Newly emerged female.

 

Female underside.

 

Mates. (Darker colored male at left.)

 

July 2nd. Hatching day. About 3mm long.

 

 

 

July 4th. Early instar Promethea larvae are gregarious, feeding and resting side by side.

 

 

 

July 6th.

 

July 7th.

 

This group of caterpillars fed on a single leaf in parallel over several days, retreating up the leaf as they fed. Promethea larvae are always found feeding on the underside of leaves (even when in captivity, the undersides of the leaves sometimes face upward).

 

July 13th. Part of a shed skin can be seen at the bottom right. I'm not sure if these are 2nd or 3rd instar larvae. (Help?)

 

 

 

 

 

July 20th.

 

 

 

Molting has begun to the next instar. This larva has just shed its skin. The black color of the tubercles and some skin markings has not developed.

 

 

 

 

 

July 23rd. Here the yellow abdominal tubercles are starting to turn black.

 

This more mature larva has fully black tubercles.

 

The light skin color seems to be a coating of some sort; perhaps a waxy exudate? In any case, you can see areas where it has flaked off.

 

 

 

 

 

July 30th. Smaller larvae still look much like the photos taken on July 23rd. As the larvae grow, the black stripes diminish and disappear.

 

Then the yellow thoracic tubercles darken to orange...

 

...and then to a vibrant red. The spines on those tubercles are absorbed. This caterpillar is roughly 29mm long.

 

 

 

 

 

August 4th. The largest of the caterpillars is roughly 50mm long.

 

 

 

 

 

 

 

 

 

August 10th. The largest caterpillar (50mm+) spun a cocoon in the last two days. A cherry leaf forms a temporary shell for the silken cocoon inside. Over the winter, much of the leaf will dry and fall away, revealing the cocoon.

 

As the caterpillar begins spinning, step one is to attach the leaf petiole to the stem so that it will not fall off in the autumn.

 

The remaining caterpillars are in the 37 to 45mm range and growing fast. I expect they'll spin cocoons within the next week.