Collecting Papilio troilus Eggs

Today we went collecting spicebush swallowtail (Papilio troilus) eggs for the first time at Mundy Wildflower Garden in Ithaca, New York.

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In the past week, we have been focusing solely on locating the larval stage of the spicebush swallowtail (Papilio troilus) on the spicebush (Lindera benzoin) at Mundy Wildflower Garden. The big problem with this species is that it is difficult to focus on finding the larvae and the eggs at the same time because the larvae and their conspicuous leaf nests are always on the uppersides of leaves whereas the eggs are always laid on the undersides.

Yesterday we realized that we had inadvertently brought home an egg on the cutting we picked the day before, making our first ever egg of the species after finding 18 larvae. It was already murky with black spots at the top (the larva's head) when we first saw it, and at some point it must have turned completely black because it already hatched today. The newborn larvae are a pale gray with white, which explains the light coloration of the egg that actually has a clear shell. Except for the difference in color and the small size, they look almost identical to P. rutulus newborn larvae, a fellow member of Pterorous​. 

Anyway, today we set out to search for eggs exclusively at Mundy where we have already depleted most of the larvae anyhow. We ended up finding a total of 15 eggs, but they did not come easy. . . I think we learned quite a lot from this trip about the butterflies' preferences. Almost all of the eggs were found on two trees located on the perimeter of the garden and near water. Because spicebush is such a small tree, it is normally shaded in the garden itself where there are a lot of other trees; the shade gets progressively worse as you go through the trails. Although we have found larvae on many of the trees inside the garden and some, to our great surprise, on completely shaded and well hidden trees deep within the trail, it seems that in the end, the open areas are still the best as one would expect. We wasted an obscene amount of time searching the shaded plants which, perhaps also partially by bad luck, did not have any eggs whatsoever. Most of the eggs that were not on the two sunny trees were on a very small tree near the perimeter. We also found four first instar larvae on it hiding out on the underside of the leaves; it seems that because the eggs are laid on the underside, the newborn larvae stay there and don't make nests until the second instar.

On the trees themselves, the eggs were only ever located near the tips of branches, particularly ones that just out from the rest of the plant, and somewhere off to the side of the mid-vein in the center of the leaf. This preference for the periphery or isolated portions of the plant is shared by P. zelicaon and is probably something that is true of most swallowtails in general. There did not ever seem to be a single branch with more than one egg. Although swallowtails usually prefer new growth, especially in hosts with tough leaves such as Rutaceae, we did not observe this in today's collection. It is to be noted, however, that little to no growth exists on the trees during this time of year.  

The newly laid eggs are a pale, white, and somewhat translucent. The slightly olders ones seem to be slightly yellower and alost resemble newly laid eggs of P. zelicaon. Development is otherwise not very obvious in the species. 

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Authors
​Brian Liang

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