Fireflies Light Up an Evening at Cylburn

Fireflies Light Up an Evening at Cylburn

During late May, June and July fireflies put on a magical show flashing their little lights in our yards, parks and countryside. Although they are not as prevalent as in years past, they are still one of summer’s pleasures. The “lightning bug” is actually not a fly but a winged beetle. Of some 120 species found in Eastern United States, about 8 to 10 species are resident at Cylburn. Recently we learned more about these fascinating beetles from Dr. Abner Lall, who guided us on a walk around the grounds. He also generously contributed this post if you’re curious about this magical insect. Thank you Dr. Lall for the information and the tour.


Light production in fireflies is due to a type of chemical reaction called bioluminescence. Fireflies utilize bioluminescence as a signal for mating. The flashing males patrol the habitat for responsive females who are perched on a blade of grass or a leaf. When a female is ready to mate, she then answers the courting male with a single short flash.

Since different species of fireflies are active at the same time in the same habitat, the fireflies have evolved a species-specific flash code analogous to a telegraphic code. The flash code consists of three elements: (1) the frequency of flashing of the male, (2) the duration of the male’s flash, and (c) the time delay of the female’s answering flash.

When the flash duration is long, i.e., about 1/2 sec or longer, then the shape of the flash also varies such as in the most common big dipper, Photinus pyralis. Here the males emit a series of ½ sec J-shaped flash every 4.5 sec, and the species females respond with 1.5 – 2 sec delay. Photinus scintillans males emit 0.15 sec duration flashes every 2.6 sec, and the wingless female answers from the grass below with a 0.42 sec delay.

Fireflies2To ensure that all females are well provided with courting males, the ratio of flying and flashing males to quietly perched females on the vegetation is about 50 to 1. So most of the males, in their short life of a week or ten days, never find a mate and die flashing. The females live for a longer period, two to three weeks and lay eggs and die.

The bioluminescent signal is of low intensity and is effective only in light-limiting conditions. Most firefly species are nocturnal. Green is the “default” color of visual sensitivity among insects and the nocturnal species emit lime-green colored light.  In the northern latitudes, twilight zone is extended in duration. The firefly species that have invaded this zone emit yellow to orange light, a signal of contrast color (e. g., yellow butter-cup flower in green grass) against the green-foliage reflected sunlight at dusk. At twilight Photinus pyralis and scintillans emit bright yellow and amber colored lights respectively, while Photuris species emit lime-green light at night.

The number of fireflies has been declining dramatically during the last forty years for several reasons. (1) A reduction in undisturbed habitat availability induced by a dramatic increase in human dominated landscape and highway construction. (2) In northern latitudes it takes two years for fireflies to complete their 8 developmental stages from egg to adult. The larvae are very vulnerable to fertilizers, pesticides and chemicals that are used in lawns and farms. (3) Finally the lighted highways and security illumination that blazes all night around our homes and commercial buildings compromise the communication ability of adult fireflies.

FirefliesDrLallDr. Abner Lall (pictured right) is Professor Emeritus of Biology at Howard University (1988-2011) where his research over the last 30 years has been on the vision in fireflies. He began his investigation of vision and bioluminescence at Johns Hopkins University in the eighties (1979-88) as a research scientist. In his retirement, he is the visiting scholar at JHU, Department of Biophysics, Homewood Campus.



Summer’s in bloom!

Summer’s in bloom!

In addition to trees and pathways, trails and the mansion, there are many gardens at Cylburn with a variety of flowers of all kinds. In fact, Cylburn is classified as an arboretum, but is also one of Baltimore’s marquee public gardens. Summer is peak time for many of the beauties to be discovered on the grounds. Here are just a few you’ll find blooming now.

June Foxtail Lily 3

Eremurus sp. (Foxtail Lily)

This striking plant bears a tall stalk of yellow/orange-ish indeterminate flowers (“indeterminate” meaning that the flowers open from the base up, in contrast to “determinate” flowers which open from the top down).  This planting of Foxtail Lily bulbs attracts more “What IS that flower?” questions than most of the others.

Where: Across from the Mansion Circle, next to a weeping beech.

June Larkspur CloseupConsolida ajacis (Larkspur)

These bright blue and pink spikes are show-stoppers. Considered to be an annual alternative to delphinium, which struggles in this climate, the larkspur is an enthusiastic bloomer, and re-seeds itself every year. Larkspur is the “Flower of the Month” for July evoking feelings of joy, levity and love.

Where: Find them in the Mansion Circle and the Worthley Garden.

Asclepias tuberosa (Butterfly Weed)

This colorful native perennial is the sole host plant for Monarch butterflies, providing critical habitat for this endangered species.

Where: The orange variety can be found on the south edge of the Larrabee Garden and scattered other places. A less common yellow flowering cultivar ‘Mellow Yellow’ grows in the Mansion Circle.

June Butterfly Weed

June CactusOpuntia sp. (Cactus)

Bright yellow flowers prove that perennial cactus does grow and thrive in our non-desert climate! This one is surrounded by Sedum sexangulare (Stonecrop), a groundcover that can be found sprawling throughout many of Cylburn’s gardens.

Where: Find it in on the berm in the Worthley garden.

June Indian PinkSpigelia marilandica (Indian Pink)

This bright red and yellow native perennial grows in a large clump and is a favorite of hummingbirds. Although the genus name, Spigelia, honors Adrian van den Spiegel (1578-1625), a Flemish anatomist, the specific epithet, marilandica, means “of Maryland”.

Where: A large clump is found in front of the Vollmer Center, on the right as one faces the building. Also in the Larrabee Garden by the mansion.


June BetonyStachys densiflora ‘Hummelo’ (Betony)

This bright pink perennial has a long bloom season, from early June through July or even August. You can also find Stachys officinalis ‘Pink Cotton Candy’ by the Vollmer Center. Less well known that Stachys byzantina (Lamb’s Ears), these Stachys are well-behaved, dependable perennials with an orderly habit.

Where: In the Larrabee Garden by the mansion.

Whenever you visit Cylburn, keep an eye out for our What’s in Bloom posters. Thanks to our partners at Lifebridge Health for making these informative pieces possible for visitors. They’ll direct you with maps on where to find these flowers and others throughout the season. There are many gardens scattered throughout the grounds of Cylburn with more blossoms than can fit on one poster, so we hope you’ll explore! Find more info here. You may see our dedicated gardeners and volunteers out there planting, weeding or watering — They help to make all of this possible. We’re always looking for additional help so if you’re interested in joining our efforts you can find more information on how to volunteer here, or how to become a member here. Before you go, here are some more of this season’s blossoms!


Clockwise: Agastache rupestris (Threadleaf Giant Hyssop); Rudbeckia maxima (Great Coneflower); Rudbeckia (Black-eyed Susan); Hesperaloe parviflora (Red Yucca); Monarda ‘Jacob Cline’ (Bee Balm); Salvia ‘Purple rain’; Ratibida (Prairie Coneflower); Asiatic lily; Biker circling the Circle Garden; Hypericum calycinum (St. John’s Wort); and Mansion Garden.