What If Gone

Species → Monarch butterfly

Monarch butterfly

Danaus plexippus

western population: from ~10 million in the 1980s to 1,914…
Extinction risk Endangered
PollinatorMigrationInsectSingle host plant
Monarch butterfly (Danaus plexippus)
Photo: Derek Ramsey, Wikimedia Commons (GFDL 1.2)

What if it disappeared?

Impact Moderate
One reproductive cycle

Without milkweed in the right place, the monarch butterfly simply cannot reproduce — its caterpillar feeds only on plants of this genus, a strict dependency that makes the monarch population directly sensitive to the loss of this plant from a region. What the monarch's own disappearance would change for the ecosystem — pollination as an adult, the food chain of the few predators that tolerate it despite its toxicity — is, by contrast, far less documented.

Documented
Detail

Pleasants, J.M. et Oberhauser, K.S. (2013). Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. Insect Conservation and Diversity, 6(2), 135–144.

Milkweed is the only plant on which the female monarch lays her eggs and the only one the caterpillar feeds on. This strict dependency on a single host-plant family is what makes the monarch population directly sensitive to the loss of this plant from a region.

Over decades

The disappearance of milkweed from cultivated fields in the American Midwest, eliminated by the widespread use of herbicides on tolerant genetically modified crops, is statistically associated with the decline of the eastern monarch population.

Documented
Detail

Pleasants & Oberhauser (2013), op. cit.

By comparing the change in milkweed-covered area in Midwest corn and soybean fields to that of the monarch population overwintering in Mexico, the authors establish a strong statistical link between the loss of the agricultural host plant and the decline of the breeding population.

Documentation

Last verified: August 7, 2026