Monarch Butterfly Migration News

Monarch Butterflies

Finding Milkweed
May 4, 2017 by Elizabeth Howard

Monarchs travel hundreds of miles across the landscape in search of the milkweed they need for egg-laying. How do they find it?

"A faded female laying eggs on newly emerged milkweed - A. syriaca and A. incarnata."
Sighted April 27, 2017 in Lititz, PA by Kim Frey.

Waiting for the Surge
The lull between generations continues. The first half of May is always the slowest time of year, and this year is no exception.

Observers are seeing the last of the monarchs from Mexico and their physical descriptions are increasingly dire. These "torn, tattered, dull, faded, pale" butterflies may be 9 months old!

Hot and Cold
Monarchs reponded to this week's temperature extremes:

First sightings were reported as far north as New York City during a heat wave in the eastern U.S., where northern regions were as warm as Texas.
The migration's northward advance came to a halt in the Midwest where freezing temperatures and snow exposed monarchs to the risks of frost.

Finding Milkweed
Monarchs have an uncanny ability to find milkweed. This week they found some under a deck, beside a pool, in potted plants, wildlife parks, backyards and schoolyards, on milkweed that was just emerging and on plants in full bloom.

Milkweed isn't easy for us to find, so how do monarchs do it?

First for New York
Mary Pfeifer

Hot and Cold
Unisys

Risk of Frost
Elizabeth Howard

How Do Monarchs Find Milkweed?
More Slideshows

Monarchs find milkweed in places and ways that astonish observers. Kathryn Cole could not believe her eyes. "Milkweed just broke the ground yesterday and grew 3 inches in one day. We began checking for eggs and, sure enough, a monarch had already deposited her eggs on the newly emerging plants."

An Everyday Miracle Monarchs find milkweed in places and ways that astonish observers. Kathryn Cole could not believe her eyes. "Milkweed just broke the ground yesterday and grew 3 inches in one day. We began checking for eggs and, sure enough, a monarch had already deposited her eggs on the newly emerging plants."

Dr. Bill Calvert describes what he observes in the field:"The female flits over the field and, when she stops on a plant, she drums the surface with her forelegs." The forelegs are tiny, close to the head, and difficult to see. How do the forelegs help the female find milkweed?

A Touch of Milkweed Dr. Bill Calvert describes what he observes in the field:"The female flits over the field and, when she stops on a plant, she drums the surface with her forelegs." The forelegs are tiny, close to the head, and difficult to see. How do the forelegs help the female find milkweed?

"Monarchs use a combination of visual and chemical cues to find milkweed," says monarch scientist Dr. Karen Oberhauser. "Once they land on a plant, they use sensory organs on their feet and heads to tell them if it is a milkweed, and probably the quality of the milkweed."

A Combination of Senses "Monarchs use a combination of visual and chemical cues to find milkweed," says monarch scientist Dr. Karen Oberhauser. "Once they land on a plant, they use sensory organs on their feet and heads to tell them if it is a milkweed, and probably the quality of the milkweed."

It's difficult for scientists to study monarch's senses because an insect's senses are so different from ours. Yet even our own senses are mysterious. When we smell and taste we are actually sensing chemicals in our environment. People and monarchs do this in a similar way.

A Look at Senses It's difficult for scientists to study monarch's senses because an insect's senses are so different from ours. Yet even our own senses are mysterious. When we smell and taste we are actually sensing chemicals in our environment. People and monarchs do this in a similar way.

People and monarchs sense chemicals in the environment with special structures called chemoreceptors. They come in different shapes and sizes, but they work in the same way. When a chemical fits a receptor, the way a key fits a lock, the brain identifies the chemical.

Chemoreceptors ("KEE mo ree CEP terz") People and monarchs sense chemicals in the environment with special structures called chemoreceptors. They come in different shapes and sizes, but they work in the same way. When a chemical fits a receptor, the way a key fits a lock, the brain identifies the chemical.

Monarchs use their antennae to detect plant chemicals. The antennae are covered with chemoreceptors, especially at the tips.

Antennae Have Chemoreceptors Monarchs use their antennae to detect plant chemicals. The antennae are covered with chemoreceptors, especially at the tips.

All six of the female monarch's legs have chemoreceptors. Here you can see the midlegs. Look closely and you'll see the sharp spines monarchs can use to cut the plant and release the chemicals that tell the monarchs it's milkweed.

Legs Have Chemoreceptors All six of the female monarch's legs have chemoreceptors. Here you can see the midlegs. Look closely and you'll see the sharp spines monarchs can use to cut the plant and release the chemicals that tell the monarchs it's milkweed.

Eyes sense light, not chemicals. Monarchs have compound eyes with thousands of lenses, and see thousands of single images at the same time. Monarchs can see in all directions at the same time, too. They don't see the world in a single image the way we do. Their vision is specialized for seeing colors, direction and movement.

Eyes Eyes sense light, not chemicals. Monarchs have compound eyes with thousands of lenses, and see thousands of single images at the same time. Monarchs can see in all directions at the same time, too. They don't see the world in a single image the way we do. Their vision is specialized for seeing colors, direction and movement.

Some plant species grow together in groups called 'guilds.' Together, the plants defend themselves by producing a mixture of plant odors. Herbivores, like monarchs, can't find the correct host because there are too many confusing odors. This would explain why monarchs need to use a combination of senses to find milkweed.

Confusing the Senses Some plant species grow together in groups called 'guilds.' Together, the plants defend themselves by producing a mixture of plant odors. Herbivores, like monarchs, can't find the correct host because there are too many confusing odors. This would explain why monarchs need to use a combination of senses to find milkweed.

Picture a monarch floating through the air, following invisible scents to find the milkweed it urgently needs. Watch how a butterfly can locate milkweed that's hidden in a sea of green plants.

Field of Green Picture a monarch floating through the air, following invisible scents to find the milkweed it urgently needs. Watch how a butterfly can locate milkweed that's hidden in a sea of green plants.

Companion Resources

Driving Question

How do monarchs sense the world and which senses lead them to milkweed?

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Spring Migration 2017


Report all monarchs you see — adults, eggs, larvae.

What to Report	Adults report \| map \| list	Eggs report \| map \| list

Larvae report \| map \| list	Milkweed report \| map \| list	Other Observations report \| map \| list

Next May 11, 2017