THE HANDICAPPED MONARCH CATERPILLAR

Out of the 35 Monarch caterpillars I have raised so far, only one showed visible signs of abnormality. Yet it was still able to complete all its growth stages and successfully emerged as a female butterfly. However once released I had no way of knowing how it fared from then on.

That Monarch caterpillar had a problem with one of its prolegs and the area around it, and it became visible almost from the start. The abnormality also kept reappearing after each molt.

Even some of the droppings of that caterpillar were different, they had a different color than the usual dark green. In the last instar, the caterpillar also did not get as big and plump as the others I had raised, and its appetite was much lower.

Monarch caterpillar 1st instar on
July 25, doesn't look OK

Monarch caterpillar just molted on
July 28 with its handicap

Monarch caterpillar on July 30,
4th proleg area damaged

Close up of damaged proleg area,
July 30

Monarch caterpillar just molted again
July 30, old head still hanging

Monarch caterpillar with 4th proleg
turned backward, Aug. 1

Monarch caterpillar molted Aug. 4,
4th proleg area still defective

A few minutes after

Monarch caterpillar on Aug. 10,
proleg area does not look OK

Monarch caterpillar on Aug. 10,
one day before 'J' phase

Even the droppings of that Monarch
caterpillar looked different

Into 'J' phase with its handicap

The caterpillar was also slower than the others I have raised, and when the butterfly emerged as a female, it was weaker and could not use its lower pair of legs. Those were immobile and seemed 'paralyzed', to the point where it could not hold onto its empty chrysalis envelope and fell to the ground.

The abdominal tip of that female butterfly did not seem right either, although my photos and videos are not good enough to pinpoint exactly what was the issue.

The chrysalis color and shape were also different. It was more blueish than greenish like all the others, and it had some dark stains (grooves) in some areas. I wondered it those were a sign of a fungal infection. As for the shape, first it was smaller overall, and second the top part was narrower and more conical.

Then as it got darker and closer to emerging, another difference became apparent in that chrysalis - the surface was not smooth as the others I had raised. 

Chrysalis smaller, rough skin, dark
grooves, conical shape at top, Aug. 15

Compared with a normal chrysalis
in foreground, Aug. 20.

Different shape, smaller,
dark grooves, Aug. 20

Aug. 20 : handicapped Monarch
chrysalis will emerge soon

Aug. 21, shortly before emerging

Freshly emerged Monarch female,
can't use its 2nd pair of legs

Handicapped Monarch butterfly
only uses 1st pair of legs

Proboscis late to start unfurling

Abdominal tip does not
look normal

When released outside, that female Monarch butterfly also kept its upper wings on top of the hind wings when open, as we see for moths. I have yet to see such a posture in other Monarch butterflies.

Handicapped Monarch butterfly
holds its wings like a moth