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Evergreen Bagworm Moth

Thyridopteryx ephemeraeformis


Bagworms are not really worms, but are caterpillars - they are the immature stage of a moth. They're called "bagworms" because they construct bags/cases that are covered with pieces of twigs and/or leaves. There are many of these bagworms on an arborvitae where I live. I never see the caterpillars during the day, so I decided to check at night, and actually found one peeking its head out! This is the case that it is living in. This case was 5 cm long


Spotted on an evergreen bush in a rural area.


In this species, the larvae emerge from the carcass of their mother in her pupal case. These newborn larva emerge from the bottom of the hanging case and drop down on a strand of silk. The wind will then blow them to a nearby plant where they can build their own cases made of silk, fecal material, and plant bits. Adult males transform into moths in about four weeks and immediately seek out females for mating. The females never leave the cocoon, but wait for a male to stick its abdomen through the opening at the end of her case so they can mate. Females do not have eyes, legs, wings, or antennae...and, they can't eat. After her death, her offspring hatch and then pass through her body and leave the case.

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Christine Y.
Christine Y. 5 years ago

Thanks Maria! They are really neat. I went back to check on them and found dozens on a couple bushes! Some had silk strands hanging out of them, which might be from the larvae leaving the cases. I’m going to keep checking and hope I can see a male at some point!

Maria dB
Maria dB 5 years ago

This is a very cool spotting, Christine. I wondered how the caterpillars looked that were inside these cocoons. And the information about their life cycle is very interesting! I'd never heard of a female moth that was always a caterpillar.

Christine Y.
Spotted by
Christine Y.

Connecticut, USA

Spotted on Aug 2, 2018
Submitted on Aug 9, 2018

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