Getting Eggs out of Papilio polyxenes asterius & Egg Comparison with zelicaon

Our black swallowtail (Papilio polyxenes asterius) female has starting laying eggs and we compared them to anise swallowtail (Papilio zelicaon) eggs. 

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After not seeing any activity yesterday with our hand-paired black swallowtail (Papilio polyxenes asterius) female, we were a bit worried about how long she would take to start or if she would at all. This morning, which was sunny for once, we put her outside and still saw nothing for several hours. But after we went out for the afternoon and returned, we found several tips of the fennel plant (Foeniculum vulgare) clobbered in eggs. This egg laying style actually seems slightly more deliberate than zelicaon. 

The first thing that we thought when we saw the eggs was that there was something off about them, that they didn't look quite like zelicaon eggs. After taking an egg off and putting the eggs next to each other, we noticed that the polyxenes egg was much smaller, probably half the size, and more spherical. The zelicaon egg has a flatter base, making it look more dome-like. Another obvious difference is that the polyxenes egg is a darker yellow. 

We have actually noted the same size and color difference with Papilio rutulus and glaucus eggs. Rutulus eggs are humongous and flatter and are yellow-green when first laid instead of dark green as in glaucus. The size difference might explain the drastic difference in female abdomen size, at least in zelicaon and polyxenes which we have compared side by side. We have yet to find out if there are also significant differences in the size and weight of the larvae or pupae between the two species. Certainly, the newborn larvae would be different in size. Larger size of the first instar generally seems to be an adaptation for eating tough host plants, but we don't really know what our zelicaon or the polyxenes we have historically fed on that may have created the appropriate selective pressures. 

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Authors
Brian Liang

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