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Wild Thing : Bag of Worms

That’s not a pine cone hanging from your evergreen.

By Sheryl Smith-Rodgers

So those twiggy "pine cones" hanging from your tree’s branches look right at home, right? Harmless, too. That’ll change in spring when evergreen bagworms hatch and disperse, possibly triggering an infestation.

Though dubbed a worm, Thyridopteryx ephemeraeformis begin life as moth larvae. After overwintering as eggs inside their two-inch-long cone, the caterpillars scoot off in search of food. Many balloon away on a strand of silk.

Here’s where the species turns weird. Newbie bagworms — barely 1/25 inch in length — use silk to attach sand-like fecal pellets around their body, creating a mini bag. Through a top opening, the caterpillar, like a snail, sticks out its head and front legs for mobility.

When threatened, it pulls back into the bag and shuts the opening. As the larva eats and grows, it layers leaf debris like shingles around the bag. By late summer, the inch-long larva stops eating and pupates within the cone.

Males emerge as fuzzy black moths with clear wings. Not females. Within their bags, they pupate into egg-making machines that lack eyes, mouths or legs. Attractive, eh? Males think so, once they locate a female via her sexy pheromones (chemical signals). After mating, a female deposits up to 1,000 eggs within the bag, then dies. The twiggy cone remains in place through winter, unless someone like you — fearing an infestation — decides it’s not so at home there!

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