Cecropia Caterpillars Molt Into Fourth Instar

Our first three third instar Cecropia caterpillars (Hyalophora cecropia) have ecdysed into fourth instar.

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After nearly two days in apolysis, all three of our oldest third instar Cecropia caterpillars ecdysed into fourth instar this afternoon between 1:30-2:00 PM. The plum feeder was the first, followed by the apple eater shown in the three photos below, and finally another apple eater shown in the time lapse photos. One of the biggest differences between the fourth instars and third instars is that the rows of black spots between the tubercles is completely gone between the dorsal rows of tubercles, and nearly completely gone between the lateral rows of tubercles (in the first picture you can see tiny black speckles if you look closely enough). Another difference to note is that the body color is more bluish along the back and is even slightly translucent so that you can see the caterpillar's pulse (a greyish line going along the back as seen in the middle and right photos. Also, the five small lateral tubercles along the true legs and A1-2 are now clearly blue as seen in the left photo, not black. In addition, it appears that several tubercles may have gotten more black spikes at the tip (or maybe they were there last instar but too small and short to see), though it is hard to say for sure because they are so thin and often get broken when handling so the number of spikes on each tubercle may not be the true amount that it is supposed to have. Some obvious new black spikes can be seen on the red tubercles which now have seven spikes up from six, the blue thoracic tubercles which now have a sixth central spike in addition to the ring of five, and the large yellow middorsal tubercle on A8 which now has possibly eight or nine spikes up from six. The head capsule, tubercles, and legs are all huge now relative to the rest of the body but the proportions will even out as it grows bigger, since these three areas won't grow or will grow very little compared to the body.

Shortly after the individual in the first three photos molted, the third caterpillar in apolysis molted (you can see it starting in the background of the right-most picture). Since we already had the camera out, we took a ton (maybe a little excessive...) of time lapse photos of the caterpillar ecdysing shown below.

In addition to these three caterpillars molting, ten more have entered apolysis. Here are the numbers for today: L4: 3; L3+: 12; L3: 19; L2+: 0 ; dead: 2 (drowned)

Finally, for the record, today is the 21st day since the first caterpillars hatched, and marks the end of third instar for the oldest individual (the plum feeder), which lasted approximately 6 days and 17 hours from 6/20-6/27. Second instar lasted for roughly 6 days and 1-2 hours from 6/14-6/20, and first instar lasted for roughly seven days and 6 hours from 6/7-6/14.

-Alan