Late Season Anise Swallowtail Chrysalis Harvest

Today we finally harvested the handful of chrysalises from our very late brood of anise swallowtail caterpillars (Papilio zelicaon).

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Ever since the weather started going downhill at the start of this month, our October brood of anise swallowtails (Papilio zelicaon) have been experiencing some seriously slow growth rate (they are being reared outdoors). Daily temperatures are around 60 degrees Fahrenheit now and it rains often. 

When we first released the three dozen or so fourth instar caterpillars onto our sweet fennel (Foeniculum vulgare), they were extremely close, probably only a day or two apart in development at the most. After all, they are all siblings that hatched from eggs laid on the same day. But at this point, the faster growing ones in the fifth instar have long pupated while the slower ones have lagged behind dramatically. As of today we still have two very young fifth instar caterpillars outside, a few that are prepupae, and the rest already chrysalises. 

Because of the late season environment, we noted a few weeks ago about the particularly dark forms of these caterpillars. We even took a few pictures of then fifth instars which had very thick black bands. Well, it turns out that some of the more recent fifth instars such as the two young ones we still have right now are even darker.  

But what is even more interesting is that some of the chrysalises formed by these late season caterpillars are also extremely dark in color, more so than what we normally saw in the summer. We collected seventeen chrysalises today on our screen cage that were formed by these caterpillars and almost all of them were very dark brown/black forms and not just a tan. Of these seventeen, two were especially black, the blackest anise chrysalises we have ever seen. They are shown below:

The pupation site substrate has well documented as being an influential factor on the color of the pupae in certain swallowtails, including machaon-group species (of which zelicaon is a member of), but we have never read anything about what can effect the overall intensity of the color. In our experience, putting a prepupal caterpillar on a dark green substrate versus a lighter green substrate usually both produce green forms but very clearly does not seem to produce any noticeable effect on the shade of the green; the same holds true in the case of a pitch black substrate versus a brown substrate. That leaves us to conclude that what is more likely the case with our chrysalises probably has something to do with seasonal factors like temperature and photoperiod, the same phenomenon we saw which produced the dark form caterpillars that formed these chrysalises. 

- Brian