After the structure is secured and the framework is completed, the larva then fills-in the gaps with a finer silk.
The outer-most layer is completed with very fine brown-colored silky substance which makes the outer shell non-transparent and fairly waterproof. This brown substance is initally wet, soft and pliable but dries to a stiff Tyvek-like quality in several hours. It's very fiberous
and tough, and will serve to protect the pupa inside from the elements for the entire winter. The entire outer layer building process takes about 2 - 3 days.
Even when the outermost layer is completed, the work continues inside. Paper-like scraping sounds can be heard as the larva builds a second capsule within the outer shell. A cut-away view shows how this inner capsule is
actually suspended within the outer shell by heavy silk. The gap between the inner and outer shells is a fairly consistent 1/8". At about 4 days from the start, the cocoon building process is complete.
Finally, the larva can rest before starting the pupation process. This second- layer cut-away view shows the larva inside. At this point, it has lost approximately half of its body mass from the cocoon making activity. Energy and physical material (silk) probably account for the bulk of the loss.
Note that the larva barely fits inside the inner shell. Even so, it is extremely flexible, such that it can still get its mouthparts (where the silk-spinning gland is located) to any part of the shell.
This larva attempted to repair the cut-away part of the shell shortly after the pictures were taken, so the cut-away part was replaced and held in place with tape so that the larva would not have to expend any further effort in repairing the damage.
After 11 days, the "pre-pupae" shows signs of molting, with loose and transparent skin. The hi-re image on the right was taken 6-14-2005.
On the 12th day, the final skin is molted, and the pupae begin hardening and compressing into their final shape. Note the green color. The wing, antennaecase, and abdominal segemnts are actually transparent, revealing the green "body" inside.
By the 13th day, there is only a little green color left, and the pupae looks more like one would expect - very dark brown and the classic shape. The large feathery antennae are a clear indication that this is a male.
In the wild, cocoons are very scarce but can be spotted under the right conditions. Here, a number of them can be seen in the nearly naked branches of these Cercocarpus (Mountain Mahogany) trees. Cercocarpus generally doesn't lose all of its foliage in winter, but in this case, most of it was gone, making the cocoons much easier to see.
Unfortunately, the pupae in all 5 of the cocoons found in this one spot were dead. The cause is unknown but after examining the pupae inside it appeared that they were moldy and dried-out. There were no signs of parasites in any of them. The second row shows contents of each cocoon on 6-18-2005.
These freshly spun cocoons were raised outdoors on Cercocarpus in 2005. They have a green tint to them as opposed to the tan-brown color of the ones raised indoors on Ceanothus. After a few days, the green faded somewhat, to more closely resemble the tan-brown coloration of the cocoons raised in 2004.
One of the cocoons was cut open to check the status of the pre-pupae inside. Note the inner and outer shells. 6-6-2005