the night it will land on your open hand—I’ve long suspected that the insects must either be poisonous or taste terrible and so have no predators, but like most people, I didn’t really know much about these familiar but mysterious little creatures. Then I set to researching for this article and it turns out I was right; don’t eat fireflies.
Conservation Concerns
Lampyrids are in trouble worldwide, but it’s difficult to be sure how much trouble. There are thousands of species, some of which may be doing alright while others may be critically endangered, and most have never been formally assessed. For most, nobody is sure that their populations are falling because nobody knows what their populations used to be. Very few people even know how to tell one lightning bug species from another. Unfortunately, lampyrids are not the only invertebrates for which such a lack of information is causing a problem; the living world is so diverse that even naming everything that’s out there is an overwhelming task, let alone figuring out which species need help.
Although in recent years some long-term monitoring of a few firefly populations has begun, the conclusion that lamprids are in trouble rests on a combination of indirect assessments—there is a large and growing number of anecdotal reports of population declines; other, better-studied insect groups are definitely declining; and many lampyrid species have characteristics well-known to be associated with vulnerability to extinction.
These vulnerabilities include:
- Specialized diets (if their few prey species die out of an area, the larvae can’t switch to different foods)
- Poor dispersal ability (if an area loses its fireflies, more can’t move in from a neighboring population)
- Vulnerability to pesticides (the larvae are carnivores, so they can accumulate large doses by continually eating contaminated prey)
- Requires darkness (light pollution is especially bad for species that use their lights to find mates).
What You Can Do to Help
The bad news is that our lovely living lights are in trouble, but the good news is that there’s plenty you can do to help them—this is not a situation where success depends on decisions made by a few powerful people far away. It’s another opportunity for conservation literally in your own backyard. Many species of lampyrid can do very well in urban and suburban environments, provided they get a little consideration for their needs.
Basically, just leave your yard a little messy.
And if you don’t have a backyard of your own, you can still advocate for firefly-friendly conditions in your community—you’ll be helping other, less visible, species with similar needs while you’re at it, too.
- Minimize pesticide use, and do not use broad-spectrum pesticides at all.
- Leave some fallen leaves and undisturbed, un-tilled ground where the insects can over-winter.
- Provide native vegetation of different heights (long grass, shrubs, wildflowers) and a source of water, both to protect and shelter the insects themselves and to shelter the slugs and snails the larvae need to eat. If the females of your local species are flightless, varied vegetation gives them good perches to display from, too.
- Turn off unnecessary outdoor lighting—security lights can be put on motion sensors—and advocate for reduced light pollution in your community.
For more information on helping our little glowing neighbors, contact the Xerxes Society. For more information about fighting light pollution, contact the International Dark-Sky Association. For information and support on naturalistic landscaping (and a handy-dandy yard sign to let your neighbors know you’re doing this on purpose!) contact the National Wildlife Federation’s Backyard Wildlife Habitat Program. And if you have a difficult time reducing or eliminating pesticides (perhaps your homeowners’ association disagrees or you wish to change the management policies at a local park) there are organizations that can help you, including Non-Toxic Communities.
It doesn’t matter if you call them lampyrid beetles or firebobs, the important thing is to decide whether you want your nights bright with living stars.
Caroline Ailanthus