Summer is coming. Next week (June 21) is the summer solstice, the longest day of the year in the Northern Hemisphere.
The summer solstice is traditionally considered a magical time when spirits and fairies find it easier to cross into our world. And although you probably won’t see any fairies in the next week or two, one creature will soon be lighting up the night: lightning bugs.
Lightning bugs (or fireflies, depending on where you’re from) are not bugs or flies but beetles. Like other beetles, lightning bugs have a pair of hardened wing cases called elytra. When not in flight, the wings are folded underneath the elytra; when they’re flying, the elytra help lightning bugs stay balanced.
There are over 2,000 species of lightning bugs, and you can find them living on every continent except Antarctica. You’ll typically find them in more marshy areas, and some species are actually aquatic during their larval stage. Some lightning bug species can get pretty big: female Lamprigera lightning bugs can grow to be the size of a human palm!
Why make light?
Lightning bugs are named because of their ability to produce light from their bodies. This raises the question: why do they do this?
It all comes down to finding a mate. Male lightning bugs flash to attract females. When the females see a male they like, they’ll flash back. Each lightning bug species has its unique flashing pattern so that individuals from the same species can find each other. Some species even synchronize their flashing, which is thought to help females ensure they respond to a male of their species.
But while lightning bugs are famous for making light as adults, not all species do. For example, lightning bug species in the western United States cannot produce light and use pheromones to find mates instead. Even if not all adults glow, all larvae produce light to warn predators that they don’t taste good!
Energy efficient
Lightning bugs are bioluminescent – all the light they make comes from their own bodies. And it turns out that this reaction is one of the most efficient light reactions in the world. Whereas most reactions give off by-products like heat, the chemical reactions in a lightning bug’s light (photic) organ produce almost 100% light. Compare that to light bulbs – incandescent bulbs emit only 10% of their energy as light, and fluorescent bulbs only emit 90% of their energy as light.
Because it doesn’t give off heat, a lightning bug’s light is called a ‘cold light.’ And it’s a good thing it’s cold – a lightning bug would be roasted alive if its photic organ emitted heat!
How exactly does this light reaction work? It’s pretty simple – light is produced when calcium, adenosine triphosphate (ATP), luciferin, and oxygen combine in the presence of the enzyme luciferase. Lightning bugs can control this reaction by bringing in oxygen to their light organ. Oxygen comes in, and the light goes on. No oxygen, no light. The final key ingredient is uric acid crystals, which are located in cells in the photic organ and help reflect light away from the lightning bug’s body.
A bitter pill
Lightning bugs do not taste good! They reflexively bleed (auto-hemorrhaging) when attacked, even if their bodies haven’t been punctured. This blood contains bitter-tasting chemicals that can be poisonous to some animals (PSA: don’t feed pet reptiles lightning bugs!). Although I couldn’t find a case of a human dying from lightning bug ingestion, you probably wouldn’t find eating them pleasant, and you shouldn’t try it!
But lightning bugs don’t let their own bad taste stop them from eating other insects. Lightning bug larvae are carnivorous and particularly enjoy eating snails. And while most adult lightning bugs eat pollen and nectar, a few species are carnivorous.
These carnivorous lightning bugs are sometimes called femme fatales. Instead of eating other insects, they prey upon other species of lightning bugs. Females in some species in the genus Photuris mimic the light patterns of females of other lightning bug species. This attracts males, who are quickly devoured instead of getting to mate with a female as they expected.
Good for science
Scientists have been finding ways to use luciferase since it was discovered in lightning bugs. For example, it can be used in biological research to detect the level of ATP in a cell, which tells scientists how active the cell is at that time. This can be extremely useful for studying diseases where cells have different activity levels. Luciferase is also used in food safety testing and some forensic tests.
Originally, the only way to collect luciferase was to extract it from lightning bugs. While synthetic luciferase is available today, some companies still harvest lightning bugs; unfortunately, this could contribute to the decline of lightning bug populations. There are fewer and fewer lightning bugs around, with one study finding that 14 out of 128 Lampyridae species face extinction.
Lightning bugs are also vulnerable to human activities like light pollution and habitat destruction. If too much artificial light is present, lightning bugs have trouble using their flashes to find mates. And as we pave over fields where lightning bugs live, the number of suitable habitats for these insects continues to decrease.
If we start protecting the habitats we have left, we can hopefully continue to have lightning bugs lighting up summer nights.
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