Papilio xuthus

Papilio xuthus is a butterfly in the swallowtail family, commonly found in Asia (its common name is the Asian Swallowtail), but also found in Hawaii. There is some debate as to how it got there, whether it was introduced by accident, on purpose, or made it there all on its own. Most believe it was introduced accidentally. This species was first observed on Oahu in April 1971 and then on Maui in May 1974. Today, it can be found on all the major Hawaiian islands. It can be found in all stages of development year round in Hawaii, as there is essentially no winter. Winter in Hawaii is characterized by shorter day length, but even so the temperature is usually in the mid 20's Celsius - not exactly frigid.

This caterpillars of this species feed on citrus and related plants (family Rutaceae). I recently raised 3 eggs on Citrus x limon (lemon) and Citrus x sinensis (sweet orange).

This little yellow sphere is the egg of this species. It's tiny, about 1 mm in diameter, but they're not hard to find if you know what you're looking for. Against the green background of this citrus tree on Kaua'i, it stands out. This egg was found on November 22, 2012. The eggs can be laid on the top or underside of leaves, but usually near the edge of the leaf.

At the center of this photo, you can see an egg, except it's not yellow anymore, but a translucent white. That's because the caterpillar has hatched and is gone! Usually, once the larvae hatch, the first thing they do is eat their old eggshell - it's a hearty first meal. However, sometimes for whatever reason they don't, or perhaps they were eaten by predators before they could get around to eating the eggshell. At this small stage, their main predators are spiders, ants, and the like.

In the center of this photo, I've captured a 1st instar caterpillar in the process of hatching. Half its body is out of the shell, and the other half isn't. Caterpillars moult several times after hatching, before becoming a pupa (aka chrysalis) and finally a butterfly. Most moult 5 times, but this number is variable depending on the species. The stage between moults is known as an instar. Thus, after hatching and before it has moulted for the first time, the larva is in its 1st intar. The plant you see in the picture is a lemon tree seedling.

This photo shows two newly hatched 1st instar larvae. The little guy on the left is eating his eggshell. The one on the right has just hatched moments ago, and is taking a rest, but eventually it will eat its eggshell too. This behavior is not uncommon amongst butterflies. These larvae are about 2 mm after they hatch. It sounds small, but considering how small the egg is, I'm surprised they are as big as they are.

After about 3 days of eating, they've doubled their length (which means they've increased their volume by a factor of 8) and are a huge 4 mm! They then moult. The one on the left has just done so, and the little round black thing you see in front of it is the old head capsule it had to shed along with its skin. It is now a second instar caterpillar. You can see the chew marks on the lemon leaf. It doesn't seem like they eat a lot now, but wait until they're in their 5th instar, 3 caterpillars can defoliate a small seeding a couple of feet high. The larvae are essentially just eating machines. It's basically all they do. Avoid predators, eat, rest, poo, repeat as needed until they get to a big enough size that they need to moult again. Sounds like a pretty good life if you ask me....well, except for the predators part in the wild. In my home though, they have no natural predators, and so yeah, it's pretty sweet. This is what retirement must be like.....

This is what a 3rd instar caterpillar looks like. The coloration has changed a bit, and it's about 9 mm in length now. By the way, the caterpillar looks this way because it's trying to look like a bit of bird dropping, and it's one of the strategies it uses to avoid predators. Despite this, only about 1% of the eggs laid in the wild survive to become adult butterflies.

After some more eating and growing, it's ready to moult again into the 4th instar. It stops eating for about a day in order to prepare, and will lay down a small mat of silk to support itself. Then underneath the current skin and head, it will grow a new head and skin, and once it's ready, it will literally crawl out of the old one. In this picture above, you can see a bit of a bump behind the black head capsule. That is the new head developing underneath.

The 4th instar caterpillar is about 1.5 cm long. Doesn't look much different than before, but just a bit bigger. It's still trying to pass itself off as a large bird dropping to avoid predators.

Alright, now this is the best part. This is the final stage, or 5th instar, and instead of a bird dropping lookalike, the caterpillar has transformed into this marvelous green creature with spots and stripes and fake eyes behind its real head capsule. Pretty cool right? This is where it will do most of the growing, and a caterpillar will defoliate a small branch of probably a dozen mid sized leaves.

The larva eats and eats, and is now fairly big. You can see the change by comparing the length of the caterpillar to the size of the head, which doesn't grow along with the rest of the body. You can see that it's a lot larger now than in the preceding picture.

It will ultimately grow to just over 4 cm when mature. Then, it will pupate, which is a really amazing process.

Here's a group shot of all 3 of them when they made it to the 5th instar. Even though they all hatched within a few hours of each other, as they grew, some obviously grew faster than others. The size differences are pretty evident in the group shot.

Before it gets ready to pupate, it will stop eating and clear its guts of whatever is left in there. Usually this is a slightly loose bit of stool (the technically term for caterpillar poop is frass). In some species, this last poop will be totally watery, but in this species, it's semi-solid. After that, it will wander around several hours looking for a place that it thinks is a good pupation site. The caterpillar will then lay down a mat of silk, which you can see on the twig in the picture above. At one end of this mat, it will spin a raised bump of silk, to which it will attach its anal prolegs (basically its bum). At the other end, it will spin a thin but strong silk girdle, and it will slide itself through it.

As it's getting ready to pupate, the various tissues inside the body of the caterpillar start to break down, for they have to re-organize themselves in order to form the adult butterfly. As this happens, the legs are no longer legs, and can't hold on to the branch any more, as shown above. It stays attached to the twig by its anal prolegs anchored to the silk pad, and at the front, it's supported by its silk girdle, which is barely visible in this picture.

After about 24 hours, it sheds its skin, which is really cool to watch. I have it on video, but it's too big to load, and I don't have any sequential pictures for this species to show the process. I do have it for other species, so stay tuned. Anyway, this is what the pupa looks like for this species. You can more clearly see the silk girdle I mentioned earlier that's supporting the mid portion of the pupa. It's a pretty good camouflage amongst the leaves and twigs. The new pupa is really soft, and it takes about another 24 hours for the outer casing to harder. During this time, they're pretty fragile and it's probably best not to poke and prod them too much.

Eventually, all 3 of the eggs I found successfully transformed into pupa. I had 5 lemon seedlings about 20 cm tall, all of which were complete decimated. They had zero leaves left. I suspect some will die, but a couple of the seedlings are starting to recover and grow new leaves. I also had a two year old orange tree that was probably 3 feet tall. It lost about half its leaves. Next time, I'll be better prepared!! So right now, all three pupae are sitting beside me on my laptop table, and one is nearly ready to emerge as a butterfly. It will happen some time today. I'll post more pictures as soon as I can!