Bagworm Life Cycle: Unraveling the Mysteries of Nature’s Architects

Bagworms are fascinating creatures with a unique life cycle that impacts a variety of plants and trees.

From their intricate protective cases to their feeding habits, understanding the bagworm’s life cycle can help to better control infestations and protect vegetation in residential and commercial settings.

The bagworm’s journey begins early in June when they hatch from eggs that overwintered in the old bags attached to tree branches.

Bagworm Life Cycle
Bagworm

Upon hatching, these young caterpillars immediately start spinning their own bags, which they enlarge as they grow and feed on nearby plants.

Preferring to feed on conifers like arborvitae, cedar, juniper, and pine, bagworms can also attack deciduous trees such as sycamore, maple, locust, boxelder, and linden.

By recognizing and understanding the bagworm’s life cycle, we can better protect trees and shrubs from these voracious feeders and maintain the health and beauty of our landscapes.

Overview of Bagworm Life Cycle

Egg Stage

The life cycle of a bagworm begins with the egg stage. Female moths lay eggs inside their bag-shaped pupal case.

Each bag can contain about 300 to 1,000 eggs. These eggs usually overwinter and hatch in late spring or early summer.

Larval Stage

When the eggs hatch, bagworm larvae emerge and start feeding on nearby host plants. As they grow, these caterpillars create unique cone-shaped bags from silk and various debris, such as leaves and twigs.

The bag grows with the larva, reaching a size of 1/4 inch to over 2 inches depending on its stage of development. The larval stage lasts for a few months.

Bagworm

Pupal Stage

After they are fully grown, the bagworm larvae enter the pupal stage. At this point, the caterpillars attach their bags to the host plant and seal the opening.

During this stage, bagworms undergo metamorphosis and transform into adult moths. The pupal stage usually lasts 7 to 10 days.

Adult Stage

In the adult stage, male and female bagworms have distinct forms. Male moths are small, bee-like insects with clear wings, while female moths are wingless, legless, and remain inside their bag.

Mating occurs when the male moth finds a female by following the pheromones released by her. After mating, the female dies and her bag serves as an egg repository, continuing the cycle.

Bagworm Moth

Here is a comparison table of male and female adult bagworms:

CharacteristicMale BagwormFemale Bagworm
AppearanceBee-like with clear wingsWingless, legless
MobilityCan flyStays inside the bag
Role in reproductionMates with the femaleLays eggs inside the bag

Overall, the bagworm life cycle consists of four main stages: egg, larval, pupal, and adult stages.

From starting as an egg within the female’s bag, hatching into a caterpillar that feeds on host plants, pupating, and turning into either a male or female adult moth, this unique insect has a fascinating life cycle.

Biology and Behavior

Reproduction

Bagworms (Thyridopteryx ephemeraeformis) reproduce in late summer and early fall. The wingless females stay inside their bags, while the males transform into brown, fuzzy moths that can fly1.

Mating occurs when the male enters the female’s bag where she deposits her eggs2.

Feeding Habits

Bagworm caterpillars are most active from June to September, when they emerge and start to feed on both evergreen and deciduous trees.

For example, pine, juniper, and cedar are some of their favored evergreens, whereas deciduous trees such as maple, sycamore, and linden can also be targeted3.

Initially, these caterpillars can be found munching on leaves or needles4, but as they grow, they cause considerable damage to branches, leading to browning or foliage loss5.

Migration and Dispersal

Upon hatching, bagworm larvae disperse by crawling or getting carried away by the wind.

They construct a small bag, made from silk and plant materials, which they enlarge as they grow6.

As larvae move from one plant to another, they bring their bags along, infesting new areas.

Geographical Range

Bagworm moths are native to the eastern half of the United States2.

