Collecting Heaps of Cresphontes Eggs

Today we found a whopping three dozen giant swallowtail (Papilio cresphontes) eggs scattered among several rue (Ruta graveolens) plants at the Cornell Botanic Gardens. 

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It has been two days since we last visited the Cornell Botanic Gardens. We spent the weekend exploring other locations, thinking that we might have better luck finding new things since we have already been to the gardens many times since coming to Ithaca. When we came back for a brief checkup late this afternoon, we didn't really have high hopes for finding much, especially because it was not sunny and it had not been sunny in the previous days either. 

We were thoroughly surprised when we found several rue (Ruta graveolens) plants that were clobbered in Papilio cresphontes eggs. Almost all of them look to fresh, and because we check the plants carefully every time we have ever been to the garden, it was quite apparent that some female(s) for some reason just decided to let herself go and spilled everything. This pattern of abrupt egg laying, while probably holds true to some extent in many swallowtails and other species, is actually quite interesting based on our experience with female cresphontes. The things don't emerge with a single matured egg in them (after that it seem to take ages to build the eggs up) and when skinny wild-caught females are put to work, they never lay or show any behavior indicating a desire to lay. In the wild, the females probably nectar for many days before they finally decide to fulfill their duty, which can explain what we saw. It just so happens that there weren't that many rue plants and the plants themselves are very small (relative to tree hosts), both of which are ideal conditions to seal the deal for finding eggs in large numbers. Keep in mind that although we alone have seen or captured several females over multiple days in this area and the cresphontes flight is at a peak at this time of year in New York, this is our first time in ten days of looking that we have seen something like this. 

The eggs were consistently laid at the periphery of the plant, much like P. zelicaon and parsley (Petroselinum) (which has very similarly shaped leaves as rue). Also, most of the eggs seem to be laid on the bottom half of the plant, in what can be considered more hidden locations. Every single one was laid on the upper side of the leaf, which is typical of swallowtails. Like Battus philenor eggs, the grainy substance on the cresphontes eggs doesn't seem to give them a very good stick (at least on rue leaves) because a lot of the eggs fell off as or after they were collected. 

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Authors
​Brian Liang

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