Spicebush swallowtail caterpillar

My colleague David Johnson’s Field Investigations in Biology class found this caterpillar on one of their forays into the woods. The animal was discovered hitching a ride on a student’s boot and was brought back to campus for the admiring crowds. I kidnapped it (the caterpillar, not the boot) for a photo shoot.

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This caterpillar does a fabulous impression of an outrageously colorful snake. Note the light “reflection spots” within each “eye.” When distressed, the caterpillar will apparently inflate its head and rear up. I poked it a little, but could get no response. I did not feel like tearing at its skin like a real predator (my inner blue jay would not come to the surface), so the snake-charming will have to wait for another day.

Spicebush swallowtail caterpillars spend their first few instars (“life stages”) looking like bird droppings. This allows them to loiter in plain view and they generally sit on the upper surface of leaves. Their last instar is the snake-mimic. At this stage they roll leaves into loose cigars and hide inside the bore of the roll. Their snaky heads face outward.

The caterpillar will shortly turn into a crusty brown pupa from which the adult butterfly will emerge in the spring. Sewanee has plenty of the species’ two host-plants — spicebush and sassafras — so this species is quite abundant, but the spectacular caterpillar is surprisingly hard to find.

6 thoughts on “Spicebush swallowtail caterpillar

  1. manayunkia

    It was fantastic serendipity. The students were sitting on a fallen tree as I discussed the the value of light gaps in a forest community when this guy was spotted on the boot of a student. I suspect the caterpillar was keen on hearing the lecture too. It is Field Investigations after all.

    ~David J.

    1. David George Haskell Post author

      I’m pretty sure that spicebush swallowtails are just in the eastern part of N America. However, there are dozens of other species in the same genus, many of which are in S America, so it is likely that you saw a caterpillar of one of those. They are impressive creatures.


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