Imagine a quiet, romantic, warm summer night. You are relaxing, maybe camping in the countryside. It’s an all-round beautiful evening, the crickets are chirping, the only light for miles is that of the charming fireflies, flying carefree around you and… Oh my God! What is that firefly doing?
You thought fireflies were peaceful little creatures, one of the few bugs you actually liked. You heard that adult individuals of most species don’t even feed. Yet, you see the light of one particularly vibrant individual go out when meeting the light of another. What’s going on? Well, long before Gone Girl came out, nature has had its own femme fatales.
Fireflies have a light-producing enzyme, known as luciferase, which is found within cells of the lantern. Luciferases require oxygen, luciferin and adenosine triphosphate (ATP) to catalyze a chemical reaction that produces bioluminescence in these insects. These master chemists use this process of non-thermal light production to communicate with each other, using their flashes as “skywriting”. The common eastern firefly Photinus pyralis, also known as the big dipper, a name which relates to their mating displays, where males are the first to start the series of patrolling flashes needed to locate and mate with a female. These flashes appear as a fishhook, giving rise to their big dipper reputation. The females, unlike the males, take a sedentary approach, where they respond to the male’s signal through a single flash of their heart-shaped lantern. They will flash every 6 seconds and wait for a responding flash from the female, which comes after a 1-2 second delay. Females only respond to the signals of their conspecific fireflies, as they are able to identify the intensity of the yellow colouration, the temporal patterning and duration of their bioluminescent signals.
Males bear a nuptial gift for their new girlfriends, which contains “lucibufagins”. This steroid makes the fireflies unpalatable to predators. It is thought that it is passed on from mother to offspring, making them less susceptible to predation. Therefore, the glow of their pupae believed to be a form of aposematic signal towards potential nocturnal predators.
This, however, attracts the attention of another female, from another species, one which is unable to produce her own toxic chemicals, but has found a way to exploit those of others. The Photuris female imitates the signals normally emitted from female Photinus pyralis, a strategy known as aggressive mimicry. This attracts the male right into her trap, where she attacks him, causing the lucibufagins to come out as tiny droplets. Then she devours him. The toxins provide her with protection against predators like jumping spiders. Females with lower lucibufagins measured when they reflex bleed have been demonstrated to be preferred by jumping spiders compared to their counterparts with high lucibufagins. In other words, it’s not their fault, it is natural selection forcing them to be cruel so that they do not end up as a meal themselves.
The big dipper males, however, are striking back. They spend longer looking for their female mates in an attempt to avoid false signals and try to quickly escape femme fatales, when they do become fooled and answer to their signals. Additionally, they fight their opponents through the weapons these dangerous females seek – masterful chemistry. Some males are now producing a sticky substance sealing the mouthparts of their opponents shut, allowing them to escape whole.
Either way there is one thing both of these species can agree on, life as a firefly is tough and there are many things to be afraid of in the dark. The twinkling lights that bring you so much joy and optimism may be living their own sad, twisted lives without us even noticing.