Fireflies
threatened by habitat loss, pesticides, artificial light
Since their evolutionary
origin some 297 million years ago, beetles have been highly successful; they
represent 38% of known insect species. Fireflies rank among the most charismatic beetles, with distinctive bioluminescent courtship displays that make them a potential flagship group for insect conservation.
With more than 2,000
species worldwide, fireflies exhibit surprisingly diverse life history traits,
including nonluminous adults with daytime activity periods, glowworm fireflies
with flightless females, and lightning bugs that exchange species-specific
flash signals.
Fireflies also inhabit
ecologically diverse habitats, including wetlands, grasslands, forests,
agricultural fields, and urban parks.
Their predaceous larvae,
which can be aquatic, semiaquatic, or terrestrial, spend months to years
feeding on snails, earthworms, and other soft-bodied prey. In contrast, firefly
adults are typically short lived and do not feed.
Fireflies are
economically important in many countries, because they represent a growing
ecotourist attraction. However, as is true for many invertebrates, fireflies
have been largely neglected in global conservation efforts.
To better understand
what threats are faced by fireflies, Tufts University’s Professor Sara Lewis
and colleagues surveyed firefly experts around the world to size up the most
prominent threats to survival for their local species.
“Lots of wildlife species are declining because their habitat is shrinking, so it wasn’t a huge surprise that habitat loss was considered the biggest threat,” Professor Lewis said.
“Some fireflies get hit
especially hard when their habitat disappears because they need special
conditions to complete their life cycle.”
“For instance, one
Malaysian firefly (Pteroptyx tener), famous for its
synchronized flash displays, is a mangrove specialist.”
One surprising result
that emerged from the survey was that, globally, light pollution was regarded
as the second most serious threat to fireflies.
“In addition to
disrupting natural biorhythms — including our own — light pollution really
messes up firefly mating rituals,” said Avalon Owens, a Ph.D. candidate at
Tufts University.
Many fireflies rely on
bioluminescence to find and attract their mates, and previous work has shown that
too much artificial light can interfere with these courtship exchanges.
Switching to energy efficient, overly bright LEDs is not helping.
Firefly experts viewed
the widespread agricultural use of pesticides as another key threat to firefly
survival.
Most insecticide
exposure occurs during larval stages, because juvenile fireflies spend up to
two years living below ground or under water. Insecticides such as
organophosphates and neonicotinoids are designed to kill pests, yet they also
have off-target effects on beneficial insects.
While more research is
needed, the evidence shows that many commonly used insecticides are harmful to
fireflies.
A few studies have
quantified firefly population declines, such as those seen in the
tourist-attracting synchronous fireflies of Malaysia, and the glowworm Lampyris noctiluca in England. And numerous
anecdotal reports suggest that many other firefly species across a wide range
of habitats have also suffered recent declines.
The researchers also
highlight risk factors that allow them to predict which species will be most
vulnerable when faced with threats like habitat loss or light pollution.
For instance, females of
the Appalachian blue ghost firefly (Phausis reticulata)
are flightless.
“So when their habitat
disappears, they can’t just pick up and move somewhere else,” said Tufts
University’s Professor J. Michael Reed.
“Here in the U.S., we’re
fortunate to have some robust species like the Big Dipper fireflies (Photinus pyralis),” Professor Lewis said.
“Those guys can survive
pretty much anywhere- and they’re beautiful, too.”
By illuminating these
threats and evaluating the conservation status of firefly species around the
world, scientists aim to preserve the magical lights of fireflies for future
generations to enjoy.
“Our goal is to make
this knowledge available for land managers, policy makers, and firefly fans
everywhere,” said Dr. Sonny Wong, of the Malaysian Nature Society.
“We want to keep
fireflies lighting up our nights for a long, long time.”
The report was published in the journal BioScience.
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Sara M. Lewis et al.
A Global Perspective on Firefly Extinction Threats. BioScience,
published online February 3, 2020; doi: 10.1093/biosci/biz157