We have yet another series of photographs to show the differences between the two species. First, the Papilio polyxens asterius​:

​Here is P. zelicaon:

And here together:

Although the P. zelicaon​ larva in these photos is a nice light form, even the darker forms have the same distinct differences including the huge color spots and bulkier shape. The P. zelicaon are much more cryptic on the flowers than the P. polyxenes asterius in these photos and the P. zelicaon seem much more comfortable on it in terms of their behavior. However, after offering the P. polyxenes asterius some flowers, they eventually did also eat them. 

Rearing notes for anise swallowtail (Papilio zelicaon) fifth instar larvae obtained as eggs or larvae in Albany, El Cerrito, and Berkeley California.

Rearing notes 7/12/17-7/24/17:

Here we compare the fourth and fifth instar larvae of the black swallowtail (Papilio polyxenes asterius), anise swallowtail (Papilio zelicaon) and a ♀ Papilio ​polyxenes asterius × ♂ Papilio zelicaon hybrid cross.

The hybrid larvae are still behind, so there quite aren't any fifth instars yet. However, we still took some more photographs of the fourth instar compared to the two pure crosses.

​The hybrids are truly perfect intermediates, no matter if they are dark or light forms. They share the same bulgy, shiny appearance as Papilio zelicaon, but aren't quite as spiky. The light forms seem to be patterned similar P. polyxenes asterius in the amount of white they have but still have thicker black bands than the pure breed and have broken saddles. Both the dark and light forms have smaller spots than Papilio zelicaon like P. polyxenes asterius. A good way to look at it overall is that the P. zelicaon are messy, the P. polyxenes asterius are smooth and clean, and the hybrid are just in between.

There are lots of fifth instar P. polyxenes asterius now, and they look distinctly different than P. zelicaon fifth instars. The P. polyxenes asterius still have much smaller and more circular spots such that they don't break the black bands and the spots on the thick thoracic band of P. zelicaon are still mostly absent. Because of this, they actually look blacker than P. zelicaon despite all being much lighter in the fourth instar. The greenish white bands seems to be to be much more even, at least for now, without any blue bands mixed in between that are common in P. zelicaon. The shape of the P. polyxenes asterius resembles tigers much more than P. zelicaon​ because they are so long and skinny with very large thoraxes; P. zelicaon tend to be slightly more bulgy between segments. Overall, the P. zelicaon are much more cryptic on flowers than the P. polyxenes asterius may seriously reflect on the different climates that they come from and what they feed on. In fact, we have put in some flower for the P. polyxenes asterius to see if they will feed on it and so far they have not. 

As for size, it now seems that the P. polyxenes asterius might actually have a chance to get bigger. They certainly look larger in the photos, but it is unknown just how much they have fed already. In the fourth instar, the P. polyxenes asterius seemed just slightly smaller with most at o.3 whereas 0.4 dominates P. zelicaon based on previous rearings. Very surprisingly, we now have a single 0.5 g P. polyxenes asterius which is the rare maximum for P. zelicaon, so there is clearly a lot of variation. But no matter what they are in the fourth instar, the fifth instar is the bulk of the growing so anything could happen. . .

Now that our hybrid ♀ Papilio ​polyxenes asterius × ♂ P. zelicaon larvae have molted to fourth instar, we can compare them with the pure breeds. As before, the hybrid seems like a pretty good intermediate. The fourth instars are light forms like P. polyxenes asterius and look almost identical except for a few minor differences. The black stripes on the saddle are not quite complete, unlike P. polyxenes asterius, but are also not as broken as light form P. zelicaon; the black stripes are also slightly thicker than P. polyxenes asterius in general. The tubercles of the hybrid seem also to be intermediate between the two species. Like P. polyxenes asterius, there are no spots on the thick thoracic stripe close to the head. This all seems to be pretty compelling evidence that the color form is a genetic trait and not just environmental.

On 7/23, a few more hybrid larvae molted to fourth instar and are of a darker form than the first one. Compared to P. zelicaon dark forms, they have more distinct white stripes between the segments and some have a more solid looking saddle like third instar P. polyxenes asterius​ third instars. 

