When monarch butterflies wing their way south to central Mexico each fall, they use the sun to ensure that they stay on course. But how they head in the right direction on cloudy days has been a mystery—until now.
It turns out they use Earth’s magnetic field as a kind of backup navigational system.
It’s not unusual for animals engaged in long-distance migrations, including sea turtles and birds, to use an internal magnetic compass to get to where they’re going. But whether monarch butterflies have a similar ability had previously been unclear:
Some studies had found weak evidence for a magnetic compass, while others found none at all.
A paper published in the journal Nature Communications finally puts the issue to rest: The famous black-and-orange butterflies do, in fact, pack a magnetic compass.
Light-sensitive molecules called cryptochromes can detect small changes in Earth’s magnetic field, says study co-author Steven Reppert, a neurobiologist at the University of Massachusetts Medical School in Worcester.
And the cryptochromes in monarch butterflies need light on the UV-A side of the spectrum to operate.
Earth’s magnetic field lines radiate out from the South Pole, loop up around the Earth, and reenter the planet at the North Pole, Reppert says. That means there’s a gradient in the magnetic field from pole to equator.
When Reppert and colleagues put monarch butterflies in a flight simulator and manipulated the magnetic field and light levels, they found that the butterflies used changes in the magnetic field to orient themselves, rather than relying on the location of the North or South Pole.
“The dominant compass system [in monarch butterflies] is the sun compass,” says Reppert.
But their magnetic compass is a good backup system, since there are bound to be overcast skies on the way to their overwintering grounds.
Whether monarchs have a “magnetic map sense”—or the ability to know where they are in relation to their destination based on geomagnetic coordinates—remains to be seen.
“It’s a possibility which we’re about to explore,” Reppert says.
The viceroy butterfly appears similar in colour and pattern, but is markedly smaller and has an extra black stripe across the hind wing.
The eastern North American monarch population is notable for its annual southward late-summer/autumn migration from the United States and southern Canada to Mexico.
During the fall migration, it covers thousands of miles, with a corresponding multi-generational return North.
The western North American population of monarchs west of the Rocky Mountains most often migrate to sites in California but have been found in overwintering Mexico sites Monarchs were transported to the International Space Station and were bred there.
The Lord Howe Island phasmid (stick insect) is the world’s rarest insect and the entire population was limited to one bush on a remote sea stack.
Image Credit: Granitethighs/Wikimedia
by Becky Crew
FOR AN INSECT to be otherwise known as a ‘land lobster’, you know it’s got to be seriously big. The Lord Howe Island stick insect (Dryococelus australis) is a flightless, nocturnal insect that stretches up to 12cm long, and weighs 8-9g.
During the 19th century, this large insect prowled Lord Howe Island in such numbers that fishermen would use them as bait.
But then mice were introduced to the island, followed by black rats in 1918, and they made such a meal of these insect that by 1920 not a single one was recorded on the island.
By 1960 they were officially proclaimed extinct.
But in the late 1960s, sightings of stick insect remains were reported on Ball’s Pyramid – a volcanic remnant that sits 20km away.
Said to be the tallest volcanic stack in the world, Ball’s Pyramid is about 550m high, around 300m wide and 1 km long. It’s so narrow that there’s no way anyone can land a boat on it.
Instead, you have to anchor your boat in the ocean, launch yourself onto the vertical pyramid wall and climb your way up.
Many reckless explorers risked their lives to find a Lorde Howe Island stick insect here and bring the species back from the dead.
Piotr Naskrecki was taking a nighttime walk in a rainforest in Guyana, when he heard rustling as if something were creeping underfoot.
When he turned on his flashlight, he expected to see a small mammal, such as a possum or a rat.
“When I turned on the light, I couldn’t quite understand what I was seeing,” said Naskrecki, an entomologist and photographer at Harvard University’s Museum of Comparative Zoology.
A moment later, he realized he was looking not at a brown, furry mammal, but an enormous, puppy-size spider.
Known as the South American Goliath birdeater (Theraphosa blondi), the colossal arachnid is the world’s largest spider, according to Guinness World Records.
Its leg span can reach up to a foot (30 centimeters), or about the size of “a child’s forearm,” with a body the size of “a large fist,” Naskrecki told Live Science.
And the spider can weigh more than 6 oz. (170 grams) — about as much as a young puppy, the scientist wrote on his blog. [See Photos of the Goliath Birdeater Spider]
Some sources say the giant huntsman spider, which has a larger leg span, is bigger than the birdeater.
But the huntsman is much more delicate than the hefty birdeater — comparing the two would be “like comparing a giraffe to an elephant,” Naskrecki said.
The birdeater’s enormous size is evident from the sounds it makes. “Its feet have hardened tips and claws that produce a very distinct, clicking sound, not unlike that of a horse’s hooves hitting the ground,” he wrote, but “not as loud.”