mysterious large cocoon with a caterpillar inside.
April 5, 2010
I found him on the ground in my yard in Costa Rica. I brought it inside to hatch, but he just comes partially out to eat and poops round pellets out of the bottom, and spends most of his time inside. I have had him for about 5 days now. He has moved about to different locations, until i found a place he likes with leaves he likes to eat. He attached himself to a branch i provided with a small silk thread, and has remained there.
Is it normal for a caterpillar to continue to eat after spinning a cocoon, or is this his protective living space? Will it eventually pupate?
Costa Rica, Central America 3000 feet altitude.
We intended to post your photo two days ago, but we got distracted. The number of letters that are arriving each day has drastically risen since the first of April, and it is becoming impossible to even respond to a small fraction. Your submission is so unusual, and we are hoping one of our readers, perhaps Karl who just returned from Costa Rica, will be able to assist with this creature. Normally, we would think that a caterpillar of this kind would be a Bagworm, but we don’t believe that is the case here because Bagworms generally incorporate plant material in their bags.
Do you know the plant it is feeding upon?
I initially thought this might be a Sack-bearer Moth (Mimallonidae) but the caterpillar itself just doesn’t look right. I am therefore going back to the Psychidae (Bagworm Moths), some of which look very similar to the caterpillar in Jan’s first photo. I can’t be certain about a more specific identification but I think the genus may be Oiketicus, possibly O. kirbyi which is widespread throughout the tropical Americas and Caribbean. Assuming that it is O. kirbyi, the caterpillars do incorporate plant material into their bags as you indicated, but in this case the silk that binds the material together often envelopes the bag entirely. The result is a “lumpy” looking bag, much like the one in Jan’s photos. Females in the genus never leave their bags (except to die) and don’t develop wings, so Jan may be disappointed if she is expecting a winged moth to eventually emerge (unless it is a male). Oiketicus kirbyi has caused some problems in Costa Rica and other places as an agricultural pest. Regards.