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Jennifer Krauel

Exploring aeroecology and life in the night sky

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  • About me
    • CV
    • Publications
    • Reflections
  • Aeroecology
  • Research
  • Blog
  • Media
  • Contact
  • Search
Photo: monarch butterflies gathered in a tree

Insect Migration

Insect migration is amazing

Photo: marmelade hoverfly
The marmalade hoverfly (Episyrphus balteatus) is an economically-important pollinating migrant. © Hans Hillewaert / , via Wikimedia Commons

Migration is fascinating, but few people realize that the vast majority of migratory animals are insects. Four to six billion dragonflies were seen migrating in Argentina. 100-200 million monarchs move across eastern North America. Contrast that with “only” 1.5 million wildebeest. Migration happens in all the major kinds of flying insects, especially grasshoppers, aphids and planthoppers, and butterflies and moths. Some make amazingly long voyages – scaled to body size, the longest are 25 times longer than that of large birds.

Insects migrate wherever temperatures are warm enough. Most of that migration is dependent on wind. Powerful fliers can move closer to the ground, but most fly hundreds of feet high where they can take advantage of very fast winds, and reach migration speeds similar to that of birds. But aside from the monarch, we actually know almost nothing about where these insects go, when and how they get there, or even why they do it.

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Insect migration is unexplored

Photo: fall army worm eating corn
Fall armyworm (Spodoptera frugiperda) is a serious pest on crops such as corn. Photo: Scott Stewart

Our lack of knowledge here should alarm you. Many migrants are serious agricultural pests responsible for considerable economic damage (although some are parasites of those pests). Some can spread disease to plants, people and livestock. On the other hand, many migrants, including hoverflies, are pollinators and we rely on their periodic arrival for our crops. Others represent seasonally important food sources for other animals, including bears and bats.

We have no idea of the true extent of negative or positive effects of migratory insects, and we’re barely starting to even ask the research questions that will reveal the answers. And because insect migration is based on weather, it is very likely to be disrupted in unpredictable ways by climate change. Insect numbers are already dropping worldwide and we don’t know why, and so we may lose these enormous migrations before we even understand them.

Insect migration is unique

Photo: monarch butterflies
Monarch butterflies (Danaus plexippus) in Texas in October

Besides the sheer volume, insect migration is also special because it differs fundamentally from familiar migrations, such as birds, in a fascinating way: each migration round-trip spans multiple generations. In monarch butterflies, for example, each annual 2,000+ mile journey involves 3-4 different generations, and no individual makes a repeat journey. This means they had to evolve innate ways of knowing when to leave, which way to travel, and when to stop. Reproduction is also tricky, and many species delay mating until after they arrive at a suitable place to lay eggs.

These aspects of insect migration mean that scientists studying them can’t rely on what they know about other kinds of migrants. It also means that insect migration is likely to have unique conservation requirements, since breeding habitats aren’t restricted to summer and wintering grounds. And for most of these insects, migration routes cross international borders, which further complicates conservation efforts. But without basic understanding of their migration biology it is very challenging to understand how best to protect them.

Origins of insect migration

Photo: silver y moth, by NobbiP
Silver Y moth (Autographa gamma), NobbiP [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.5-2.0-1.0], via Wikimedia Commons
Migration has evolved many times in insects, despite their ability to wait out bad conditions using diapause (a little like hibernation). You might ask why insects don’t use diapause instead of migrating, which is surely dangerous and expensive. We do have some insights on the answer to that question for one species, the Silver Y moth, which travels 375 miles between England and the Mediterranean basin in as little as 3 nights on high-altitude favorable winds.

Migration allows the Silvery Y moth to reproduce year-round, and simulations based on wind movements show that 80% of migrants would be able to find optimal habitat at their destination, a surprisingly high survival rate. Migrants have more offspring and higher population growth rates, and lower rates of parasites and disease. For the Silver Y moth, this meant the evolution of complex behavior: taking off to assess favorable winds hundreds of feet aloft and returning to the ground if the winds aren’t right, and adjusting headings to compensate for drift if the winds are slightly off. Only 4% of moths in the same family (Noctuidae) have evolved such long-distance movements, so most must rely on diapause to survive hard times, but the benefits for migration are clear in this case.

While most insect migrants are elusive, some are quite common. Here’s a great resource on common migratory butterflies and dragonflies in North America and how you can use your own garden to help them.


Questions? Comments? There’s more information in the blog entries below, but please feel free to start a conversation with me on Twitter: Tweet to @batgrrl

Photo: scientists carrying Helikite across a grassy field

What’s going on up there?

July 12, 2018

What’s going on up there?Read More

Screen shot: Free-tailed bats adjust foraging behavior in response to migratory moths

Bats adjust foraging behavior in response to migratory moths

May 1, 2018

Bats adjust foraging behavior in response to migratory mothsRead More

Screen shot of a radar showing echos of bats and insects

The Batscan!

April 12, 2018

The Batscan!Read More

Photo: Insect migration researchers answers questions after the symposium

Igniting the future of insect migration research

February 19, 2018

Igniting the future of insect migration researchRead More

Screen shot: Predator-prey interaction reveals local effects of high-altitude insect migration

Bats eat migratory moths! Lots of them!

February 11, 2018

Bats eat migratory moths! Lots of them!Read More

Screen shot: Weather-driven dynamics in a dual-migrant system: moths and bats

The answer is: cold fronts.

September 13, 2015

The answer is: cold fronts.Read More

Map of fronts, high and low pressure, and wind over the US

A river of life flowing overhead in the dark

October 6, 2013

A river of life flowing overhead in the darkRead More

Cloudlab images on Flickr

cloud lab photos on flickr

September 25, 2013

cloud lab photos on flickrRead More

Photo: BBC cloud lab airship on the ground in Florida

What if the BBC decided to do a show about your dissertation research?

September 22, 2013

What if the BBC decided to do a show about your dissertation research?Read More

Photo: Rustic arrow sign pointing up a hillside trail

Why Migration?

July 29, 2013

Why Migration?Read More

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Your AeroEcoTour Guide:

mmHi, I'm Dr. Jennifer Krauel. I’m an ecologist who's fascinated by animal migration, especially when it comes to bats and insects and at high altitudes. My research is driven by a deep desire to conserve and protect biodiversity. Read more »

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