Field Identification
Black swallowtail larvae—green with black bands and yellow-orange ‘horns’ that pop out like party favors when disturbed. They munch carrot, parsley, dill, and fennel foliage; one or two plants worth of damage beats zero pollinators later.
Early instars resemble bird droppings; later instars smooth out and show transverse bands. Chrysalises hang by silk girdles on stems or fence posts.
How to Deal With It
Organic Control Methods
Usually unnecessary—if you must, Bacillus thuringiensis kurstaki spot-sprays only the individuals you refuse to share with; avoid blanket sprays that nuke beneficials.
Parasitic wasps (e.g., Cotesia congregata) form silk cocoons on surviving caterpillars—leave those mummies; birds and spiders take stragglers.
Plant extra dill or fennel as sacrificial hosts; accept cosmetic herb damage; stagger parsley blocks so one patch feeds larvae while another stays pristine.
Hand pick and relocate to a dedicated ‘butterfly hedge’ if aesthetics demand zero holes.
Scout umbels in late summer; educate household members so caterpillars are not mistaken for ‘green demons.’
Let Nature Handle It
Natural Enemies
- Cotesia congregata
- Birds
- Spiders
Threat Map