Beneficial Insect — Firefly
Fireflies or 'lightning bugs' as some people call them are some of our most celebrated insects.
Spring is here, which for much of the country means fireflies are starting to wake up. For many
of you, late spring and early summer are synonymous with fireflies. Shaking off the dormancy of
winter, the larvae of flashing fireflies typically mature into adults in May or June.
Females perch on vegetation or sit on the ground while males take flight, flashing their abdomens and awaiting
a response from below. Flash–wait–flash. Repeat. This call and answer routine is how many firefly
species find mates. For the humans among us, it could just as well be a magic show, a glimmering
peek at one of the great wonders of the natural world.
Light Pollution Is The Biggest Threat To Fireflies
Fireflies communicate in a language of light. They flash to signal for mates. Scientists believe they
also flash to drive away predators, claim territory, and communicate with others of
their species as well
Without their flashing lights, there could be no fireflies!
In rural areas where the only night lights once came
from the moon and stars, suburban sprawl has brought extensive exterior lighting
along roads, in private yards, and in commercial centers.
Firefly behavior has been observed to be affected by bright lights at night. Fireflies typically won’t
make an appearance where there are bright ambient lights, such as full moon evenings. If
artificial light interrupts the fireflies’ ability to signal each other which can disrupt mating — meaning fewer
fireflies will be born each year.
Fireflies have immense cultural, biological and
economic importance and are important components of natural ecosystems. Their public appeal
makes them an ideal flagship for conservation.
Who hasn’t chased a blinking firefly on a warm summer night? As children, we captured their luminescence
in glass jars to make insect lanterns. Unfortunately, these beacons of childhood seem to be disappearing
due to habitat loss and the interference of manmade lights.
There are a number of different species of fireflies, none of which are actually flies — they’re beetles.
They get the names “firefly” and “lightning bug” because of the flashes of light they naturally produce. This
phenomenon is called bioluminescence, and the bioluminescent organs in fireflies are found on the
underside of the abdomen. A similar group of organisms are glowworms. The term “glowworm” can refer to
firefly larva or wingless adult females—some of which are not in the firefly family Lampyridae. Both
glowworms and fireflies are bioluminescent. The important distinction is that fireflies have wings and
glowworms do not.
Anecdotal reports from around the world tell us of firefly declines. While the extent of declines and
their causes are not well understood, we do have a basic understanding of the major threats:
Habitat degradation and loss
Poor water quality
Fireflies may be most vulnerable during their larval stage, which can last up to 2 years. Adults, on the
other hand, are generally active for on a few weeks each year. Species with specific habitat
requirements or patchy distributions are often more at risk.
For example, species requiring true dark for their mating displays will be more affected by light
pollution. Species with flightless females may be more vulnerable to local extinctions since these
females cannot disperse very far. Lower water tables, an increasingly common issue due to
groundwater withdrawals or drier climates, can reduce the most habitats that fireflies need. Threats to
soft-bodied invertebrates such as earthworms, snails and slugs may have cascading effect on firefly
populations as they make up the majority of firefly diets.
Fireflies contribute to the food-web stability, playing important roles as both predators and prey.
Firefly larvae are voracious carnivores, feeding on a variety of soft-bodies invertebrates, including
snails, slugs and earthworms. Because of their large appetites and preference for snails and slugs,
fireflies can be highly beneficial in gardens and agricultural settings.
Most fireflies are toxic due to defensive compounds known as lucibufatins (LBGs). LBGs are highly
toxic substances that protect them from many predators including birds, toads and lizards. Yet,
despite the bad taste afforded by these chemicals and the warning glows and cautionary colors,
fireflies contribute to the diet of a number of animals.
Like all beetles, fireflies undergo complete metamorphosis with four distinct states: egg, larva, pupa
and adult. Most of their life cycle is spend in the larval stage: they spend up to 2 years as larvae, but
adults typically live for just 2 to4 weeks. The complete life cycle can take up to 2 to 3 years in the
northern United States.
After mating, females lay their eggs in most soil, diff, leaf litter or rotting wood. Eggs, which may glow
dimly, are deposited in batches or singly during period ranging from several days to weeks.
Two to three weeks later, these eggs hatch into grub-like beetle larvae that live in leaf litter,
underground or in rotting wood. All firefly larvae are bioluminescent, an adaptation thought to warn
potential predators that they are distasteful. The larvae become inactive in northern climates during
winter months. Although firefly larvae are rarely seen, the intermittent glow of foraging larvae can
sometimes be seen on dark nights in fall and spring.
Firefly larvae are voracious predators. They typically hunt for their prey in moist soils or marshy
areas near springs, ponds or creeks. Fireflies use their mandibles (jaws) to inject prey with
paralyzing neurotoxins and then secrete digestive enzymes that liquefy the prey
When fully grown, most firefly larvae pupate underground or in rotting logs. Depending on
temperature and species, pupation can last 1 to 3 weeks. Firefly adults typically emerge in late spring
or early summer.
All members of the family Lampyridae creates light using the same biochemical reaction which takes
place inside both larval and adult light organs (lanterns). A firefly enzyme, luciferase, allows it substrate,
luciferin, to interact with oxygen to produce light. This light-producing talent is thought to have evolved
as a warning signal that alerted potential predators to their distasteful or toxic compounds.
Different firefly species can emit different colors (wavelengths) of light varying from green to yellow to
Because most fireflies do not eat once they become adults, their reproductive activities must be
fueled by whatever resources they have stored from larval feeding. Fireflies have long mating
durations with pairs remaining coupled for one to several hours. During this time, males transfer an
elaborate sperm-containing package known as a 'nuptual gift'. Both sexes
can mate multiple times.
Mating flash displays occur during courtship. To attract the attention of females, flying males emit a
particular flash pattern while patrolling an area. Females generally do not fly, but instead perch on
low vegetation or on the ground. If she is interested, she will respond to the male by flashing back.
The flash dialog can continue for more than an hour until the male finally located the female and they
Most firefly researchers agree that habitat loss and degradation in addition to light pollution,
pesticide use and climate change are the leading threats to fireflies. Some of the most effective
strategies for conserving fireflies include identifying, protecting and restoring high-quality habitat.
Abundant larval foot sources such as snails, slug and earthworms
Safe places to over-winter including trees, leaf litter and underground burrows
Clean sources of water or moisture
Protection from insecticides
Native vegetation of varying heights
Do a self-audit of artificial light at night. Simple actions like closing blinds or curtains at night,
switching to timed lights, or installing shields on porch lights, can dramatically reduce the artificial
light at night that confuses, discourages, and drowns out fireflies.
Don’t use pesticides in your yard or garden. Pesticides applied to treat grubs or mosquitoes can
harm and kill fireflies and other insects and may degrade habitat or reduce firefly prey populations.
Investigate your town or city’s lighting ordinances and encourage leaders and policy makers to
adopt dark sky standards.
Encourage managers of local parks to make public green spaces as friendly for pollinators and
fireflies as possible.
You can help scientists track firefly populations by participating in a dedicated firefly program, or simply
by submitting photo observations to sites like iNaturalist.
Photos are important, but if you report a flashing firefly occurrence, remember to include some information
about its flash pattern. This will help with species ID, since so many flashing species can only be identified
by a combination of location, flash pattern, and physical appearance.
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