Spicebush Swallowtail Caterpillar

I can’t help but smile when­ev­er I see a spice­bush swal­low­tail cater­pil­lar. This cater­pil­lar is in its fifth stage of life, called the fifth instar. 

Its car­toon­ish look has a big­ger pur­pose than amus­ing me. The eye­spots have false “pupils” that bulge and even have white in them that gives the impres­sion of light reflect­ing from them. The “mouth” is also false. This adap­tive col­oration mim­ics the head of a green snake and is meant to dis­cour­age birds and oth­er preda­tors from try­ing to eat it. Should a bird still pick it up, the cater­pil­lar emits a type of chem­i­cal repel­lent to dis­suade it from mak­ing it a meal. 

One oth­er line of defense dur­ing the fifth instar is that the cater­pil­lar will lay down a silk mat on the top of a leaf, which caus­es the leaf to fold over on itself, leav­ing the cater­pil­lar in-between the two halves. The cater­pil­lar will usu­al­ly stay there dur­ing the day and emerge from its leaf pro­tec­tion to feed at night.

The spice­bush swal­low­tail is found through­out the east­ern U.S. Its host plants in our area include the spice­bush and sassafras.