Hi - could you help me identify this caterpillar? It was on my lime tree. I’m in Yamaguchi-ken.

Hello!

Thanks for your submission!

You’ve found my all-time favorite bug of Japan and the one on my header image, a Papilio xuthus , Chinese Yellow Swallowtail (called “Ageha” or “Nami-ageha”).

You can see other posts I’ve made about these iconic and beautiful butterflies on my blog here: https://bugsofjapan.tumblr.com/tagged/papilio_xuthus



This particular caterpillar is going to be a pupa within 5-10 days depending on the weather temperature. It’s nearly impossible to tell the sex of a caterpillar, but I had a system I was working on when raising these, judging by the shape of the abdomen when they were fully grown as caterpillars before they became a chrysalis– however yours is not very far into his fifth “instar” (shed skin stage as a larva) judging by the size of his face (large) to his body (kind of small and wrinkly). He will get QUITE a bit bigger, probably as big as your pinky finger before becoming a chrysalis!



The caterpillars of Papilio xuthus can ONLY feed on plants in the citrus family (including Rue), but Japan is chock-full of citrus trees so they are commonly seen in suburban areas. They will eat a LOT of leaves at this stage, but they are a caterpillar for only 5-10 more days before becoming a butterfly, and then going on to be a wonderful pollinator in the neighborhood. Your caterpillar, if he grows up, will live as a butterfly all the way until the first frost when he will freeze and die. However, any of his children that have become a pupa will stay as a pupa over winter, even in freezing temperatures, and emerge in the spring time as the first ‘flight’ of Ageha in April.