My foray into firefly ecology over the past week has been fascinating on a number of levels- clearly in my previous ideas about fireflies, I had far too simple a concept of what these insects were: fireflies are more diverse, more widespread, and more sophisticated than I had ever imagined. They are also more indicative of environmental conditions. Although I was thinking too narrowly about what it means to be a firefly, unfortunately I was not missing the big picture when it comes to concerns over firefly conservation- populations are declining worldwide for a number of reasons.
What does it mean to be a firefly? As it turns out, it doesn’t necessarily mean that you turn into a flying, glowing insect. While all firefly larvae are bioluminescent, not all adults are (Smith 2009)- witness Pyropyga nigricans which is found throughout North America, is active during the day, and uses pheromones rather than light to attract mates (Lloyd 1999) (and after I saw pictures of this species which ranges throughout New England, I wondered how many times I had brushed this beetle off me with a lack of respect because I didn’t know what it was). The firefly’s glow is caused by chemical reactions involving the enzyme luciferase, and production of nitrous oxide appears to act like a lightswitch and give the insect control over light production (Lewis & Cratsley 2008). Some firefly larvae go through an aquatic stage (such as Luciola ficta in Taiwan) while others (like Photuris pennsylvanica in eastern North America) inhabit soil. For those fireflies that do flash, in some parts of southeast Asia, males gather together in trees for synchronized flashing, which I think must be an amazing sight (and I did read a discussion of whether some species in North America do this as well- see Milius 1999). What are the common denominators? As I said before, all larvae are bioluminescent. And firefly larvae are predaceous- depending on where they are, they eat snails, slugs, earthworms, and other soft-bodied insects (Keiper & Solomon 1972, Ho et al. 2010). People all over the world are fascinated by fireflies (a large amount of the research I found was centered around how the light is produced, what types of signals are used, and how we can use luciferase in areas such as medicine- it seems to me that we are putting a lot of effort into understanding how fireflies do what they do, and not so much into whether they will be able to continue doing it in the future). Fireflies, wherever they are, also have the capacity to act as ecological barometers because their life-cycles are dependent on water, soil, and atmospheric health.
What ecological threats do fireflies face? In some ways, fireflies face the same issues that are causing problems for species around the globe: habitat loss and pollution (not exactly new or glamorous, right?)- but there are also a few twists to this story. When we think of habitat loss, we tend to think of forests being cut down, swamps being drained, and grassland being developed, and those types of changes are important for firefly conservation, but there are also smaller disturbances that are causing big problems. For species with aquatic larval stages, being able to disperse through water systems and move between water and soil is crucial- consequently, changes in water flow and stream access can prevent larvae from evading predators and finding prey, and changes to the form of irrigation ditches, such as cementing, trap larvae on one side of the barrier (many species in Japan, for example, have declined in part because of cement in irrigation ditches- see Koji et al. 2012). Efforts to control Phragmites reeds (you remember them from the invasive aquatics discussion, right?) through burning may be partially responsible for the decline in Photuris salina populations in Delaware (Heckscher 2010). And we need to expand how we think about pollution as well. For species with aquatic larval stages, water pollution is a big problem (Heckscher 2010, Koji et al. 2012)- and remember that terrestrial species can be injured by water pollution because their prey is often impacted by water quality. Fireflies can also be killed by sprayed pesticides, especially since many of these species tend to spend their time near water (which can harbor mosquitoes) and fields (which may contain harvestable crops). In addition to these more commonly-discussed types of pollution, fireflies also have to contend with light pollution- at least since the first half of the 20th century, we’ve known that bright lights can interrupt firefly behavior and prevent flashing displays (Buck 1937). Many researchers today see a relationship between declining global firefly populations and the spread of artificial light into more and more natural habitat (Thancharoen et al. 2008)- if fireflies don’t flash or can’t see response flashes because of light pollution, populations in human-altered landscapes are going to be in trouble.
So there is more to fireflies and firefly conservation than I had originally suspected, and I’m sure that I haven’t even scratched the surface yet. Hopefully this post gives you a sense of firefly ecology and the larger threats facing populations around the world- for my next post, I’ll look into what research says about what might work (or not) to counter these threats.
Works cited:
Buck, JB. 1937. Studies of the firefly. I. The effects of light and other agents on flashing in Photinus pyralis, with special reference to periodicity and diurnal rhythm. Physiological Zoology 10: 45-58.
Heckscher, CM. 2010. Delaware Photuris fireflies (Coleoptera: Lampyridae): new state records, conservation status, and habitat associations. Entomological News 121: 498-505.
Ho, J-Z, Chiang, P-H, Wu, C-H, and P-S Yang. 2010. Life cycle of the aquatic firefly Luciola ficta (Coleoptera: Lampyridae). Journal of Asia-Pacific Entomology 13: 189-196.
Keiper, RR & LM Solomon. 1972. Ecology and yearly cycle of the firefly Photuris pennsylvanica (Coleoptera: Lampyridae). Journal of the New York Entomological Society 80: 43-47.
Koji, S, Nakamura, A, and K Nakamura. 2012. Demography of the Heike firefly Luciola lateralis (Coleoptera: Lampyridae), a representative species of Japan’s traditional agricultural landscape. Journal of Insect Conservation 16: 819-827.
Lewis, SM & CK Cratsley. 2008. Flash signal evolution, mate choice, and predation in fireflies. Annual Review of Entomology 53: 293-321.
Lloyd, JE. 1999. On research and entomological education III: firefly brachyptery and wing “polymorphism” at Pitkin Marsh and watery retreats near summer camps (Coleoptera: Lampyridae; Pyropyga). Florida Entomologist 82: 165-179.
Milius, S. 1999.U.S. fireflies flashing in unison. Science News 155: 168-170.
Smith, BW. 2009. Firefly diversity in Columbia: patterns across a dynamic landscape. Master’s thesis, University of Florida.
Thancharoen, A, Branham, MA, and JE Lloyd. 2008. Building twilight “light sensors” to study the effects of light pollution on fireflies. The American Biology Teacher February: 6-12.