Fireflies of Iowa
Summer nights in Iowa are not complete without the tell-tale bob and weave of floating lights across fields, woodlands, and yards. More commonly referred to as fireflies or lightning bugs, these bioluminescent wonders are actually beetles in the Lampyridae family. The name Lampyridae comes from Greek roots meaning “to shine.”
Fireflies can be found in both temperate and tropical regions all over the world, with nearly 2,000 species identified from every continent except Antarctica. More than 120 species occur in the contiguous United States and Canada.
Iowa is home to an estimated seven to thirteen species of fireflies. Although some species do not glow and are active during the day, the majority are the classic flashing nocturnal beetles we see at night.
Fireflies native to Iowa are generally categorized into two groups: flashing (nocturnal) fireflies and non-flashing (diurnal) fireflies.
Flashing (Nocturnal) Fireflies
The following species are responsible for Iowa's spring and summer light shows. Because they look similar to the naked eye, scientists often have to rely on flash pattern, flash color, and flight height to tell nocturnal species apart.
Non-Flashing (Diurnal) Fireflies
Some of Iowa’s native fireflies do not flash as adults and are active during the daytime. Because they cannot use light to find each other, they use pheromones instead.
Science of the Glow
The Why
While not all fireflies glow, those that do aren't just doing it for aesthetic appeal. Their flashes are a sophisticated form of communication.
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Finding a Mate: Each species has its own unique flashing pattern (like a secret Morse code). Usually, the males fly around flashing, and the females sit in the grass or on leaves and flash back if they like what they see.
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A Warning Signal: The light also serves as a "stay away" sign to predators. Fireflies contain defensive chemicals called lucibufagins, which are unpalatable and can be toxic to birds and lizards.
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Setting a Trap: Females in the genus Photuris use their lights to lure in males from other species so that they can eat them.
The How
Fireflies produce light through a chemical reaction in the lower part of their abdomen. This process is incredibly efficient; nearly 100% of the energy is emitted as light. For comparison, an incandescent light bulb emits only about 10% of its energy as light, with the rest lost as heat.
The reaction involves three main components:
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Luciferin: A light-emitting biological pigment.
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Luciferase: An enzyme that triggers the reaction.
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Oxygen: When oxygen combines with luciferin in the presence of luciferase, it produces a photon.
Firefly Life Cycle
Fireflies spend most of their lives in the larval stage, often living in soil or mulch for up to two years. Firefly larvae can also be bioluminescent, which is why they are often called "glowworms."
Declining Numbers
If you have noticed fewer fireflies than you remember from childhood, that is not a coincidence. Fireflies across Iowa face three major threats:
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Habitat Loss: Most fireflies need moist, undisturbed ground to live and breed.
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Light Pollution: Artificial lights impede their ability to detect each other’s signals, disrupting their mating.
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Pesticide Use: Chemicals in lawns and gardens can kill both the fireflies and the snails and slugs they eat as larvae.
How Iowans Can Help
The best ways to improve firefly habitat in Iowa:
1. Kill the Lights: Light pollution is like static on a radio for fireflies—it drowns out their signals. Turn off porch lights and motion sensors during June and July. Close your curtains at night so indoor light doesn’t spill into the yard. If you must have light, use red bulbs or low-to-the-ground path lights; fireflies are less sensitive to the red end of the spectrum.
2. Leave the Leaves: Firefly larvae (glowworms) live in the duff—the damp layer of decomposing leaves and organic matter on the soil surface. Instead of raking your lawn perfectly clean in the fall, leave leaf litter under trees or in garden beds. This provides a home for their favorite snacks: snails, slugs, and worms. Without a healthy layer of leaf litter and soil for these critters to live in, the firefly larvae will starve.
3. Plant Iowa Natives: Fireflies need tall perches to signal from and launch into flight. Native Iowa plants provide the best structure. Native grasses like switchgrass, Indiangrass, or big bluestem provide the perfect vertical height for males to take flight and females to hide. Trees like oaks or hackberries provide the deep shade and moisture that keep the ground from drying out. Flowers like aster, goldenrod, and Joe-Pye weed create a dense canopy that holds moisture near the ground.
4. Mow High and Less Often: Fireflies spend their days resting in tall grass to avoid drying out in the sun. Set your mower blade to at least 3.5 to 4 inches. If you have the space, designate a "no-mow zone" or a "micro-prairie" in part of your yard.
5. Create a Damp Spot: Fireflies love moisture. Iowa's humid summers are great, but a dry spell can kill off larvae. If you have a low spot in your yard that stays wet, don't drain it—turn it into a rain garden. Even a small water feature or a consistently mulched, shady corner will help maintain the humidity they need.
6. Avoid Using Lawn Chemicals: Broad-spectrum pesticides are devastating to fireflies. Lawn fertilizers can dry out the soft bodies of larvae and their prey. Mosquito sprays commonly use pyrethroids, which are non-selective, meaning they kill fireflies just as easily as mosquitoes. Slug pellets kill the slugs, which remove the firefly larvae’s primary food source.
7. Get Involved: The Xerces Society, working in collaboration with several other environmental groups, launched an initiative in recent years to better understand and conserve the diversity of fireflies in North America. Citizen scientists can help conduct surveys for species of conservation concern, submit their data via an online portal, and learn more about fireflies and their conservation needs. See Firefly Atlas for more information.
Works Cited
Fallon, Candace, et al. "Conserving the Jewels of the Night." Xerces Society, 2019, xerces.org/sites/default/files/publications/19-049_01_Firefly%20guidelines_web_1.pdf.
---. "Evaluating Firefly Extinction Risk: Initial Red List Assessments for North America." 17 Nov. 2021, journals.plos.org/plosone/article?id=10.1371/journal.pone.0259379.
"Fireflies (Lampyridae)." Insects of Iowa, www.insectsofiowa.org/taxon/lampyridae#:~:text=Fireflies%20(Lampyridae)%20%2D%20Insects%20of,Photinus.
Firefly Atlas, 2026, www.fireflyatlas.org/.
"Firefly Conservation." Xerces Society, 2026, www.xerces.org/endangered-species-conservation/firefly-conservation#:~:text=Other%20species%E2%80%94our%20%E2%80%9Cdark%20fireflies,from%20every%20continent%20except%20Antarctica.
Lewis, Sara, et al. "Illuminating Firefly Diversity: Trends, Threats and Conservation Strategies." MDPI, 19 Jan. 2024, www.mdpi.com/2075-4450/15/1/71.
Wang, Yi-zhe, et al. "Physiological Responses of the Firefly Pyrocoelia Analis (Coleoptera: Lampyridae) to an Environmental Residue From Chemical Pesticide Imidacloprid." Frontiers, 14 June 2022, www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.879216/full.