They can cause serious damage to a wide range of ornamental shrubs and trees in this region. Some commonly affected plants include:

  • Conifers (e.g., arborvitae, cedar, juniper, and pine)
  • Deciduous trees (e.g., sycamore, maple, locust, boxelder, and linden)

Their prevalence increases in urban settings and isolated trees, often escaping detection until significant plant damage has occurred3.

Conclusion

Bagworms are found in many regions of the world, where they feed on various plants. Their life cycle consists of four stages: egg, larva, pupa, and adult.

The eggs are laid inside the female bag and overwinter on the host plant. The larvae hatch in spring and start making their own bags as they feed.

The larvae pupate inside the bags in late summer or fall. The adult males emerge as winged moths and mate with the wingless females inside their bags. The females die after laying eggs and the cycle repeats.

Footnotes

  1. University of Nebraska-Lincoln  2
  2. Ohio State University  2
  3. University of Maryland Extension  2
  4. Purdue University 
  5. University of Delaware 
  6. Ohio State University 

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about bagworms. Scroll down to have a look at some of them.

Letter 1 – Bagworm and Giant Silk Moth Cocoon

Cocoons/Nests
Ok.  I’ve attached 3 photos below.  Thanks so much, Alanna

Hi Alanna,
There were no photos attached to this email.

On 3/6/09
Hi
I sent some photos late last month and wanted to check back with you
about the identification of them.  Our 7 year old girl thoroughly
enjoys all kinds of “BUGS” and can hardly wait for a response.
Thanks so much,
Alanna

Original Letter:  Feb 24, 2009, at 9:11 PM
cocoons/nests
I was wanting to know what we should expect
to emerge from these and how to possibly anticipate when (Can we
place these in a jar for observation until then?)?
Alanna
Metter, Ga

Bagworm
Bagworm

Hi Alana,
Sorry for the delay in getting to your response.  Additional delays resulted when you resent the request but we had no way of tracking your original letter with images.  Thanks for resending the images. 

You have provided an image of a Bagworm, a species of moth that lives its entire caterpillar life inside a bag consructed of silken thread and bits of plant material from the host plant.  Your other cocoon is some Giant Silk Moth. 

Both the Polyphemus Moth and Luna Moth wrap the cocoon in a leaf, and often the leaf falls to the ground, but occasionally the cocoon remains attached to the tree.  It appears as though the tree is a some sort of fruit tree.  Your third image which we are not posting, is of a Preying Mantis ootheca or egg case.

Polyphemus or Luna Cocoon???

Letter 2 – Bagworm Cocoon

Subject:  Pinecone-like Cocoon
Location:  Jacksonville, FL
August 27, 2015
Hi Bugman,
Today I found this
2 1/2″ long cocoon on a cedar tree.  It’s a brilliantly designed and constructed little pinecone-like structure. (It also reminds me of a log cabin.)
Would you please identify it for me?
Thank you,
L Welch

Bagworm Cocoon
Bagworm Cocoon

Dear L Welch,
This is the cocoon of a Bagworm, a species of moth in the family Psychidae.  A Bagworm Caterpillar constructs a shelter from silk and bits of the plants upon which it is feeding, enlarging the bag as the caterpillar grows. 

The caterpillar never leaves the bag, and eventually pupates inside the bag.  Your Bagworm is in the pupal stage, as it is no longer mobile.

Letter 3 – Bagworm Cocoon

Subject: Caterpillar?
Location: Clermont Florida
September 26, 2016 5:49 am
I found this on my window this morning when I opened the blinds. It was on the outside. I went out to look at it and it looks like it is making a cocoon? It looks like tree bark. The pictures were taken in Clermont Florida in September my me. I cannot find it anywhere on line.
Signature: Lynn Albanese

Bagworm Cocoon
Bagworm Cocoon

Dear Lynn,
This is a Bagworm Cocoon.  Bagworms are a family of moths, Psychidae, whose larvae construct “bags” out of plant material, generally the plants upon which they are feeding.  They carry around the bag for protection, and eventually pupate within the bag.  Your individual appears to have pupated.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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