In most years, Texas fireflies have largely faded out by August. But this year, a second wave of fireflies has washed across central Texas during mid-September. What’s going on?

Last spring, warm & wet weather conditions produced a bumper crop of emerging adult fireflies (reported here). And similar weather conditions this fall have apparently created a repeat performance (reported here & tweets below).

Sept 2016 sparked a firefly Twitterstorm from Austin

Entomologist Ben Pfeiffer of Firefly.org says Texas typically has two firefly seasons, but this year he’s seen an especially impressive second wave. According to Pfeiffer, the main star has been Big Dipper fireflies, Photinus pyralis, which are easy to recognize by their J-shaped flashes at dusk. But adults of several other firefly species have also made a second appearance (these include Pleotomus pallens, Photinus stellaris and Photinus dimissus).

As I describe in Silent Sparks, a firefy’s life is a journey of astonishing transformation. The luminous adults we so admire are merely the tip of the firefly life cycle. Like all beetles, fireflies go through four distinct life stages –  from egg to larva, through pupa to adult – that look something like this:

Usually a firefly larvae will spend 1-2 years feeding before it becomes an  immobile pupa and then finally emerges a few weeks later in the familiar adult form. So the September adults grew up from lots of carnivorous larvae that were living underground last summer.

The second wave of Photinus pyralis adults look different – they’re a lot smaller than the typical spring adults. And Pfeiffer reports that they flash more erratically,  and seem to light up in response to anything that flashes near them.

Did they grow up fast from eggs laid last spring?  Or are they just late-bloomers? We just don’t know. Surely these Texas fireflies not only provide some welcome late-season wonder, but they also provide a fascinating mystery just waiting to be deciphered by some intrepid firefly biologists.