Monarch butterflies on the Galápagos Islands!

In the life of any biologist, a trip the Galapagos Islands holds a special place. For me, I was gifted the opportunity to join a Cornell course focused on Evolutionary Biology by a colleague and friend. And as fate would have it, this trip in March of 2022 held several surprises, not the least of which was that my daughter Anna was able to join because of a last minute cancelation. What follows below is a photo-blog of our adventure, some of the great natural history, and an unexpected encounter with what was likely the most common insect on the islands, our very own Danaus plexippus. Although perhaps disappointing to some of you, I have purposefully not posted below images of the Magnificent Frigatebirds, several species of sharks, orcas, boobies, giant land tortoises, penguins, sea lions, marine iguanas, and other charismatic megafauna we saw.

Nearly 600 miles off the west coast of Ecuador, the Galapagos are a chain of volcanic islands that have been above water for a few million years
Arriving from Guayaquil
The red island, Rábida, known for it’s iron rich soils and sand. Appropriate for Cornell’s Big Red students
Likely Opuntia galapageia, an endemic prickly pear cactus, here growing in an arborescent form
Much to my surprise, monarch butterflies were one of the most common insect species I saw. Butterflies were abundant in the lowlands, but I didn’t see a single caterpillar
A milkweed vine, Funastrum angustissimum, another endemic to the Galapagos, but apparently not a host plant for the monarch caterpillar.  Although butterflies were super abundant in the lowlands where this plant was also common, caterpillars were not found here
Nonetheless, the ubiquitous Oleander Aphid (Aphis nerii, found on Apocynaceae on 6 continents) was reproducing on the Funastrum milkweed vine
The white-lined sphinx (moth), Hyles lineata. This species has a huge geographic range, all the way north to Canada and is known to have long-distance flights. It has a broad host range both as a caterpillar and adult
Also known as “puncture vine” because of its spikey seeds, Tribulus cistoides is an introduced plant that flourishes in the Galapagos
Seed predation by Darwin’s finches on Tribulus imposes natural selection on the seed spines (which reciprocally impose natural selection on the finches’ beak shape). An interesting research article on the topic is here
The Galapagos wild tomato, Solanum chessmanii, yet another endemic. This edible native has been used in breeding for insect resistance for the classic cultivated tomato we typically eat
Galapagos wild cotton, another endemic (Gossypium darwinii), a close relative of cultivated upland cotton. It’s in the hibiscus family (Malvaceae).
Euphorbia amplexicaulis, a Galapagos endemic in one of my favorite botanical families (the spurges)
Four or five senescent mats of that milkweed vine, Funastrum angustissimum, seen in the upper half of this volcanic hillside
An adult monarch Danaus plexippus seen in the highlands
The distribution of the “northern” monarch, Danaus plexippus, which is a distinct species from the Southern monarch, D. erippus. With nearly identical genomes, they were once thought to be the same species, although the publication below shows otherwise. Only the northern monarch has been found on the Galapagos to my knowledge


Danaus erippus, the southern monarch (photo from Wikipedia)
iNaturalist observations of the Southern Monarch (April 2022), note the largely non-overlapping distribution with D. plexippus
Much to still be discovered!
The tropical milkweed, Asclepias curassavica. Common in the higher elevations of the bigger islands, often associated with agriculture and grazing (because it is weedy and avoided by cows)
A late instar monarch, doing its thing — severing the midrib of tropical milkweed, with the distal portion of leaf hanging down, and the monarch going to town devouring the leaf
Monarch ggs
And a first instar caterpillar. After eating its chorion (the egg shell)


The tropical milkweed, Asclepias curassavica, in all its glory
What an adventure! In the background, Anna looks at flowing lava, orcas, or a hammerhead shark

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