Weather anomalies are keeping insects active longer

As Earth's climate continues to warm due to the emission of greenhouse gasses, extreme and anomalous weather events are becoming more common. But predicting and analyzing the effects of what is, by definition, an anomaly can be tricky.

Scientists say museum specimens can help. In the first study of its kind, researchers at the University of Florida used natural history specimens to show that unseasonably warm and cold days can prolong the active period of moths and butterflies by nearly a month.

"The results are not at all what we expected," said lead author Robert Guralnick, curator of biodiversity informatics at the Florida Museum of Natural History.

Most studies view climate change and its consequences through a periscope of average temperature increases. As temperature goes up over time, the plants and animals in a particular region become active earlier in the spring, delay dormancy until later in the fall and slowly shift their ranges to align with the climate in which they're best suited to survive.

Erratic weather adds a layer of complexity to these patterns, with unknown consequences that erect an opaque screen ahead of scientists attempting to predict the future of global ecosystems.

"There had been hints in the scientific literature that weather anomalies can have cumulative effects on ecosystems, but there wasn't anything that directly addressed this question at a broad scale," Guralnick said.

This omission, he explained, was due primarily to a lack of sufficient data. While climate data has been reliably collected in many areas of the world for more than a century, records documenting the location and activity of organisms are harder to come by.

Natural history museums have been increasingly regarded as a potential solution. The oldest museums have accumulated specimens for hundreds of years, and recent efforts to digitize collections have made their contents widely available. But digital museum records come with their own unique pitfalls and drawbacks.

In 2022, study co-author Michael Belitz constructed a dataset of moths and butterflies from museum collections to chart a course for other researchers hoping to use similar data. The result was a comprehensive instruction manual for how to gather, organize and analyze information from natural history specimens.

With this robust resource at their disposal, Belitz and his colleagues wanted to see if they could detect a signal from aberrant weather patterns. Restricting their analyses to the eastern United States, the authors used records for 139 moth and butterfly species collected from the 1940s through the 2010s.

Their results were unequivocal: Unusually warm and cold weather has significantly altered insect activity to a greater extent than the average increase in global temperature for the last several decades.

The location and timing of extreme weather events influenced how insects responded. In higher latitudes, warm days in winter meant moths and butterflies became active earlier in the spring. Unusually cold days kept insects at all latitudes active longer, and the combination of exceptionally high and low temperatures had the strongest effect.

"If you have a succession of abnormally cold and warm days, it limits the ability of insects to function at peak performance," Guralnick said. "If cold doesn't kill you, it slows you down, and it might force insects into a torpor. Insects can recover from the cold snaps pretty quickly and go on to have longer lifespans as a direct result of sudden temperature declines."

Insects being active for longer periods of time might initially seem like a good thing. But rather than a counterweight to the negative repercussions of climate change, co-author Lindsay Campbell -- who studies mosquitos -- points out that longer or altered insect lifespans may also mean more opportunities for pathogen transmission.

"There's a correlation between El Niño and rift valley fever outbreaks in East Africa, and there are anecdotal observations that show unusually warm or hot and dry springs, followed by a heavy precipitation event, are also linked with increased outbreaks," said Campbell, an assistant professor at the University of Florida.

Long-term ecosystem stability is also entirely dependent on the synchronized activity of its constituent parts, and plants may not respond to extreme weather in the same way as insects. If moths and butterflies take flight too early, they risk encountering plants that haven't yet produced leaves or flowers, expending their energy in a vain search for food.

And with a constantly shifting baseline for what constitutes 'extreme,' it's unclear if insects will be able to keep pace with the changes.

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What is it good for? Absolutely one thing: Luna moths use their tails solely for bat evasion

In a pair of complementary studies, researchers took a close look at Luna moth (Actias luna) tails through the eyes of birds and female moths to test the tails' role in predation and sexual selection. Scientists have known for about a decade that Luna moths -- and other related silkmoths -- use their long, trailing tails to misdirect bat attacks.

"They have projections off the back of the hindwing that end in twisted, cupped paddles," said Juliette Rubin, a doctoral student at the Florida Museum of Natural History and lead author of both studies. "From experimental work with bats and moths in a flight room, we've found that these structures seem to reflect bat sonar in such a way that bats often aim their attacks at the tails instead of the main body."

Traits that evolve for one specific function can often be co-opted by natural selection for another, and Rubin wondered whether the twisted tails of Luna moths might come with any additional benefits or hidden costs.

Male Luna moths doff their tails, retain their charm

Silkmoths have independently evolved tails on multiple occasions across three continents, and the appendages can vary significantly in length. Hind wings in some species can extend to more than twice the size of the moth's wingspan, and the longer the tail, the more likely a moth will successfully thwart a prowling bat.

But far from being drab, utilitarian decoys meant only for sonar-sensing bats, silkmoth tails are often visually stunning, like decorative streamers trailing behind a kite. Across the animal and plant kingdoms, many of the most colorful and alluring structures are used to attract mates or pollinators, and scientists suspected the same might be true of silkmoth tails.

This type of dual function for a single trait isn't without precedent. The vivid colors of strawberry poison dart frogs (Oophaga pumilio) both deter predators and help males attract mates; male deer and other ungulates use their antlers to fight off rivals and signal their vigor to females; and moths that use clicks or chirruping sounds to disrupt bat echolocation can compose duets using the same sounds during courtship.

Luna moths have neither mouths to produce sound nor ears to hear it, but they do have sensitive eyes and powerful scent-detecting antennae. When female Luna moths are ready to mate, they perch in one place and emit a pheromone, a single molecule of which is enough to trigger a male antenna. The males of closely related Indian moon moths (Actias selene) can find females from more than six miles away by following the pheromone plume to its source.

