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Beneficial Insect — Firefly

Firefly Fireflies or lightning bugs as some people call them are some of our most celebrated insects. They 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.

Fireflies In Decline

Firefly body parts graphic 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
  Light pollution
  Pesticide use
  Poor water quality
  Climate change
  Invasive species
  Over collection

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 habitat 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.

Ecological Role

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.

Life Cycle

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.

Egg Stage

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.

Larval Stage

Firefly Larvae 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 before ingestion.

Pupa Stage

Firefly Pupae 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 red.

Mating and Reproduction

FireflyMating 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 mate.

Firefly Conservation

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.

Firefly Basic Needs

Firefly Bioluminescence Flash  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
 Dark nights

Further Information:

 7 Beneificial Insects
 Climate Change Impacts On Wisconsin
 How Do Earthworms Help Your Garden?
 Soil Biology