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. . .

Rearing notes 7/23/17-7/25/17:

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. 

Rearing notes 7/18/17-7/19/17:

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:

Rearing notes for our hybrid Papilio glaucus × Papilio rutulus egg, laid by a captive P. glaucus female that was hand-paired with a wild caught P. rutulus male.

Rearing Notes 4/15/17-4/27/17:

See ​Papilio glaucus Female Finally Starts to Lay Eggs!

On the third day of attempting to get one of our Papilio glaucus females to lay eggs, she finally laid one!

Beginning on 4/13, after we set up a homemade little oviposition light box as described in this post, we have been hoping each day to get some of our hand-paired swallowtails to lay some eggs. 

After a quick feed of honey-water this morning at 9 AM, we decided to put the older of our two eastern tiger swallowtail (Papilio glaucus) females paired on 4/3 into the box with just a small sprig of plum (Prunus cerasifera) and switched on both lamps (our female pipevine swallowtail [Battus philenor hirsuta] escaped in the basement yesterday and still has yet to be recovered and the other glaucus has only just eclosed two days ago). Based on the activity of the previous two days with this female, there didn't seem to be much hope since she was already very worn and weak with brutally torn/crippled wings and a missing leg. We knew that if she really was going to lay eggs, it would take time and were not optimistic that she would be in the proper condition--or even alive for that matter--by the time she was ready. But when we checked on her about two hours later, we were quite taken aback that she had indeed finally laid a single egg right on the top of a fresh little leaf!

Being the first time that we have ever gotten any swallowtail outside of the machaon-group to actually oviposit in captivity, this has truly got to be one of the most exciting events in all our of years of rearing. What makes this even more exciting, or at least interesting, is that the female that laid the egg had been hand-paired with a wild caught western tiger (Papilio rutulus). We will admit that we aren't positive that the egg is actually fertile, but based on the behavior and abdomen girth of the female it at least seems that the pairing was successful. 

Given the unexpected success of this oviposition setup, we'll take this opportunity to analyze just what was different about this and the multitude of other occasions we have attempted to get Papilio glaucus to oviposit in captivity.  In the past, we have always taken the roomy approach in terms of the setup size, thinking that it was necessary that the female have enough room to fly in order to stimulate natural conditions and get her to lay. This time we used the smallest possible enclosure that could fit a sprig of host plant such that contact of the plant was essentially unavoidable unlike in the larger setup. Also different was that we used the heat lamps this time instead of natural sunlight. As you probably know, the weather here doesn't get very hot here so the lamps added a significant amount of heat that would be unachievable otherwise. However, we did realize this time that it probably was not necessarily the heat that got our female to start laying. Simply put, heat is not a direct stimulus for egg-laying; it seems only to hasten the process just as it hastens all other processes of these cold-blooded insects. Based on experience, very high heat is certainly not an absolute requirement for the swallowtails to lay so if our female was not planning on laying from the start she would not lay no matter how hot it is (the opposite is true in that if she is going to lay, she will do so even without higher than normal temperatures).

It is also important to note that our female is an old one, having eclosed on 4/4 (paired on 4/13). Tiger swallowtails are notorious for taking  very long time to develop their eggs. Obviously, the adult females begin with a handful upon emerging, but the higher the egg load, the more willing it seems that they are to lay. There is also some unconclusive research saying that females with higher egg loads are less picky when choosing host plants, which if true is something that we probably need to count on given the hosts that we used and have available to us. Our particular female very evidently had built up a generous supply of eggs based on how old she was and just by taking a look at the fullness of her abdomen. It is certainly much fuller than our younger female that eclosed on 4/3.  Insufficient egg load is one of the primary reason why it might take a long time before females begin laying in captivity. ​

Anyway, we are hoping that now that our female has gotten started, she will lay a some more in the coming days. Even a few eggs would be more than enough to please us if they all hatch and assuming they don't die for mysterious genetic reasons.