"We don't know how many males are traveling to a female each night," Rubin said. "It's entirely possible she's able to call in multiple suitors and potentially have her pick."

Rubin put this idea to the test, setting up mating experiments in which a female Luna moth was enclosed in a flight box with two males: one with normal hind wings, and one with its tails removed.

Initially, the data seemed to suggest that females preferred males whose wings remained intact, but additional controlled experiments demonstrated that this was more likely an incidental effect of the tail removal. During trials in which both males had their wings clipped, and one had the tails glued back on, there was no difference in their mating success.

Do tails make Luna moths invisible to bats but conspicuous to birds?

Having demonstrated tail wings likely weren't conferring any additional benefits beyond survival, Rubin wanted to see whether they had any obvious drawbacks. Their long tails effectively throw off pursuing bats by creating a decoy target, but bats aren't the only adversaries Luna moths have to avoid. Their electric green tails with bright, pink parfait borders might make Luna moths noticeable to birds and other visually oriented predators that hunt during the day.

Other organisms contend with similar tradeoffs. The bioluminescent displays of fireflies make it easier for males to locate potential mates, but it also makes them stand out to nocturnal frogs and geckoes.

Luna moths live incredibly short lives, during which they can afford to lose a tail or two. Once they emerge from their cocoons, the moths have about a week to find a mate and reproduce before dying. "This creates a very intense period of adulthood, where surviving the night is of the utmost importance," Rubin said.

Luna moths are mostly inactive during the day, reducing their chances of being nabbed midair. If they don't do a good enough job concealing themselves, however, they run the risk of not surviving to nightfall.

Rubin wanted to know if their visually elaborate tails put Luna moths at a disadvantage in this high-stakes game of hide-and-seek. To find out, she and her colleagues wrapped mealworms in pastry dough in the shape and size of Luna moth bodies, to which they attached real wings, half of which had tails. They partially hid these moth replicas among branches and leaves in an aviary, then introduced a succession of Carolina wrens (Thryothorus ludovicianus), recording how many of the snacks the birds located and ate.

The results conclusively indicate that the tails had no effect on the birds' ability to locate the fake moths. This might seem odd to us, Rubin said, because we're such visually oriented animals. But there's evidence that suggests birds might rely on search images when trying to distinguish food items from patterns in the background.

Humans do this too. When trying to complete a Where's Waldo puzzle, people often look for the characteristic red, horizontal lines of Waldo's shirt while scanning across the page. It's possible that Luna moth tails don't match the typical moth and butterfly mold that birds expect to see while foraging, the equivalent of Waldo wearing a solid red shirt rather than his signature stripes.

While not indicative of all silkmoths, the studies suggest that these stunning and complex structures evolved for a single function in Luna moths.

"When we see these really obvious physical features in animals, we're often drawn into stories we've heard about them," Rubin said. "One is that conspicuous traits are for attracting mates or competing with rivals, and another is that these very showy traits must come with a cost. Both of these studies show it's really important to test those assumptions. A trait that's obvious to us, as visual creatures, might not stand out to the predators that hunt them, and the traits that we think are dynamic and alluring might not seem that way to a potential mate."

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New alpine moth solves 180-year-old mystery

Butterflies and moths (order Lepidoptera) are one of the most diverse animal groups. To date, scientists have found as many as 5,000 species from the Alps alone. Having been a place of intensive research interest for 250 years, it is considered quite a sensation if a previously unknown species is discovered from the mountain range these days. This was the case when a Swiss-Austrian team of researchers described a new species of alpine moth in the open-access, peer-reviewed journal Alpine Entomology, solving a 180-year-old mystery.

Decades of research work

Initially, the team -- Jürg Schmid, a full-time dentist, author and passionate butterfly and moth researcher from Switzerland, and Peter Huemer, head of the natural science collections of the Tyrolean State Museums in Innsbruck and author of more than 400 publications, needed a lot of patience.

Almost thirty years ago, in the 1990s, the two researchers independently discovered the same moth species. While they found it was similar to a moth of the leaf-roller family Tortricidae and commonly named as Dichrorampha montanana which had been known to science since 1843, it was also clearly different. Wing pattern and internal morphology of genitalia structures supported a two-species hypothesis. Moreover, the two were found at the same time in the same places -- a further indication that they belong to separate species. Extensive genetic investigations later confirmed this hypothesis, but the journey of presenting a new species to science was far from over.

The Hidden Alpine Moth

To "baptise" a new species and give it its own name, scientists first have to check that it hasn't already been named. This prevents the same species from having two different names, and essentially means looking at descriptions of similar species and comparing the new one against them to prove it is indeed unknown to science. In the case of this new moth, there were six potentially applicable older names that had to be ruled out before it could be named as new.

Intensive and time-consuming research of original specimens in the nature museums of Paris, Berlin, Frankfurt and London eventually led to the finding that all six ancient names actually referred to one and the same species -- Dichrorampha alpestrana, which has been known since 1843 and had to be adopted as the valid older name for Dichrorampha montanana as having been described a couple of months earlier. Similarly, all other available names proved to belong to Dichrorampha alpestrana. The species discovered by Schmid and Huemer, however, was different, not yet named, and could finally be described as new to science. The authors chose to name it Dichrorampha velata -- the Latin species name means "veiled" or "hidden," pointing to the complicated story behind its discovery.

Lots of unanswered questions

The Hidden Alpine Moth is a striking species with a wingspan of up to 16 mm and a characteristic olive-brown color of the forewings with silvery lines. It belongs to a group of mainly diurnal moths and is particularly common locally in colorful mountain flower meadows. For now, we know that its distribution extends at least from Salzburg and Tyrol through southern Switzerland and the Jura to the French and Italian Alps, with isolated finds known from the Black Forest in Germany, but the researchers believe it might have a wider range in Central Europe.

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