Bagworm (Thyridopteryx ephemeraeformis, family Psychidae) caterpillars have “tied off” and are pupating in southwest and northeast Ohio. This marks a significant transition period in management options.

On the upside, pupation means the caterpillars have stopped feeding, so there will be no more bagworm damage this season. On the downside, insecticide applications will no longer work even though the bags remain evident. Don’t be fooled! Management now centers on a more hands-on approach.

Life in a Backpack

Both male and female bagworm caterpillars spend their entire larval development inside their silk bags. The bags have two openings at opposite ends. The caterpillars use the large upper opening to poke their heads out to feed and enlarge their bag abodes. They avoid plummeting from their plant hosts by anchoring their bags with a small bit of silk to their plant hosts.

Bagworm Feeding Behavior

Bagworm Caterpillar Extended

The lower opening serves as a toilet, which allows the caterpillars to shove out fecal pellets (frass). Otherwise, their bags would gradually become a heavy bag-o-poo pulling the caterpillars from their hosts towards extinction.

Bagworm Pellet-Like Frass Beneath Bags

Bagworm Pellet-Like Frass

The male and female caterpillars take very different paths as they develop. The adult female bagworms never develop into a moth-like insect. They remain inside their bags and develop into something that looks more worm-like than moth-like.

End-of-Season Closed Bags

Bagworm Pupae

The mature bagworm female moths have no wings, no apparent mouthparts, no antennae, and three pairs of very short, dysfunctional legs. Her abdomen terminates in an ovipositor (egg-laying structure) used for depositing and packing her eggs into her pupal case, which is her main function in life.

The mature females emit a chemical attractant (sex pheromone) that draws in the males, and mating occurs with the females remaining in their bags. Soon after mating, the female produces overwintering eggs that are laid snug inside of their mother's old bag. The females die once they produce their eggs. Each female is capable of producing 500 – 1,000 eggs, which explains why populations can build rapidly.

Dead Bagworm Female Filled with Eggs

Male bagworms develop into a fly-like moth, and they are capable fliers. Their pupae look much like other moth pupae, and they wiggle part of the way out of the potty hole to allow the male moths to emerge. Seeing the empty pupal skins means male moths are on the wing.

Bagworm Male with Its Pupal Skin

The males have large antennae used to detect and track the parfum de l’amour wafting from the female bags. Once found, the males mate with the bag-bound females.

Bagworm Male Mating with Female

Bagworm Management

1. Check Deciduous Hosts: Although common bagworms are sometimes called “evergreen bagworms," it's a common misconception that bagworms only eat evergreens. In fact, bagworms may feed on over 125 species of evergreen and deciduous woody plants in 45 plant families. Overlooking bagworms on deciduous trees and shrubs allows the plants to become reservoirs for infestations next season.

Bagworm on Sweetgum - Last Year’s Bag on Left and This Year’s Bag on Right

2. Look for “Hot Spots.” Since bagworm females never fly, evolution has imparted another method for bagworms to seek new horizons. When the overwintered eggs hatch in the spring, the 1st instars can spin a strand of silk from modified salivary glands to catch the wind and "balloon" to new locations. This dispersal behavior is one of the reasons bagworms may appear in landscapes on hosts that were not infested last season.

Bagworm “Ballooning” Silk

Coupled with the large number of eggs produced by the females, it’s also the reason we commonly find “hot spots” in landscapes with a high concentration of bagworms. It’s important to focus attention on the small bagworm hot spots to prevent them from becoming full-fledged conflagrations next year.

Developing Bagworm Infestation

Bagworms Moving Out of a “Hot Spot”

3. Don’t Be Fooled: As noted above, bagworm caterpillars anchor their bags to their hosts as they feed. However, the silk anchor also keeps dead caterpillars from falling to the ground. If insecticide applications have been made, it’s important to open a few bags to assess the efficacy of the applications. The infestation may have been eliminated, meaning nothing else needs to be done.

Bagworm Tied-Off While Feeding

4. Digital Control: If viable bagworms remain, the only effective control option is to pick off and destroy the bags, which will eliminate the females and later the overwintering eggs. This control method remains effective throughout the fall, winter, and spring. Bags should be destroyed rather than simply being dropped to the ground because eggs will still hatch from bags on the ground.

We have illustrated bagworm digital control in previous BYGL Alerts. It’s a highly effective and satisfying management tactic, and thus far, no bagworm populations have become resistant. The following images provide a refresher.

Digital Bagworm Management Tool

Digital Management – Step 1: Find Bagworms

Digital Management – Step 2: Pluck Bagworms

Digital Management – Step 3: Place on Hard Surface

Viewer Discretion Advised

Digital Management Step 4: Apply Compaction

Digital Management Step 5: Assess Efficacy

The Last Thing They Ever Saw…

Ron Wilson

In The Garden With Ron Wilson