The Winter Firefly

Hey, surprise! Some adult fireflies never.even.light.up 😳.

Yeah, I know it sounds weird. Yet based on shared ancestry (including their bioluminescent larvae), these so-called “dark” fireflies are authentic card-carrying members of the family Lampyridae. Common from coast to coast, each spring they quickly dominate the iNaturalist observations that show up in our Fireflies of the USA and Canada project.

Winter fireflies range 6-16 mm long

One of my personal favorite creatures happens to be the winter firefly, Ellychnia (ee-lick-ne-ah) corrusca, a species complex that’s widespread across eastern North America from Florida to Ontario. (In all, there are 12+ species in the genus Ellychnia, including several species found just on the west coast – reference below).

Easy to recognize, our eastern Ellychnia corrusca adults sport oval-shaped bodies, entirely dark wing covers (no pale margins), and a distinctive color pattern on their pronotum: a big central black spot is edged with red and enclosed within two pale parentheses.

Winter fireflies earn their common name from the fact that their adults can survive sub-freezing temperatures. Each fall in New England they gather on particular trees – they seem to frequent the same trees year after year – where they wedge themselves into grooves and hunker down to spend the winter. And they are decidedly hardy – in Massachusetts, Jen Rooney and I did a mark-recapture study and found 90% overwintering survival!

Last May this pair stayed together on my window screen for 17 hours.

In early spring, just when the maple trees begin flowering, winter fireflies start crawling up tree trunks. As temperatures rise, they begin flying through forested habitats in search of mates. Pairs mate in tail-to-tail position,  then the female flies off to lay her eggs. 

Like all fireflies, Ellychnia larvae are carnivorous. Rarely seen, they live and hunt within decaying wood. Hatching out in early summer, these larvae will spend the next 16 months eating and growing. Not until late summer of their second year will they transform into adults, which gather again on trees to overwinter.

 WIthout any lanterns, distinguishing between an Ellychnia female and a male requires a pretty close look at the underside of their abdomen. In females (below right), the last segment is triangular with small notch ; in males (below left), this segment is rounded and unnotched.

Personally, I don’t even care that they don’t light up – I love greeting these dark fireflies each spring! After a long winter, they bring a welcome promise of warm summer nights & lights ahead. So keep your eyes peeled and enjoy these unusual fireflies!

Further reading?

Jen Rooney & Sara Lewis, 2000. Notes on the life history and mating behavior of Ellychnia corrusca. Florida Entomologist 83: 324-334.

Kenneth Fender, 1970. Ellychnia of western North America. Northwest Science 31-43.