By Ashley Kulhanek and Eric Barrett
Last summer, a neighbor asked why we don’t see lightning bugs anymore. This summer, there are already posts on social media asking about the lightning bugs and fireflies.
Each of these concerns were about the lack of our beloved lightning bugs. Last year, we ended up with beautiful displays, and there is no reason to think they’re gone this year.
Neither true bugs nor flies, these beetles in the family lampyridae are a summertime favorite. Even the most squeamish among us must admit awe and fascination over these beetles with glowing butts. And while they, like many insects, experience pressures from human impacts and habitat loss, we think this year, firefly lovers are just wishing for them to come out earlier than they are ready to for this season.
Let’s start there first. Yes, we will see lightning bugs this year. The reality is the impact of cooler weather likely slowed things down. As beetles, their lifecycle involves an egg, larva, pupa and adult emergence.
Eggs are laid in moist humus, leaf litter or moist soil. Upon hatching, many Ohio species will spend two or more years as predatory larva in the soil eating snails, slugs, worms and other smaller soil arthropods like springtails.
They then pupate and emerge as adults to feed, mate and lay eggs. And waiting for those adults to emerge is what we’re doing now.
There are many different species of lightning bugs that will develop at different rates. But we have some examples to go by to help us time their appearance using Growing Degree Days.
GDD’s are a measure of heat accumulation across the season that correlate with the growth and development of plants and insects during the growing season and are a good indicator of predicting insect emergence.
For our lightning bugs, for example, one source has cited adults emerging around 950 Growing Degree Days on average.
Another study cited that “a good display” time is around 990 GDD on average and peak display would be later, around 1094 GDD.
In the Youngstown area, we are still below the growing degree days (GDD) on average required for peak emergence at only 722 GDD, June 14.
By comparison, in 2022 Youngstown’s GDD was 926, a fair bit closer to peak display. So, a continued warm up period should get those lightning bugs a-glowing soon in the next weeks or so, and we can enjoy their light show again.
In northern Medina County, we just hit 955 and we may hope to see shining bottoms glowing with the next weeks of warm dusky evenings. And another example, in 2017, Joe Boggs, in the Cincinnati area, didn’t see his first firefly until June 22 according to a past BYGL post. So don’t despair just yet.
Second, dry weather could impact fireflies. Many firefly species are aquatic or semi-aquatic favoring moist habitat along streams, transition zones between forests and fields, taller grass and humid areas. So, The increased moisture from recent rains may help build those favored habitats as GDDs continue to increase toward their emergence.
Third, insects often go through cycles of booms and busts. Population cycles of insects can be affected by winter temperatures, moisture, humidity, predator populations, diseases and more. While this occurs naturally through predator-prey cycles, available food, weather, etc.
There are external threats to fireflies, too. We cannot ignore that human impacts have seen a decline in insect populations overall, and those factors threaten lightning bugs as well.
Habitat degradation and loss from humans is a major concern for fireflies and other insects.
But also light pollution and the use of pesticides are other factors like climate change are cited (Lewis et al, 2020).
A 1965 study by D.E. Marvin documented 31 species of firefly in Ohio. Now we claim about 2 dozen.
On i-Naturalist, (a crowd-source site where naturalists and outdoor photographers can document observations worldwide) only 21 species have been reported by citizen scientists in Ohio.
So how can we help? In your own yard, consider mowing higher this time of year to improve habitat (and also to save the blades from being scalped after being so parched).
Leave leaf mulch or use wood mulch around plants to mimic the humus layer where eggs may be laid and to conserve moisture. Just make sure to mulch appropriately. A good rule of thumb is 2 inches deep with a donut of space left around trunks and stems of shrubs and trees. No volcano mulch here.
Reducing pesticide use and/or proper, safe pesticide use is always advisable and helpful to all insect species.
We can also preserve waterways and aquatic habitats that lightning bugs will favor.
Reducing outdoor lighting also helps them to show off their lights and find each other to mate and produce the next successful generation of our favorite summertime light show.
So, be on the lookout for fireflies, and do what you can to help keep them a summertime favorite for generations to come.
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