Tuesday, July 13, 2021

Evergreen bagworm – I carry my home on my back

An evergreen bagworm 'bag' hidden in a juniper tree.Two bagworms try to escape.Three bagworms try to escape.An evergreen bagworm explores the edge of a plastic container.
Left: An evergreen bagworm 'bag' hidden in a juniper tree. Center left: Two bagworms try to escape. Center right: Three bagworms try to escape. Right: An evergreen bagworm explores the edge of a plastic container.

On a recent visit to Oklahoma, we became interested in the evergreen bagworm (Thyridopteryx ephemeraeformis). Our Sooner family is at war with these insects because of the damage they can cause to trees. We got drawn into the battle, first by picking larvae out of the infected trees and squishing them, and then studying them and understanding their lifecycle.

The bagworms we studied were in Rocky Mountain juniper (Juniperus scopulorum) trees. The larvae ingeniously camouflaged their bags in way that you might say is artful. They spin their bags in their larval life, decorating it with bits of plant material from the trees on which they feed. In the case of junipers, juniper needles and berries are attached to the bags.

Given the time of the year, we are seeing (in these photos) larvae, which are brown/tan caterpillar with black markings. Larvae remain in their protective bag, sticking their head out to feed. The larvae will feed up until late August and then pupate. The males become moths. The females never grow wings and never leave their bags.

We plucked a few larvae and put them in the bottom half of a plastic bottle and covered the top with saran wrap and rubber band. When handling the bags, the larvae retract inside and close off the bag opening. Little by little if left alone, they start to come out. If you put them somewhere where they don't want to be, they move. When they do, they drag their bag behind them. They carry their house and possessions with them.

The larvae must do that naturally in an infected tree to reach different food sources and only attach for good to pupate. To test that, we should have put a marker on a bag and see if it moved around the tree day by day. Unfortunately, we didn't.

The specimens in our plastic trap never one went over the edge, but kept circling around the top. A pretty bag in tow and nowhere to go.

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