Raising Monarchs

Monarch butterflies could still be observed making their way south last week, although we are now past the peak wave of these incredible migrants en route to their traditional overwintering grounds south of the border.

This epic journey, and the plight of this beautiful and easily recognized species, has received much attention in the media over the last two decades, and that attention has spurred many individuals, school groups and conservation organizations into action.

Among these actions are annual “watches” by citizen scientists to track monarch sightings, and creating habitat in the form of milkweeds for adult monarch to lay eggs on and for the hatched larvae (caterpillars) to feed on and develop. I was not aware that you could also purchase monarch eggs and larvae from captive-raised adults to raise at home or in school to enhance the local population.

The results of a recent study, titled “Contemporary loss of migration in monarch butterflies,” published this year in the Proceedings of the National Academy of Sciences, cast some doubts and notes of caution on the practice of raising monarchs in captivity for later release into the wild.

The scientists raised monarchs from eggs laid by wild-caught and commercially purchased butterflies. The larvae of each were kept outdoors in separate net-enclosed milkweed nurseries, where they went through their various instar stages and eventually morphed into chrysalises to begin their pupal stage. In late summer and autumn, the newly emerged adult butterflies were placed into a device that tracked the directions of their respective flights.

Progeny of the wild-caught monarchs oriented southward, as expected; those of the captive-bred butterflies showed no directional preference. Genetic testing of the latter group derived from a commercial source revealed that they were distinct from any wild monarch population.

The researchers pointed out that non-migratory monarch populations do exist, but this commercial source was determined to be descended from migratory stock. The study concluded that just a few generations spent in captivity had somehow altered their ability to migrate.

Since all the captive-bred butterflies came from one commercial source, it is not known how universal the loss of migratory instinct is among captive-bred stock.

Another portion of the study gathered monarch eggs from the wild and raised them in an incubator that simulated autumn conditions, a technique used by hobbyists dedicated to raising monarchs for release to join the late summer and fall southward migration. These also failed to fly south.

The study team writes: “We do not know what specifically about the indoor environment prevents the development of migration behavior … Our results provide a window into the complexity — and remarkable fragility — of migration.”