Photo: Catalpa Sphinx Moth Caterpillars, Judy Gallagher
Judy Gallagher is an ASNV board member and a regular surveyor of local wildlife who also captures photos of what she sees, in particular the less common species. Here are some observations from her most recent survey.
Sometimes I notice an insect because it is big and colorful. With its shiny black body marked with yellow and white, the two-inch long Catalpa Sphinx Moth caterpillar stands out against its background.
Judy Gallagher
Like many plants, the Catalpa Tree produces a toxin that makes it taste bad, and this protects the tree from most plant-eating organisms. The Catalpa Sphinx Moth caterpillar has evolved to be able to digest and process this toxin, which makes the caterpillar unpalatable to birds and most other vertebrates. Its bright colors are a warning "Don't eat me, I'm toxic". The caterpillars eat constantly and can nearly defoliate the Catalpa Tree. Fortunately, the tree can produce multiple sets of leaves in a year and is rarely seriously damaged. The Catalpa Sphinx caterpillars only feed on Catalpa, so it's not in their best interest to have the tree die.
Judy Gallagher
But if the tree senses that it is being harmed too much, it produces extra-floral nectaries on its leaves. This is just like having a flower with nectar, minus the flower. The nectar from the extra-floral nectaries attracts wasps and other insects. In this case, a parasitic Braconid Wasp, attracted by the nectar, has laid eggs beneath the skin of the Catalpa Sphinx Moth caterpillar, and the developing wasp larvae feed on the caterpillar. This will eventually kill the caterpillar, but not until the wasps are ready to pupate. So, the tree attracts wasps, which parasitize some caterpillars, keeping the caterpillar population enough under control that the tree is not damaged too much. Nature's balance is quite remarkable!
Judy Gallagher
Caterpillars that survive will climb down the tree into leaf litter where they will eventually pupate and transform into the adult moth. The adult Catalpa Sphinx Moth is a dull brown, not showy like the caterpillar.
Judy Gallagher
It's worth mentioning that although both Northern and Southern Catalpa trees are native to North America, neither is native to Northern Virginia. So why are the trees found here? The answer is that the Catalpa Sphinx Moth caterpillar, while toxic to most vertebrates, is really good fish bait. Many Catalpa Trees outside their narrow native range were planted by fishermen to ensure they would have their favorite bait nearby.
View all of Judy’s Observations from Meadowood articles here.