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www.thevillagenews.co.za
7 October 2020
MY ENVIRONMENT
The magical world of fireflies By Dr Anina Lee
O
ctober brings firefly magic. No matter how often you have seen their fairy lights, they never fail to delight. It is now the fourth year that I plan to go and see them and to take with me anyone who would like to share the spectacle and learn more about the lives of fireflies.
In The Village NEWS editions of 16 and 23 October 2019 I wrote about the life cycle of these little beetles and explained what bioluminescence is and how fireflies control their light flashes. (These articles are also on the Whale Coast Conservation website under CHAT.) Flashiness vs substance Fireflies are the flashy stars of the insect world. At night, each little beetle shines like a lamp – and, appropriately, they belong to the family Lampyridae. The ‘lamplight’ of fireflies is a cold light, produced by a biochemical reaction. Fireflies produce light in special organs in their abdomens. They do this by combining four elements: chemicals called luciferins, enzymes called luciferases, oxygen and the fuel for cellular work, ATP. Fireflies control their flashing by regulating how much oxygen goes to their light-producing organs – which, in turn, depends on the production of nitric oxide, the same chemical produced by Viagra. Spring heralds romance for these magical insects. While courting on-the-wing, male fireflies attract females' attention with their bioluminescent flashes. If a female is impressed by the initial flashiness, she will flash in reply. Now here's an interesting thing. Research by biologists at Tufts University reveals that, after the lights go out, female fireflies prefer substance over flash. They seem to choose mates able to give them the largest ‘nuptial gift’ called a 'spermatophore'. This is a high-protein sperm package that helps them to produce more
eggs. But the next night these females are likely to mate again with a different male. And males will mate with other females. After a female has mated with several males, the big evolutionary question becomes: which male gets to pass along his genes to the next generation of firefly babies? How much of a male's success – in both mating and fathering offspring – depends on his flashes or on his nuptial gift offering? Not unlike human romance, love remains a mystery among fireflies, and first impressions are only part of the story. While a female's initial assessment of potential mates is based on males' luminescent flashes, the Tufts research shows that once a pair makes contact, sexy flashes no longer matter. Instead, it's those males that have larger nuptial gifts to give that win out with higher reproductive success as their gifts contain more sperm. At this point, the females have little regard for flashiness. Males with limited resources may face a tradeoff between investing either in sexy flashes or in costly gifts. The darker side of romance This all sounds very romantic and beautiful. But there's a dark secret: some female fireflies dupe the males of another species with false flash patterns – then, when their amorous would-be partners approach, they attack and eat them. The femme fatales aren't doing this from malice or hunger: they're trying to ingest a toxin that will keep them safe from predators.
agriculture to feed the growing world population. With increased agriculture comes the increased use of insecticides designed to kill insects, including fireflies. The use of snail and slug bait destroys the firefly larvae's main prey species. Firefly larvae can remain in the soil for up to two years, so they require undisturbed habitat under leaf litter, and an ample supply of all things slimy, like worms, snails and slugs. Yes, their prey is much larger than they are themselves. They have a vicious bite, then inject digestive enzymes into the victim, and suck up the resultant 'smoothie'. With humans comes artificial light at night. Firefly mating rituals depend on their light display, and artificial light, primarily bright white LED lights, interfere with their mating rituals. Even a smallish town like Hermanus produces significant 'night glow'. One of my best firefly experiences was during an evening of load shedding. When the lights went out, the stars suddenly appeared twice as bright and the fireflies sparkled like jewels in the pitch dark. What a memorable sight! Join one of Whale Coast Conservation's firefly walks. Contact anina.wcc@gmail.com for more information. For an excellent tutorial on fireflies and a video go to https://www.thesouthafrican.com/lifestyle/great-smoky-mountains-firefly-event/ or click the play button on the right.
As the saying goes, "You are what you eat." In this case, a Photuris female eats a Photinus male to get chemical defences that are present in his blood. The toxins deter predators like birds, spiders, ants and others. These potent toxins are steroids similar to the heart poison generated from the foxglove plant, Digitalis. Fireflies under threat Sadly, firefly species, just like most other insects, are under threat. These days it's unusual to see them ‘at the bottom of the garden’. Habitat loss, pesticide use and, surprisingly, artificial light are the three most serious threats endangering fireflies across the globe, raising the spectre of extinction for certain species and related impacts on biodiversity and ecotourism. As the human population grows across the world, more and more firefly habitats are consumed by urban spread and land cleared for
TOP & ABOVE: Fireflies are the flashy stars of the insect world. At night, each little beetle shines like a lamp – and, appropriately, they belong to the family Lampyridae. PHOTOS: fireflyexperience.org CIRCLE: Spring heralds romance for these magical insects. While courting on-the-wing, male fireflies attract females' attention with their bioluminescent flashes. If a female is impressed by the initial flashiness, she will flash in reply. PHOTO: Radim Schreiber
