Monarch Butterfly Populations Are Plummeting
Both Eastern and Western monarch butterflies are seeing their populations plummet precipitously, worrying scientists that the future of the species is in peril, according to multiple surveys of butterfly populations.
The New York Times recently reported on efforts to track the Western monarch butterfly, which spends its winter on California's central coast before heading off to breeding sites that covers a wide swathe from the state's central valley all the way to Idaho. However, recently it's been harder to find migrating butterflies.
"Something's going on in early spring," said Cheryl Schultz, a professor at Washington State University in Vancouver, to The New York Times. Researchers know that winter survival isn't the issue in the short-term, she said.
The researchers do not know if butterflies are not making it to breeding sites, unable to find mates, or starving along the way. What they do know is that the population of Western monarchs was in the millions in the 1980s, down to 200,000 three years ago, and then down to 30,000 in 2018, according to The New York Times.
Matt Forister, an insect ecologist at the University of Nevada, Reno, told the The New York Times that research identified various factors in butterfly loss, including development, climate change, farming practices and widespread pesticide use by farmers and on lawns.
On the other side of the country, expect to see far fewer Eastern monarch butterflies migrating over the summer. According to a new population survey, the Eastern monarch has passed the extinction threshold, according to a new population survey by the Center for Biological Diversity.
An annual count showed that the population in 2020 dropped 53 percent from its already low 2019 numbers. "Scientists were expecting the count to be down slightly, but this level of decrease is heartbreaking," said Tierra Curry, a senior scientist at the Center for Biological Diversity in a statement. "Monarchs unite us, and more protections are clearly needed for these migratory wonders and their habitat."
As Mongabay reported, the National Commission of Protected Natural Areas of Mexico teamed up with WWF-Mexico, local communities and other partners to carry out an annual survey of the forest habitat covered by monarch butterflies that migrate from the U.S. and Canada. The area of forest inhabited by monarchs in Mexican forests is then used to estimate the monarch butterfly population.
The amount of land they covered was about seven acres, down from 15 acres in 2019.
The Western monarch, which is slightly smaller and darker than the Eastern monarch, has a more constrained migratory pattern. While the Eastern monarch travels from Mexico all the way to New England and Canada, the Western monarch tends to stay around California, traveling as far north as British Columbia and east as far as the Rockies, according to The New York Times. However, in recent years, it has narrowed its path and does not make it as far as Washington.
Researchers and environmental advocates point out that stemming the climate crisis, reducing pesticide use and planting pollinator gardens could help the butterflies recover.
"Butterfly populations are bouncy," said Schultz to The New York Times. "While we think the situation right now is very concerning, we do think there's a lot of potential to turn it around."
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The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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