Understanding Catalpa Worms and Parasitic Wasps

What Are Those White Egg-Like Structures on Catalpa Worms?

If you've spotted catalpa worms (also called catawba worms) on your catalpa tree with small white oval attachments, you're likely seeing the pupal cocoons of a parasitic wasp—not eggs. These tiny wasps are natural enemies of the catalpa sphinx caterpillar.

How the Parasitic Wasp Lifecycle Works

The female wasp deposits her eggs through the caterpillar's skin. Once hatched, the wasp larvae feed internally on the caterpillar's tissues. When fully developed, they exit the host and spin silken cocoons on the caterpillar's exterior—those white "egg-like" structures you see. An infected caterpillar never survives to adulthood.

Natural Biological Control

This parasitism is nature's way of keeping catalpa worm populations in check. Wasp numbers fluctuate significantly from year to year, so heavy infestations one season may be followed by almost none the next. There's no practical way to control the wasps, nor is it necessary—they provide valuable biological control.

What This Means for Your Tree

If you're raising catalpa worms for fishing bait, understand that parasitism is normal and unavoidable. The wasps pose no threat to humans, pets, or the tree itself. Next season's caterpillar population may be largely free of parasites.

Reference: Auburn University Entomology - Catalpa Sphinx