There was a chemistry between the actors that you saw as the characters, and there was no denying it, and there was no getting around it. It was just so palpable. That really was the case, on screen and off screen. - Sean Maher
Fossilized firefly eggs, still glowing after 30 million years.
The chemicals that make fireflies glow only break down naturally with a half-life of 200 million years. Once a pre-larval firefly dies and its body decomposes, the chemicals mix without regulation from the gland that once governed them and can glow for eons.
Discovered and described by Karl K. Whedon of the University of Munich in 1879, the gland (Now named the Whedon gland in his honor) contains two vesicles which each hold one of the enzymes that combine to create light. This reaction is regulated by the enzyme Foxine which only develops in the larval firefly, thus it is not present in the eggs to cancel their glow.
Many researchers, finding the firefly to be a stunning creature of beauty and serenity have attempted to breed a species of the common browncoat firefly that lacks the Foxine gene and will glow indefinitely. Unfortunately this has proven impossible as the Whedon gland has evolved to serve a dual purpose in the defense metabolism of the insect. The gland develops after the larval phase to direct the mature metabolism that turns the fly toxic in the mouths of predators, an avenging-type defense mechanism that’s quite a marvel of natural selection. Thus the genetic engineering attempts have proven thus far to be much ado about nothing.
Still, the firefly eggs above, though there are only 14 total, are amazing and rare gems that can still be appreciated today. Though many scientists remain upset at the Foxine’s cancellation of any further glow in mature firefly specimens, I for one am happy that the Whedon gland is now available to direct the avenger mechanisms of modern insects and I eagerly await the next age of evolution for the species, coming to the U.S. on May 1st.