When was the last time you saw a firefly? Were fireflies more abundant when you were younger, but maybe now you can’t remember the last time you saw them?
Typically flashing after sunset in late spring and summer months, these ‘jewels of the night’ are around, but many may be at risk! Let’s look at what fireflies need to survive, how they’re tied to the San Antonio River Basin, and how we can help them!
Nature’s Lanterns: Firefly Flashes Explained
Fireflies, or as many people like to call them—lightning bugs—are a family of beetles which are able to bioluminesce (biologically emit light) during at least one stage of their life. Their bioluminescence acts as a warning to predators because they contain a toxin! Over time, it’s thought that this illuminating capability was adapted as a courting ritual to attract a mate, which is what most of us have come to recognize and appreciate them for.
Fireflies generate light through a chemical process that takes place in special cells located in their abdomens. Observation © Misty Keith · some rights reserved
Did you know that some fireflies aren’t able to flash as adults, but rather they can emit light as larvae? Usually, we only notice fireflies as adults, as they alight from the ground in search of a mate, dazzling them (and us!) with their flashy display.
Fireflies spend most of their lives in the larval stage—some of them up to two years! While firefly larvae are beneficial predators of smaller animals like snails, slugs, and the like, they are vulnerable in this stage of their life, especially to environmental conditions.
The larvae of some firefly species (like the one pictured here) and can emit their own light! Observation © Alison Place · some rights reserved
Where do fireflies live in our river basin?
Fireflies depend on habitats that retain enough moisture to prevent them from drying out, provide the right food sources for them, and a healthy environment without pesticides or light pollution. Because their main food sources are not usually found in dry or degraded soils, fireflies need a healthy soil profile, usually including a top layer of detritus. Detritus, like fallen leaves and bark, is nature’s free mulch, cycling nutrients back into the soil while also retaining moisture!
River Authority staff conducted several firefly surveys throughout the San Antonio River Watershed last summer.
Common Eastern Firefly (Photinus Pyralis) has been observed in the San Antonio River Basin. © Mishanook · some rights reserved
While fireflies can be found worldwide and in a variety of habitats, the common theme is that they don’t persist in areas without some source of moisture. There may be roughly 15 species of fireflies that call the San Antonio River Basin home, and their need for moisture means many of them may be found in natural areas near our creeks and rivers! This may be especially true as conditions get drier and hotter, whether that’s a seasonal effect or exacerbated by climate change and lack of natural spaces.
Threats to Fireflies
As development increases and sprawls, threats to fireflies are making it more difficult for fireflies to survive. Light pollution, pesticides, drought, degraded land and habitats are some of the biggest threats to fireflies.
Fireflies can be used as bioindicators because of their sensitivity to light pollution and water quality and availability. Healthy, sustaining populations of fireflies can indicate a healthy ecosystem!
If you’re looking to provide habitat for fireflies where you live and keep their light shining, try these easy but mighty actions!
Plant Native Plants + Leave the Leaves! Native plants are adapted to our climate and weather patterns, and many can survive our cycles of drought and heat, which can give fireflies a place to seek safety and away from dry, over-mowed lawns. Leaving leaves in your yard adds even more space for them to find food and shelter throughout their life cycle.
Not wanting to change your yard? Fireflies tend to prefer climbing up long blades of grass before they alight. Mowing too short or too frequently can harm fireflies that may be resting in the grass, especially in late spring and summer months. Longer grass, like natives Little Bluestem or Texas Cupgrass, also keeps more moisture in the topsoil, meaning potentially less water use and more retention!
Be Dark-Sky Friendly! Light pollution continues to increase, but it’s also a very easy, cost-effective issue to reverse! Dark-sky friendly lights are warm-colored, shielded, and targeted. Learn more about how to promote safe nighttime spaces through DarkSky International.
Avoid Pesticides! Insects like fireflies and their larvae are susceptible to pesticides. Outdoor fogger applications and more traditional liquid sprays can kill beneficial insects which include pollinators and fireflies and disrupt the food web of many other animals like birds, fish, and mammals. Outdoor foggers can also be damaging to human health and contribute to air pollution.
If pesticide use can’t be avoided: always follow the label, apply sparingly, and use targeted liquid (not aerosol or fogger) pesticides that can reduce accidental harm to unintended plants and animals.
Spread Awareness! Look for fireflies in your neighborhood, parks, and local green spaces and share the awe of fireflies and ways to help them!
Fireflies are more than just a magical part of summer nights in the San Antonio River Basin—they’re powerful indicators of a healthy, thriving environment and a reminder of the natural beauty that connects us all! Unfortunately, fireflies and their habitats are increasingly under threat from development, putting their future and the health of our ecosystems at risk. By creating safe, healthy spaces—whether through planting native vegetation, reducing light pollution, or simply letting leaves lie—we’re not only helping fireflies but also strengthening our connection to nature and each other. Together, as a community, we can protect the health of our rivers, parks, and neighborhoods, and ensure that fireflies remain a treasured part of our shared landscape for generations to come.