Comparing the fourth instars of the pure breeds again now that they have reached the end of the instar, we see that the P. polyxenes asterius is still much smaller and less thick. The tubercles are much reduced in proportion to the body in the P. poyxenes asterius, making them look much like fifth instar P. zelicaon. Surprisingly, they are not actually very green despite being light forms. The spots of the P. polyxenes asterius are very small, which goes well with the very fine and complete  black bands, and are invariably yellow. In P. zelicaon, orange seems to be more common in the fourth instar and, according to some sources is a genetically determined dominant trait. For some reason, the P. polyxenes asterius also seems to have a slightly more thickened thorax, giving it a more tiger-like larval shape. 

Here we compare the third and fourth instar larvae of the black swallowtail (Papilio polyxenes asterius), anise swallowtail (Papilio zelicaon) and a ♀ Papilio ​polyxenes asterius × ♂ Papilio zelicaon hybrid cross. 

Now that we have mature third instar larvae of all three types of larvae, we decided to compare them side by side. The major difference between Papilio polyxenes asterius and P. zelicaon third instars is the amount of white. The latter always has a checkered white saddle and has minimal white dots along the body, especially near the rear. The P. polyxenes asterius larvae have a more or less solid chunk of white on for the saddle where even the tubercles are white, allowing the faint yellow spots there to be more easily seen. Another obvious difference is the size; P. zelicaon is indisputably larger, which would make a lot of sense because they have much larger eggs that hatch into larger first instars. As for the hybrid larvae, it is intermediate in size between the two species (perhaps even as large as P. zelicaon since the individual in the picture isn't quite full grown) but has a pattern that matches much more closely to P. polyxenes asterius. Some of the spots at the rear are blacked out though. 

We don't quite have any fourth instar hybrid larvae yet, but we can compare the fourth instars of the pure breeds. The fourth instar P. polyxenes asterius larvae is a markedly different thing than the P. zelicaon. Like the third instar, the P. polyxenes asterius is much lighter (all of the fourth instars, reared indoors, we have so far are light whereas only a very small percentage of indoor reared fourth instar P. zelicaon are light), even lighter than the light form fourth instar P. zelicaon in the photographs. In fact, the P. polyxenes asterius could almost pass as a newly molted fifth instar P. zelicaon because the white saddle is completely gone. All of the black stripes there are complete and consistent, unlike P. zelicaon light form larvae, and the tubercles are extremely reduced. Another indisputable difference that could not possibly be from natural variation within the species are the dots on the thickest thoracic stripe right before the head. The P. polyxenes asterius larvae are completely lacking in them, a characteristic that is completely unique to the fifth instar in P. zelicaon. 

Pictures of pipevine swallowtail (Battus philenor hirsuta) and anise swallowtail (Papilio zelicaon).

Another very small pipevine swallowtail (Battus philenor hirsuta) emerged today, most likely from a late non-diapausing pupa. It was a female which we haven't had a chance to get any good photographs in the past. Unfortunately, pipevine swallowtails are probably some of the hardest things to get to stay still because of their weak legs. It fluttered about and eventually flew away after two poor shots. 

We also had several female anise swallowtails (Papilio zelicaon) emerge over days but have no males. We released three females today and after about half an hour we saw one of them come back, nectaring on some flowers. It eventually landed somewhere and we got a quick shot in. It is a very yellow individual -- almost orange in some cells -- typical of summer broods. 

​Authors
Brian Liang

Rearing notes for our black swallowtail (Papilio polyxenes asterius) and anise swallowtail (Papilio zelicaon) hybrid crosses obtained from Cleveland, Ohio and Albany, California, respectively. 

Rearing notes 7/5/17-7/14/17:

Today we learned just what a confused newly molted anise swallowtail (Papilio zelicaon)  larva can be capable of. . .

We have always noted that in insect species where cast off cuticle is routinely eaten, there is some sort of psychological change that occurs immediately after molting that prompts them to look for the skin, recognize that it is skin, and eat it. The behavior seems purely instinctive. We have found, with observational experimentation, that putting skins at the mouth of these newly molted insects creates an automatic response to feed on it. The skins need not be its own. 

