Imperial Caterpillar Ecdyses into Fourth Instar

Our oldest third instar Imperial caterpillar (Eacles imperialis) ecdysed into fourth instar.

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Yesterday, our oldest third instar Imperial caterpillar entered apolysis for fourth instar. Throughout most of the day today, it was still in apolysis with its head capsule quite loose. However, some time during the evening, it ecdysed into a black form fourth instar. We were assuming it would probably be a brown or green form, but it seems we were wrong since this individual is pitch black in color -- even darker than it was last instar which was already very dark. Its head capsule, body and horns are all completely black. Asides from color change, its white hairs are much longer and thicker, thus making them very easy to see, especially on the black body. Shape wise, there are some proportional differences. All horns/soli on the body have been reduced from last instar. The four large thoracic horns are now short and thick and are uniform in color from base to tip. The large middorsal horn which used to be the same six as the thoracic horns is now reduced into a tiny spike that is almost unnoticeable. All the remaining small scoli along the body are now almost completely gone and cannot be seen through the long white setae; they will likely disappear completely later in the instar as the body gets plumper and stretched. We were somewhat disappointed that this one became a black form since its not a very attractive color, though we will definitely see all the color forms after the others molt into fourth instar! This individual spent approximately 6 days in the third instar from 8/29-9/4 which is quite fast since  second instar lasted 6 days and 12 hours from 8/23-8/29 and first instar took 7 days from 8/26-8/23. There are currently 3 more third instars in apolysis which will probably ecdyse tomorrow or the day after.

Fourth Instar Imperial Moth (Eacles imperialis) Caterpillar Eating Pine (1)

​Fourth Instar Imperial Moth (Eacles imperialis) Caterpillar Eating Pine (2)*

*Shown in 8x speed

- Alan