Unknown critter on Marion blackberries

Asked October 9, 2015, 5:33 AM EDT

I have attached some photos of a critter that lived on my Marion blackberries earlier this year in Tokyo, Japan. It is some sort of a bagworm or such, since you can see that it has covered itself with various pieces of trash that it found useful. It now appears to be in pupa form hanging on the inside of a lid to a glass jar. It produces some silk to attach itself. It ate very sparingly over 2 months before pupating. Its dark-brown scat is unusually angular, rather than round.

Outside United States insect identification blackberries

4 Responses

I agree that the "critter" on your blackberries is most likely some kind of bagworm, which is actually a caterpillar in the moth family Psychodidae. Unfortunately, I am not familiar with any of the possible bagworm species found in Japan, nor could I find any information on the web or in my literature about Japanese bagworms, so I can't give you a more definitive identification. But the many species of bagworm caterpillars spin silken cases that they cover with bits and pieces of the plants that they feed on or other pieces of trash to help camouflage themselves. About all you ever see of the caterpillar is its head and first few legs that it uses to crawl around with, dragging the case behind it. When the caterpillar is grown, it forms its pupa inside the case, and eventually the new adult moth emerges. The frass pellets (scat) are typical for those expelled by caterpillars, the result of its passing through the hind gut of the caterpillar which has longitudinal ridges and channels that give the frass its particular shape. You actually will have a better chance of identifying this bagworm once the adult moth emerges. However, you may need to find a moth expert in Japan to be able to identify it.

Dr. Parsons:
Many thanks for your nice and informative reply. Indeed, I am hoping that "critter" will unfold his/her wings in Spring 2016.
BTW, I discovered critter purely by accident, with echoes of Fleming's stumbling upon penicillin: I had picked a clump of blue plastic ribbon trash off a Marion stalk and threw it in my office trash can, only to see it high on a nearby window the next day! Needless to say, I was dumbfounded. But I realized I had something of great value...or least great interest.
This is the first and only time I have seen this insect, at least in its camouflage suit.
I was also surprised that it ate so little, taking about 2 months to stop moving/eating and then pupating. I had thought that lepidoptera larvae were normally in a bit of a hurry to get to the next stage.
Could you enlighten in that regard, i.e., the lengthy process?

L. Stiver

I can't give you any specific information about the life cycle length of your specific critter since I don't know what species it is. But caterpillars in general may have many different kinds of life cycle attributes. The length of the different life stages, egg, caterpillar, pupa, and adult, may depend on many factors, which stage is the overwintering stage, what the caterpillars feed on, temperature, and how many generations a year that they have. Tropical species in warm climates often have many generations a year, so their life cycles are rather "speeded up", and the caterpillar stage may only be 1-2 months. Species that live in cooler climates may only have one generation a year, and the caterpillar stage may be extended and take several months to complete development. If the caterpillar stage is also the stage which overwinters, then it may extend 6-8 months or more. Food quality or abundance may also shorten or extend the life cycle. During warmer temperatures, caterpillars can be more active and feed more, which will help them develop faster. However colder temperatures will slow them down or even stop them from feeding altogether until it warms up again, which could prolong the development. So I don't really know which of these might apply to your specific critter. I suspect your "bagworm" would normally overwinter as a pupa inside its case. It probably only has one generation a year, so likely has a longer stage as a caterpillar than others. And because they are less mobile, and spend more time making and repairing their cases, they may not feed as often and that could prolong things too.

Thank you for again taking the time to compose a thoughtful response.
I should have noted that I was surprised by the long feeding period because Critter is pretty small, not at all like the larvae of big moths, which naturally spend several months eating.

Best regards.