Today, we were playing around with a newly molted anise swallowtail (Papilio zelicaon) fifth instar that had not yet eaten its skin. We carefully placed the skin at its mouth to prompt it to start feeding on it while it was still in the "skin-eating mode". After it finished the skin, we continued to place more skins left behind by a few of the other larvae that molted. As long as we kept putting more skin there, it continued to feed, thinking that it still had not finished. It appeared to like the stuff very much. . . it is probably quite nutritious. 

Eventually, after finishing its fourth skin, we got a sick idea to try to see if it would be also willing to feed on larvae. We had a lot of first instars on hand that we thought couldn't be much different than the skin that it was already eating. The main other constituents are blood, which is obviously edible (in fact, injured larvae instinctively look for the blood to try to drink it up), and gut which contains partially digested food matter and fluids (which disturbed larvae sometimes regurgitate and then drink back up) and is also edible. Both of these things should actually be in more easily digestible forms than eating leaves and would probably be more efficiently assimilated by the body. This and many other reasons are why cannibalism is so great among meat-eating organisms and why meat is more nutritionally viable than plant matter. 

We put the first instar onto a skin and got it to start eating the skin first. When it got to the first instar, the first instar started thrashing around violently as it was getting attacked and the fifth instar backed off. Eventually, however, it started biting through the first instar from its end (the head capsule is difficult to bite) and ate the whole thing happily. . . We're not sure if it even realized. After that, we gave it another one, along with a sixth skin, which is also ate. Perhaps it will have some strange poops after this meal. 

After the second first instar, it started to lose its appetite and we put it back onto the fennel. Obviously, it would not be a good idea to try to sustain it only on skins and larva and it would most likely reject them once it gets out of the skin-eating mode. But this was still an amusing (okay, maybe more disturbing than anything else) experiment. Perhaps this larva will perform better than it would have if it hadn't eaten all this stuff.

Now that we have both males and females of the two species, we decided to compare them side by side. The shapes of the bodies is surprisingly different. While the zelicaon female is extremely fat and stout with a fur smothered ball-like abdomen, the polyxenes female is more petite with a hairless, tube-like abdomen. Both females in the picture are no more than one day old and have not fed, so it should be a fair-enough comparison. It is also consistent between our other females not shown. Another clear difference is the shape of the wings. Polyxenes has slightly longer forewings compared to the hindwings, making it look just slightly more T-shaped which, coincidentally or not, is a characteristic of the model mimic, Battus philenor. Similarily, the tales of the polyxenes seem fatter and shorter like Battus philenor whereas the zelicaon's are long and skinny like tiger swallowtails. However, there does seem to be some variation in both of these traits, so it may be coincidental for these two individuals. 

In the males, there seems to be a similar trend. The zelicaon male's abdomen is much hairer than the polyxenes'. Although the zelicaon male actually looks more T-shaped, it is very noticeable that the polyxenes male does have longer and skinnier forewings. In both sexes, the zelicaon has a larger (wider) and hairier thorax.

Our black swallowtail (Papilio polyxenes asterius) female has starting laying eggs and we compared them to anise swallowtail (Papilio zelicaon) eggs. 

After not seeing any activity yesterday with our hand-paired black swallowtail (Papilio polyxenes asterius) female, we were a bit worried about how long she would take to start or if she would at all. This morning, which was sunny for once, we put her outside and still saw nothing for several hours. But after we went out for the afternoon and returned, we found several tips of the fennel plant (Foeniculum vulgare) clobbered in eggs. This egg laying style actually seems slightly more deliberate than zelicaon. 

The first thing that we thought when we saw the eggs was that there was something off about them, that they didn't look quite like zelicaon eggs. After taking an egg off and putting the eggs next to each other, we noticed that the polyxenes egg was much smaller, probably half the size, and more spherical. The zelicaon egg has a flatter base, making it look more dome-like. Another obvious difference is that the polyxenes egg is a darker yellow.