Within insects, pollinators often seem to get VIP treatment. Bees in particular get heralded for their role in helping plants set seed, produce fruit, and reproduce. While beetles aren’t usually the first group of insects to come to mind as pollinators, they actually have a long history in this role, with fossil records indicating that they were likely some of the first pollinators. Given that fireflies are beetles, you may be wondering whether fireflies act as plant pollinators.
Are you pollinating or just visiting?
Being an effective pollinator is not as simple as showing up at a flower. Pollination requires moving pollen from male parts of flowers (anthers and stamens) to female parts of flowers (pistils). In some cases, the pollen needs to be deposited on the female parts of a different flower or flowers of an entirely different plant of the same species. Insects that visit flowers range in their effectiveness as pollinators. Some bees, for example, exhibit “nectar robbing” behavior, bypassing the reproductive parts of flowers and instead chewing holes to access nectar. Other bees will collect pollen on their bodies and favor one species of flower, increasing chances that pollen will get where it needs to go for successful pollination. Yucca moths are extremely effective pollinators. The females moths collect pollen into tiny balls and deliberately presses these balls onto the pistil of a new flower.
Not all flower visitation results in pollination! The visiting animal might sip nectar without coming into contact with pollen or the flower pistil, simply use the flower as a place to perch or rest, or feed on petals or other flower parts.
A study of the pollination of an orchid species in China illustrates the important difference between visitation and pollination. Fireflies (Lampyridae) were some of the most frequent visitors to the cloud forest-dwelling orchid Holcoglossum rupestre , but in process they did not effectively remove the pollinium (pollen packets) from the flowers. A different species of beetle (a type of scarab), did effectively carry pollinia away, even though it made up a small percentage of total visits.
Winter fireflies and elf fireflies: floral visitors for all seasons
The humble, non-flashing winter firefly (Photinus corruscus) is one of the firefly species that is most frequently found on flowers, such as those of spicebush, asters, and goldenrod, and it may have a higher likelihood of being a pollinator compared to other fireflies. Because it is long-lived, it may have a greater need to feed, leading it to visit more flowers, both in the fall and the spring. Its forewings and head shield (known as a pronotum) also have subtle hairs that catch pollen grains, perhaps making them more effective transporters of pollen.
In the summer, when winter fireflies are absent, tiny diurnal fireflies in the genus Pyropyga can be found on flowers in gardens, fields and meadows. (Pyropyga have been affectionately nicknamed “elf” fireflies by firefly expert and field guide author Lynn Faust.)
Fireflies and milkweeds: toxic insect meets toxic plant
Fireflies of several types seem to have a unique association with milkweed (Asclepias) flowers. Adult fireflies can be found perched on milkweed flowers, sipping nectar but also touching various parts of the plant with their mouthparts. Milkweed pollen packets have also been found attached to fireflies, showing that these fireflies can effectively remove pollen from flowers.
Do fireflies benefit by visiting milkweed flowers?
Milkweed nectar is a sugar-rich food source, but it also is known to have toxins called cardenolides, which can actually harm the health of some pollinators (such as certain bumble bee species). Furthermore, milkweed flowers have slits that are meant to latch onto incoming pollen packets, but can also be death traps for unlucky insects.
Intriguingly, firefly larvae in the genus Photuris kept in captivity have been observed feeding on milkweed rhizomes (underground stems). It is possible that fireflies have evolved tolerance to milkweed toxins, and may even sequester these toxins in their bodies for their own protection, in a manner similar to monarch butterflies, milkweed bugs, and milkweed leaf beetles, though more research is needed to confirm this. We do know that fireflies also manufacture their own toxins, or acquire them by eating other fireflies (in the case of Photuris fireflies), so they do not rely on milkweed for this purpose.
Opportunities for community science and future research
There are several hundred observations on iNaturalist of fireflies visiting flowers, representing over a dozen species of firefly and many different types of plants. You can contribute to this data set by annotating iNaturalist observations of fireflies on flowers with the “Interaction->Visited flower of:” data field. These observations could inspire and provide a foundation for more formal scientific studies of flower visitation (and possible pollination) by fireflies. It will require carefully designed studies to clarify how much actual pollination (and of which plant species) fireflies are carrying out.
Lightning bugs as a back-up plan? The value of a diversified pollinator portfolio.
Fireflies likely play a relatively small role as pollinators in the ecosystem, but they do visit flowers and can occasionally be found with pollen on their bodies. In a rapidly changing and uncertain world, the flower visits made by fireflies may be source of resilience in cases where other pollinators are absent or scarce. Planting and maintaining a diverse mix of native flowering plants can be an important component of firefly habitat, and will support a suite of other animals (both visitors and pollinators) in addition to fireflies.
Further reading
Faust, L., & Faust, H. (2014). The Occurrence and Behaviors of North American Fireflies (Coleoptera: Lampyridae) on Milkweed, Asclepias syriaca L. The Coleopterists Bulletin, 68(2), 283. https://doi.org/10.1649/0010-065X-68.2.283
Jin, X., Chen, S., & Qin, H. (2005). Pollination system of Holcoglossum rupestre (Orchidaceae): A special and unstable system. Plant Systematics and Evolution, 254(1), 31–38. https://doi.org/10.1007/s00606-005-0310-z
Rooney, J. A., & Lewis, S. M. (2000). Notes on the Life History and Mating Behavior of Ellychnia corrusca (Coloeptera: Lampyridae). The Florida Entomologist, 83(3), 324–334. https://doi.org/10.2307/3496351
