Look Out for Black Swallowtail Larvae in the Fall Herb Garden

by Matthew Orwat | Oct 21, 2013

Second instar, Black Swallowtail larva. Image Credit Matthew orwat

Busily devouring dill and fennel, the lime green, black striped caterpillars in the UF IFAS Extension Washington County Office have quickly become a popular attraction.  It is fortunate that the South’s climate is warm enough to allow for three generations of this species every year.

Larvae Busily Devouring Dill. Image Credit Matthew Orwat

 Soon, the caterpillars of the Black Swallowtail (Papilio polyxenes asterius ) butterfly species will continue their pupae stage by forming a chrysalis and emerging as one of Florida’s most recognized swallowtail butterflies. 

The chrysalis is formed by two glands located inside the caterpillar that secrete silk.  The silk threads stick together and harden when exposed to fresh air.  The hard, protective coating is usually camouflaged from predators and blends in with the environment.  Inside the chrysalis, the process of metamorphosis continues as the adult structure forms while the juvenile structure breaks down.  The insects are very inactive during this time as they grow and change.  This stage can last from two weeks to an entire season in temperate climates and tropical dry seasons.  When hormones indicate it’s ready, the butterfly emerges by splitting the chrysalis open either biting its way out or using spit to soften the ends.

Green Chrysalis. Image Credit Don Hall UF IFAS

The Black swallowtail has quite a heavy appetite for such a small creature.  They eat a variety of plants in the carrot family (Apiaceae) such as dill, fennel,  parsley, celery, and carrot leaf. In addition to these cultivated species, they will feast on mock bishopweed, roughfruit scaleseed, spotted water hemlock, water cowbane, and wedgeleaf eryngo. They have also been known to enjoy Common Rue (Ruta graveolens L.).

They exhibit several interesting behaviors throughout their life cycle. For example, when they feel threatened the Black Swallowtail larvae will exhibit yellow antennae-like structures called osmeterium. These flare out and emit a foul odor, like rotten cheese, if one’s finger gets too close.

Osmeterium on display. Image Credit Matthew Orwat

Even though they are voracious plant eaters and honorable defenders of their territory, butterflies play a vital role in agriculture by pollinating crops and flowers.  They’re an indicator of a healthy ecosystem; an abundance and diversity of butterfly species illustrate the overall health of an area.  With their acute sensitivity to contaminants and toxins, butterfly populations will not be found in polluted areas.  Recognized for their beauty, butterfly watching has also become a popular hobby and pastime. 

Photo courtesy of Donald Hall, University of Florida.

It’s never too early to think about planning a butterfly garden.  For more information on creating a backyard butterfly habitat, download this 4-H fact sheet for kids and parents.   For more information on this specific butterfly, visit the UF IFAS EDIS website for a publication on the Eastern Black Swallwtail.

Additional Content by:

Julie Pigott Dillard, Director, UF IFAS Extension Washington County