The Fireflies of Andorra Meadow

Conservation // June 23, 2022

Have you ever seen the fireflies in Andorra Meadow?

Perhaps Philadelphia’s best kept secret resides in an overgrown field on the extreme north western county boundary. At around 8:20 or thereabouts, every June evening, the local residents slowly rise out of the tall grasses and milkweeds. You’ll notice their slow swerving and golden trails. By about 8:45, they begin to rise above, hastily crossing each other. By about 9:15, they’ve begun their transition to the trees. At this point, you’ll notice a faint synchronization in some blinks, but not a majority of blinks. The field lights up with yellow, crimson, and sea-green flashes from the grass to the tops of trees.

Strolling through Andorra Meadow during firefly season remains one of the most enchanting walks one can take in Philadelphia, if not all of southeastern Pennsylvania. I first became aware of our firefly community when, then Friends of the Wissahickon assistant, Varian Bosch, took our Crew Leader class on a brilliant firefly hike through Andorra Meadow. I gazed in amazement. I couldn’t believe the show.

Perhaps nothing exemplifies a nocturnal species better than fireflies, surging at dusk and continuing through the evening hours. With careful attention to detail, you’ll astutely notice some fireflies hovering swerving in a repetitive “J” maneuver. Others simply blink. Females often graze close to the ground while the males fly up high.

In recent years, I hear friends tell me how they used to see so many fireflies as kids but now hardly see any. This phenomenon isn’t strictly confined to city dwellers. For certain, we make life hard for fireflies. Keeping grass mowed at putting green height. Pesticides. And there lurks an even more insidious hazard that we project onto our environment for which no one even appears to be aware of.

Artificial light at night (also known as ALAN) does a lot to subdue the nighttime ambience by replacing it with daytime brightness. In fact, with the rise of LEDs, places like Philadelphia, even eliminated any warm colors from streetscapes by switching sodium vapor fixtures over to the controversial 4000K temperature lighting (for reference 5000K is the color the sun emits).

Lighting certainly makes it easier to walk at night. It helps provide traffic safety in intersections at night. It also completely reshapes nighttime ecology.

Specifically, with regards to lightning bugs, artificial light impedes on vital mating communication, casting visual interference over a female’s glow. In other species, such as Monarch butterflies, lighting confuses and exhausts the animal into believing it’s still daytime, thereby rendering its journey all the more precarious. According to the Audubon Society, the impacts of light at night on birds has been well documented for a hundred years, of which, only after major bird kills have we begun to participate in safety programs, such as ‘Lights Out Philly.’

What can you do to make your property firefly friendly?

Keep your grass a few inches higher than is deemed conventional. Mowing your grass like a golf course green does no one good – not the grass, not the creatures living there, and encourages runoff issues as ground fertilizer quickly exits your greenspace for the cozy confines of our drinking supply.

Next, try limiting your use of pesticides and herbicides. Fireflies don’t start out as fireflies, they start life as a larva, concealed on or under the ground. Even when used in a targeted manner, the poisons can still carry to unintended insects.

Finally, light trespass can occur when unshielded lights illuminate unintended areas. Lights that emit the most light trespass typically have visible light sources. Instead, install and use only top down, shielded lighting. Only turn on your external lights when you need them, do not leave them on all night. And use motion sensor lighting in place of any security lights you may have up.

The key with the lighting is to not have a steady wasted stream of light across the grassy area. If we left our sinks running water the way we leave our exterior lighting on, our rivers would run dry in days.

Consider this, on average, we only spend anywhere from one to three hours outside daily. Yet we light up our driveways, front of our houses, sides of our houses, and even our trees all night long. While that may have some visual appeal, it greatly impacts nocturnal ecologies who have to live in the environment you decided to light up all night. Increasingly, there’s simply no refuge for the nocturnal environment.

In addition to these steps, plant native trees (especially pines) where possible (see this link for some additional ideas). The fireflies will thank you by putting on an awesome show.

-FOW Crew Leader, Bill McGeeney