The fallen monarchs

Last winter, we found a monarch chrysalis that had fallen to the ground.  We brought it inside and several days later the story ended happily as the monarch successfully emerged and took flight.  This winter, falling was still a danger -- my mother found two chrysalises on the ground -- but there were also more serious threats lurking in the garden.

The remains of a caterpillar that had begun to form a chrysalis.

When I arrived in Florida and surveyed the garden, the only monarchs that I found were a caterpillar that had died while metamorphosing into a chrysalis (possibly due to disease or parasitism) and a chrysalis that did not look much healthier.

Something seems to have gone wrong for this monarch chrysalis.

The chrysalis was a dark brown color instead of bright green.  Although a healthy monarch chrysalis should turn dark shortly before the butterfly emerges (see here), something was wrong in this case -- the monarch's wing pattern was not visible.

A few days later, the chrysalis was still intact... but empty.

After a few days, the chrysalis was hollow with no obvious sign of what had happened to the butterfly that had been developing inside.  Meanwhile the chrysalises that my mother had rescued from the ground were also brown and hollow.  What had happened to all the monarchs? 

Pupae (left) from the flies that parasitized this monarch chrysalis (right).

Looking in the container below the rescued chrysalises, we found several pupae. These pupae belonged to flies -- flies that had parasitized the chrysalises and then emerged instead of the butterflies.  Unfortunately, since the container was not sealed, the adult flies had already escaped.