The elegant Anise Swallowtail (Papilio zelicaon) is often mistaken for the Eastern Black Swallowtail (Papilio polyxenes) here in Southern California. The caterpillars look so much alike that this is probably one of the reasons the mistake occurs. Basically, this is the 'west coast' version of the Black Swallowtail. Both oviposit (lay eggs) on plants in the Apiaceae family which include Parsley, Fennel, and Dill. Sometimes, you may find eggs on plants in the Rutaceae family (citrus), which happened recently to me when I spotted two little babies on Valencia Orange tree leaves. I've also found eggs on my Rue (Ruta graveolens) herb. So, you see? They are a fairly adaptable species!
In the Orange County, California area, the Anise Swallowtail (herein, will be referred to as AST) has had a rather interesting history. When the county was still undeveloped and much of the land was more wild fields of wildflowers and grasses, Fennel was abundant and the AST could be found fluttering about. 
Then, as land developers came in, taking over the fields and laying a concrete jungle, much like the fate of the royal Monarch butterflies with their host plant Milkweed (Asclepias spp.)), fewer Fennel plants became available. Fewer and fewer ASTs were soon seen. Many of these butterflies went into diapause, and some records indicate this 'overwintering' time went as long as up to seven years! (My personal experience: 14 months as the longest time my AST pupae stayed in diapause.) As gardeners began planting herbs such as Parsley and Rue and fields were being 'saved' or returned as wildlife parks, etc. we began to see a resurgence of these beauties.
Now, thank goodness, an abundance of Fennel (Foeniculum vulgare) is now found in park reserves and along many roadsides in California, so the Anise Swallowtail is BACK! Just check this perennial (meaning, it grows all year long) to see if you can spot any of the spherical eggs of the AST…
It is often at the later instar that people often mistake the AST for a Monarch. Why do you think this is? (most likely because of the green and black colouration)
A hint to remember: A good indicator of what type of butterfly/caterpillar you have is to note what the caterpillar is eating. If the larva is eating Parsley, then it is NOT going to be a Monarch!Note: Anise Swallowtails and Black Swallowtails also will eat Rue, Dill, Fennel, Citrus leaves,…
The Swallowtail butterflies do a rather interesting thing before they go off to pupate. This makes it easy to determine when they plan on pupating for those who are hand-raising them. What is the 'hint?' Ahhhh…it is simple. They do a gut-purging poop that is the most disgusting thing ever! It is almost like a diarrhea; runny, gooey, smelly…yep, it is like they've taken an enema or something. Once this is observed, the larva won't be eating any longer but will search for a place to pupate. Swallowtails make a silken harness or sling and hang head UP (no 'J' for them) when pupating.
The Anise Swallowtail pupa can be brown or green. There are often discussions and even controversies as to whether a Black or Anise Swallowtail's pupa will be green or brown depends solely on what it pupates against. NOT true! I have had brown pupa against green backgrounds and green against brown backgrounds and everything in between. So, that idea is out-the-door.
While in the pupa stage and undergoing metamorphosis, this butterfly may decide to 'hang out' and be in diapause for awhile. So, don't worry if you don't have an adult eclose in two weeks, or two months, or even ten months! It does not mean your pupa is dead! Don't squeeze it or anything either.
Just give it time…Good things come to those who wait. One day, you will have a glorious butterfly fluttering about your garden. These butterflies are just spectacular and all the waiting will be worthwhile.
