How to Keep Fireflies Alive. While the best way to admire the warm glow of fireflies is in their natural habitat, you may wish to catch a few, keep them alive in a jar and observe them up close. Remember, though, that these members of the lampyridae family were not meant to exist in captivity. If you capture them, enjoy their glow for a night or two. Then, release them back into a damp, vegetated area.
Select a large glass or plastic jar to catch your fireflies. Do not poke air holes in the jar lid, as it will cause the atmosphere to dry out too quickly. Humidity is critical to keeping fireflies alive, and the oxygen that remains in a sealed jar is enough for them to live on for a short time.
Line the bottom of your jar with grass to make your fireflies feel at home. Fireflies are typically found around meadows or wooded areas and enjoy hiding in cool grass and bushes during the day.
Drop a fresh apple slice or a piece of damp paper towel into your jar to maintain the jar's humidity level. To keep the fireflies alive for a few days, add a new apple slice or paper towel each day.
Capture several insects in your jar, and screw the lid on gently without overtightening.
Allow the jar to get natural light during the day, but make sure you do not place it directly in the sun. Direct sunlight will heat the jar too much and could kill the fireflies.
Release your fireflies into their natural habitat in the evening, and enjoy watching them blink their way across the night sky.
TL;DR (Too Long; Didn't Read)
Observe the blinking pattern of your fireflies. There are more than 100 firefly species in North America, and each one has its own blinking code. You may have captured several species in one jar. Check out BackyardNature.net for more details on these glowing insects (see Resources below). If the glow of fireflies relaxes you or takes you back to your childhood, consider purchasing an electronic version for your backyard. FireflyMagic.com sells solar, battery and electric-powered firefly replicas with tiny microchips that allow them to blink and fade (see Resources below).
Do not try to keep your fireflies as pets. Given their short lifespan, it is difficult to keep them alive in a confined area for more than a few days.