If you've noticed your box plants looking ragged or stripped bare, there's a good chance box tree caterpillars have moved in. These small but voracious pests can cause serious damage in a surprisingly short time. Understanding exactly what they eat—and how they feed—is the first step toward protecting your garden.
What Do Box Tree Caterpillars Eat?
Box tree caterpillars (Cydalima perspectalis) feed almost exclusively on the leaves and shoots of box plants (Buxus spp.). Their preferred hosts include common box (Buxus sempervirens), as well as other cultivated varieties such as Buxus microphylla and Buxus sinica. In heavy infestations, they may also nibble on young stems, though foliage remains their primary target.
How They Feed
These caterpillars don't just chew from the edges inward. They often start by skeletonizing leaves—eating the soft tissue between the veins—before moving on to consume entire leaves. Young larvae may begin by grazing on the upper leaf surface, while older caterpillars are capable of stripping whole shoots down to bare stems. This feeding pattern is what gives infested plants their characteristic "bald" or "ghosted" appearance.
Why Box Plants Are Their Only Food Source
Box tree caterpillars are specialists. Unlike many moth larvae that can switch between host plants, Cydalima perspectalis has evolved to rely on Buxus species. The chemical makeup of box leaves—particularly their alkaloids—actually helps the caterpillars defend themselves against predators. In other words, eating box isn't just a preference; it's a survival strategy.
What Happens When Food Runs Out?
When a box plant is completely defoliated, the caterpillars don't adapt by switching to other garden plants. Instead, they either migrate to nearby box specimens or starve. This is why infestations often spread in a pattern—moving from one box hedge or topiary to the next, leaving a trail of destruction behind them.
Signs Your Box Plants Are Being Eaten
Before you see the caterpillars themselves, there are telltale signs that feeding is underway:
- Webbing or silk threads on leaves and stems
- Chewed or skeletonized foliage
- Greenish-yellow frass (droppings) on leaves
- Bare patches appearing suddenly on otherwise healthy plants
- Small green caterpillars with black heads, often hidden inside the plant
Seasonal Feeding Patterns
Box tree caterpillars are most active from spring through autumn, with peak feeding occurring in late spring and again in late summer. In warmer climates or mild winters, they may continue feeding almost year-round. Each generation can strip a plant significantly, and multiple generations per year mean the damage compounds quickly.
Protecting Your Box Plants
Because these caterpillars are so specialized, targeted control methods work best. Pheromone traps can help monitor adult moth activity, while biological controls like Bacillus thuringiensis (Bt) are effective against young larvae. For smaller plantings, hand-picking caterpillars and removing webbed sections remains one of the most reliable approaches. The key is early detection—once feeding is visible, act fast, because these pests don't slow down.
