Though it’s nearly mid October I saw monarch butterflies migrating through Pittsburgh on Thursday and Friday October 10 & 11. Their timing seems late, but they were given a boost by August-like weather early this month.

You can follow their progress across the U.S. on Journey North’s monarch butterfly blog where you’ll find:

• The long awaited peak migration has come.
• Monarchs streamed across Kansas and Oklahoma on 5 October, creating a butterfly front reported with video in the Washington Post.
• There was an amazing roost of 30,000 monarchs in Wiley, Colorado on 30 Sept.
• See the Fall 2019 monarch sightings map. Where are they now?

Today’s rain will put a damper on monarch migration in Pittsburgh but we can watch from afar as the butterflies make their way to Mexico.

(photo from Wikimedia Commons; click on the caption to see the original)

Now that the weather has changed unwelcome insects will invade our homes including Asian ladybeetles (Harmonia axyridis) that resemble native ladybugs but don’t act like them. Also called “harlequin ladybirds,” they overwinter indoors, make a stink, and bite when frightened.

A hundred years ago we thought this bug was a great idea and repeatedly introduced it to the U.S. to control aphids. The introduced ladybeetles never made it in the wild until a population was found thriving near New Orleans in 1988. After that they spread like wildfire across the eastern U.S. and into Canada.

Thirteen years later they became established in South America and Europe(*). By 2004 they were in southern Africa. They hadn’t been introduced. How did they get there?

A 2010 study of their genetic markers revealed that those three continents were invaded by the eastern North America population. In a move called the bridgehead effect, Asian ladybeetles in the U.S. used our continent as a jumping off point to colonize Europe, South America and Africa.

The bridgehead effect is now recognized as a method of worldwide pest invasion. The pest establishes a bridgehead — a strong position near a human transportation hub — then fans out from there. Ants, obscure mealybugs and brown marmorated stinkbugs have spread this way.

Who will be the next pest to establish a bridgehead? I hope it won’t be the spotted lanternfly.

Read more at: Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird.

(photo from Wikimedia Commons; map from PLOS One article posted at nih.gov. Click on the caption to see the original)

p.s. (*) The European population of H. axyridis is mixed. Some were directly introduced from their native range but were not considered pests until the North America cohort arrived.

In the American West there’s a 3-inch long katydid called a Mormon cricket (Anabrus simplex) that cannot fly but it sure can walk.

We hardly notice Mormon crickets until millions swarm and march across the landscape, advancing more than a mile a day like a Biblical plague of locusts. Naturally scientists wondered what makes them do it.

A 2006 study discovered that the swarms are driven by hunger and fear. The crickets are hungry for protein and salt so they start to migrate, but the bugs are cannibals and will eat each other if they can. Those at the back of the pack pursue the front line to catch and eat them. Fear forces the crickets to keep track of their neighbors and constantly on the move.

Despite the danger from behind, individuals sometimes double back into the crowd. If enough of them do it the whole swarm changes direction. How does this happen? What signals such a change?

In 2011, a study of locust swarming behavior at the Max Planck Institute worked on a computer model to predict the bugs’ behavior. Nothing adequately mirrored the swarms’ movements until researchers applied a social networking model that predicts the movement of human opinion on Facebook and Twitter. Somehow the locusts walking in one direction convince others to walk in the same direction. As researcher Gerd Zschaler remarked,

We concluded that the mechanism through which locusts agree on a direction to move together (sometimes with devastating consequences, such as locust plagues) is the same we sometimes use to decide where to live or where to go out: we let ourselves be convinced by those in our social network, often by those going in the opposite direction.

We don’t necessarily pay more attention to those doing the same as us, but many times [we pay more attention] to those doing something different.

— Swarms of locusts use social networking to communicate, Science Daily

Our crowd-based opinions move like swarms of locusts.

Swarms of locusts act like Facebook.

p.s. If you’ve never seen a swarm of Mormon crickets click here for a National Geographic video. Read more about locust swarming behavior in Science Daily.

(photos from Wikimedia Commons, click on the captions to see the originals)

In the past week I’ve noticed many monarch butterflies in flight and they’ve all been heading south.

When you see a monarch, pay attention to the direction it’s heading. Right now is the peak period for them to pass through Pittsburgh on their way to Mexico.

Monarch butterflies are on the move!

(photo from Wikimedia Commons; click on the caption to see the original)

In case you missed it, a monarch butterfly migration study published in the Proceedings of the National Academy of Sciences in June 2019 has troubling news for those who rear monarchs indoors.

Eastern monarch butterflies, famous for their autumn migration from North America to Mexico, have declined 80-90% in the last 20 years. To help the butterflies many people collect eggs and caterpillars in the wild and captive-raise them to increase their chances of survival. Unfortunately this well-meaning act can damage the insect’s ability to migrate.

Researcher Ayse Tenger-Trolander at Univ. of Chicago stumbled upon this when she purchased captive-bred butterflies for her monarch migration study. To measure their autumn migratory drive she placed them in a flight simulator and noted the dominant direction they wanted to fly. Wild migratory monarchs orient South. The captive-bred monarchs chose random directions, unlikely to migrate.

To further test the butterflies, Tenger-Trolander collected wild monarchs and raised a new generation indoors, mimicking outdoor autumn conditions. Here’s what she found.

Furthermore, rearing wild-caught monarchs in an indoor environment mimicking natural migration-inducing conditions failed to elicit southward flight orientation. In fact, merely eclosing(*) indoors after an otherwise complete lifecycle outdoors was enough to disrupt southern orientation.

Contemporary loss of migration in monarch butterflies, PNAS

Chip Taylor, Director of Monarch Watch, pointed out on NPR that some captive-bred monarchs do make it to Mexico, but added that “The real reason for raising monarch butterflies is for the enjoyment, the education. [T]he idea of individuals saving caterpillars as “monarch rescue” is misguided. “That’s simply not going to work as a way to boost the population,” says Taylor. “What we really need to do is to improve the habitat.”

We’re learning that monarch migration is complex and very fragile. It’s easy to break it in a single generation.

(photo by Kate St. John)

(*) “eclosing” means emerging from the chrysalis.