Inchworm Invasion: Identifying and Controlling Cankerworms Naturally

What They Are

Small (½ inch), thin green worms hanging on silk threads are likely inchworms (cankerworms or loopers). They appear in large numbers, covering yards and people.

Effective Biological Control

Bacillus thuringiensis (Bt) is a bacterium that produces a toxin lethal to these caterpillars. It must be applied while larvae are actively feeding (usually spring). Once they seek underground pupation sites, Bt is ineffective.

Timing Is Critical

Apply Bt as soon as you see active feeding. In northern latitudes, this is typically May–June; earlier in southern climates. Multiple applications may be needed.