Anise Swallowtail (Papilio zelicaon)


The elegant Anise Swallowtail (Papilio zelicaon) is often mistaken for the Eastern Black Swallowtail (Papilio polyxenes) here in Southern California. The caterpillars look nearly identical! The adults definitely have differences in markings, that, when compared side-by-side, are evident. But, whether you live on the east OR west coast of the United States, the information contained here on this page will be helpful since both species share much of the same general qualities.

The Papilio zelicaon is a member of the Papilionidae family. This medium- to large-sized butterfly has a wingspan of 3” to 4.25” and can often be seen fluttering about beginning in April. The females oviposit (lay eggs) on plants in the Apiaceae family which include Parsley, Fennel, and Dill. You may also find eggs on plants in the Rutaceae family (citrus), such as Valencia Orange trees and the herb Rue (Ruta graveolens). Creamy-beige, pearl-like spherical eggs are laid singly on the tops of leaves. This picture shows an egg on Fennel. If you have an orange or lemon tree, you will often find the eggs at the tips of the newer leaves.

Soon, after about the fourth day, you will begin to see changes in the egg’s  colo
ur. The top begins to darken. This will be the caterpillar's head.

Note: Temperature can effect the length of time it takes for a caterpillar to hatch from the egg.

As soon as it hatches, the 1st instar (first larval stage) turns around and eats its own eggshell!

The first two instars of the Anise Swallowtail look NOTHING like the later instars. The BGEditor likens this instar to ‘Oreo cookies’ because they have an AB pattern of black-white-black, just like an Oreo! During each molt (shedding of the old skin, as it is outgrown), the caterpillar will stop eating for quite some time, go off to a quiet spot, then undulate to shed the outgrown skin.

Now, during the time a caterpillar molts, it is impo
rtant to remember a few things: it becomes very still, it doesn’t eat, and it should be bothered! Lots of times, people will think, “My caterpillar is dead! It isn’t moving!” It’s just getting ready to molt. Now, remember when the little one first hatched that the first thing it ate was the how the chorion (eggshell)? Each time it sheds it old skin it will turn around and eat the shed skin (exuvia)! Here is the little one eatings its exuvia.

By the 3rd instar, a distinct change in colour is taking place. Gone is that Oreo cookie look. More and more white is showing and the orange is more noticeable as well. By the time the little one has shed this skin, it will look like a totally different caterpillar—in fact, the 4th instar is often when people mistake the Anise Swallowtail for a Monarch. Can you guess why?

In this picture, you can see three different instars of the Anise Swallowtail. On the far left, you can see the earlier instar. In the front, it is still showing more of the black, but the one to the far right is green! They don’t even look like they’d be related, do they?

That green caterpillar looks awfully familiar doesn’t it? This is the one that is often photographed and used in children’s books when a photo of a caterpillar is needed. The colouring is also what causes most people to mistake it for a Monarch! How can you tell the difference? The easiest way? What is it eating? Monarchs eat Milkweed. Anise and Black Swallowtails eat plants like Parsley, Fennel, Rue, …So, if you find a green caterpillar on your Parsley? More than likely it is NOT a Monarch!

As it nears the end of the larval stage, the caterpillar becomes incredibly plump. Look at the size of this Anise Swallowtail munching on some Parsley…note how it looks like the ‘skin’ is stretched tight like a sausage.

When it is time to pupate, like other swallowtails the Anise Swallowtail will ‘purge’ and a nasty blast of ‘loose stool’ will be expelled. This will be the hint that your little one is going to be taking off to find a resting spot for undergoing metamorphosis and the final stage of its life-cycle.

Caterpillars will rarely pupate on the host plant but will often travel quite some distance away. The Papilio zelicaon will make a silken sling/harness and pupate head UP, usually on a stick or branch.

The pupa for this particular species can be green or brown. (and there is no rhyme or reason as to why the pupa is brown or green…it doesn’t matter WHAT the caterpillar was next to!)

So, don’t be surprised if you end up with a green chrysalis or a brown one and both eggs were from the same female. Another interesting thing is that, like most swallowtails, there is NO guarantee that the butterfly will eclose in about two weeks. Sometimes, they will go into diapause (overwinter) and may remain  as pupae for MONTHS! Be patient; eventually, a butterfly will eclose.


History of the Anise Swallowtail in Orange County, California

Orange County, California is south of Los Angeles and north of San Diego. The county borders the Pacific Ocean on one side and includes the Santa Ana Mountains and canyons. When the county was still undeveloped and much of the land was wild fields of wildflowers and grasses, Fennel (Foeniculum vulgare) was abundant and the Papilio zelicaon could be seen in abundance, fluttering about. Here is a female nectaring on some Fennel blossoms.

As land developers came in, taking over the fields and laying the great concrete jungle, much like the fate of the royal Monarch butterflies, the Fennel plants were trampled and bulldozed. Soon, fewer and fewer Anise Swallowtails were seen.

Many of these butterflies went into diapause, and county records indicate this 'overwintering' time went on as long as up to seven years!  As gardeners began planting herbs such as Parsley and Rue and fields were being 'saved' or returned as wildlife parks, etc. there was a resurgence of the butterflies, once again.

There is now an abundance of Fennel growing in park reserves and along many roadsides throughout Orange County, including on the island of Catalina in California, so the Anise Swallowtail is BACK!

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