Last time we had a rather technical discussion about the biology and chemical mechanics of fireflies. I appreciate all of the comments, and some of them indicated that I should expound a bit.
Most of the comments were concerned with firefly ecology and how to encourage their numbers. It is true that fireflies seem to be on the decrease insofar as populations go, and there are several reasons for that.
One reason that I am pretty much sure DOES NOT deplete the population is live capture, with or without release. I have a call in to Sigma-Aldrich to see if they still buy fireflies. If so, they are supplying lots of material for research whilst doing little harm to the population.
It is HARD to catch enough fireflies to damage the population! As I get more information about the bounty, if any, on members of the Photinus genus, I shall share.
First of all, the US species of Photinus do not eat after becoming adults. They are doomed to die within a week or so after becoming sexually mature. Perhaps that might be a better fate for humans as well, since heartbreak would be very much shortened.
Other genus of fireflies DO have predatory tendencies, but Photinus species just live off of the captured nutrition in their larval stage and never eat again. That is why capturing them to sell to research companies does little if any harm. Besides, most of the flying fireflies are males, so by catching them the egg laying females are fairly well protected.
What causes them harm is habitat destruction. This comes in many forms, mostly because of us humans taking over their territories. Fireflies need several things in order to survive the larval stage, mostly shelter and water. Most firefly larvae develop in downed wood, where their prey can be found in the form of small insects, other larvae, and small slugs. They particularly take to edges of ponds and slow moving streams where both prey and water are available in large quantity.
You can encourage firefly populations in your yard by doing some untidy things. First, let some of the grass around your fence to grow rather than trimming it. Both larvae and adults like the cover that tall grass provides. Instead of trashing fallen tree limbs, find a place to stack them and let them rot in place. Providing sources of water is a bit trickier because of mosquitoes, but if you pour out the water and replace it every couple of days that will not be a problem.
I live in a suburban setting the the Bluegrass of east central Kentucky, and in the seven springs that I have seen here there have been abundances of fireflies. Behind the houses across the street is quite a bit of acreage of open field, and behind the houses on my side of the street is the same. This goes a long way to keep the population healthy. There are a couple of ponds across the street as well.
Light pollution is another cause of reductions in firefly populations in the opinion of many. That makes sense, because as we discussed last week they use light to find mates. In my neighborhood there are no street lights (except for one neighbor who pays to have two for security reasons), so fireflies can communicate as nature intended. You can encourage firefly populations by turning off outside lights during the season that they are mating.
Indiscriminate use of pesticides may be a factor in population reduction. Perhaps the most harmful practice is the broadcast spraying for mosquito control that is done in many areas. Such spraying kills not only mosquitoes, but other insects as well, including fireflies. The eggs are somewhat protected since the female lays them just underground for the most part, so public awareness to put pressure on municipalities not to spray during mating season is a good idea. Likewise, those who garden should use the minimum amount of pesticide to protect garden plants.
Unfortunately for fireflies, they prefer the same habitats that mosquitoes prefer. In my part of the country, the county does not spray for mosquito control, at least where I live. When they get bad and I must be outside, I use repellant and mosquitoes do not bother me. By the way, I detest DEET, the active ingredient in most repellants. However, there is a repellant that is not oily, will not harm plastics, and is just about as effective as DEET. It is called picaridin (or icaridin). Both OFF! brand and REPEL brand carry picaridin preparations, and I can tell you from experience that it works well (you might have to apply it a little more often than DEET based preparations) and is not unpleasant like DEET is.
Here are the structural formulae for both:
Picaridin (1-piperidinecarboxylic acid 2-(2-hydroxyethyl)-1-methylpropylester)
As I was rooting around for information for this piece I found how fireflies modulate their flashes. It is a rather complex mechanism, but it does involve the supply of oxygen to the activated complex mentioned last week. It turns out that the firefly can, by control by its nervous system, divert oxygen to mitochondria to produce ATP (regenerating it from the production of the activated complex). When the firefly "decides" to flash, it releases the neurotransmitter octopamine. This in turn triggers the enzyme nitric oxide synthase to release nitric oxide. The release of nitric oxide inhibits the mitochondria from using oxygen, making oxygen from respiration available to oxidize the activated complex, thus causing flashing. Here is a structural formula for octopamine:
Note that it is structurally similar to the human neurotransmitter norepinephrine:
What is interesting is that nitric oxide (NO) is the same mediator that is increased in concentration when the drugs used for erectile dysfunction are taken by human males. Nitric oxide is indeed a love potion for both man and beast!
Here is link to a really cool .mov motion picture of fireflies being placed into a container with artificially enhanced NO levels. This file is around 82 MB, so expect to wait a while before you watch. You have to have Quicktime to view it. Pretty cool!
Here is another video about energy costs and predation costs for flashing. It is short but interesting:
All in all, fireflies are really cool little buggers that provide lots of entertainment, especially for little ones and those who love the little ones. The squeals of joy when a child catches yet another firefly and puts it in the jar are sounds that just have no match anywhere. I hope to be able to participate in that tonight, so if I am late for Comment Time you know why. I WILL show up for Comment Time, I think. It all depends.
Well, you have done it again! You have wasted many more einsteins of perfectly good photons reading this piece about photon producing beetles. And even though the Fox "News" Channel realizes that they are being hyperbolic about the "leak problem" when then read me say it, I always learn much more than I could possibly hope to teach by writing this series, so keep those comments, questions, corrections, and other feedback coming! Tips and recs are also always welcome.
As I said, I shall be here for Comment Time (although maybe late) and shall stay as long as comments warrant. Tomorrow evening I expect to be back for Review Time at 9:00 Eastern.
Doc, aka Dr. David W. Smith