Found Eggs and Larvae of Papilio glaucus on Tuliptree

We found eggs and larvae of the eastern tiger swallowtail (Papilio glaucus) on tuliptrees (Liriodendron tulipifera) located around the Cornell campus. These findings and their implications on oviposition habits of native glaucus and their flight patterns are discussed. 

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Today we found three first instar larvae, one fresh egg, and one partially developed egg of Papilio glaucus on tuliptrees (Liriodendron tulipifera) located around the Cornell campus. Two images of the first larvae are shown left and middle of the top row below, while the other two larvae have one image each. The fresh egg is shown middle and right of the second row and the partially developed egg is shown in the bottom row of images. 

All three larvae were found on the same very tall tuliptree tree growing in front of Teagle Hall, which was clearly landscaped. One of the larva was located on the lowest branch facing away from the building that is exposed to full sun. The other two were found on the opposite side of tree, albeit still exposed to a good deal of sun, also on relatively low branches. Although they are all first instar, they are not the same age in terms of development, which suggests that they could have originated from independant oviposition events, likely from different females.

The fresh egg was found on a tree, also very tall, at Cornell Botanic Garden. It was located to the side facing away from a building, again on a low branch. The partially developed egg was found on the outward facing side of a short and wide (presumably) wild-growing tree near the end of Beebe Lake that we can tell is exposed to full sun throughout the day. There are two other locations along the lake where tuliptree(s) grow but the trees there are taller and shaded by other plants and we were not able to find anything on them. 

There may be a general trend for eggs (and subsequent larvae) to be located on the lower branches of these large trees but our collections are biased because we are only able to search the lowest branches. Nonetheless, it does seem like these butterflies are not particularly high-flying and females will fly toward whatever they are most likely to encounter and is most convenient to lay on. Since their job is to seek suitable host plants through random investigation of plants, it would make sense that they would fly low while doing this since the vast majority of plants are not as tall as tuliptrees. 

The fact that larvae are all first instar and there are eggs is no coincidence. It is clear that this time marks the beginning of the flight for glaucus and that the flight might be relatively synchronized. Pupae likely began eclosing around the middle of May and according to the data obtained today, females begin ovipositing around the first week of June. We do not know whether pupae exhibit obligate diapause this far north of their range, but would not be surprising if they are naturally single brooded and univoltine at this locality. 

In comparison, tuliptrees leaves appear in the beginning of May and begin setting near the end of May. By June, leaves begin to mature and flowers bloom for several weeks. To illustrate, pictures of the tuliptrees we searched today are shown below. Tuliptree, of course, is not the only host plant of glaucus, which is widely acclaimed to be the most polyphagous swallowtail in the world, but studies indicate that it may be their most preferred host and that Magnoliaceae may be ancestral hosts. Host plant preference undoubtedly varies dramatically by region; far north, it would be assumed that they might highly prefer Prunus as well. In this collecting trip, we only searched tuliptree. 

What is a bit interesting is that the Teagle tree only had larvae and no eggs and that these larvae could have even come from different females. This indicates that, for some reason (perhaps or likely coincidence) butterflies in this "city" area consistently oviposited earlier than at either of the "natural" areas. In collecting wild eggs and larvae of other butterfly species, we have also noticed that certain locations tend to progress faster than others from year to year for when the plants grow and the time that they first receive eggs. 

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Brian Liang
Brian Liang is a student at Cornell University in Ithaca, New York pursuing an undergraduate degree in entomology. He is co-owner and a main contributor of the Liang Insects blog, insects articles, and site design.

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