Papilio rutulus Eggs Hatch

Our western tiger swallowtail (Papilio rutulus) eggs, laid by a captive hand-paired female on July 7, have begun to hatch. 

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Finally, after nine days of anxious anticipation, the first western tiger swallowtail (Papilio rutuus) eggs have started to hatch. So far 16 of them have hatched, out of the original 45 (only 42 looked to have ever been fertile). Some of the remaining eggs look pretty close, but some are quite behind. It's a bit strange how they develop at such staggeringly different rates despite being laid at most only hours apart on the same day. Even with eggs on the same leaf, some have hatched and some have not. 

Anyway, we stuck the first six that hatched this morning onto willow (Salix), which will probably be our base host. By early afternoon, five more had hatched and we initially put them on our plum (Prunus) which we used as a host plant two years ago with two wild-caught larvae. Of all the host plant choices, willow and Prunus definitely seem to be the best for this species, especially in our region where it seems the ovipositing females have a strong preference for the two. Cherry would probably be superior to the plum, as it usually is with species that eat Prunus, but we don't have any of that. The problem with the plum is that we have a very limited supply of it (one tree) that doesn't seem to be doing very well. It has very little new growth (most of the leaves have been on the tree since March) and the leaves it does have are dry and covered in yellow speckles. We decided to be rash and still decided at first to try to use the plum as this is probably our only opportunity for a long time or forever, but after several hours and no feeding by the larva we gave in and put them and the five more newly hatched larvae onto the willow. Perhaps they would have started feeding on it later (quite likely, actually) but we didn't want to lose sight of the goal right now which is to get as many of them through as possible. We also suspected that the larvae would not take well to the plum since it took two months for the larvae two years ago to grow on it (during the same season, so leaf quality and temperatures were similar), which is abnormally long. ​

The newborn larvae were surprisingly difficult to handle despite their relatively large size to other swallowtails (about 3 mm). Like anise (Papilio zelicaon), they make silken mats immediately after they finish eating their egg shell, making it hard to pull them off onto the new leaves. At this time, they thrash around violently and, although they don't stick out their horns (which are dark red at this stage) too much like the anise newborns, they sometimes regurgitate which is even worse. But once we can get them to settle down, hopefully this will actually be a very easy species to rear in bulk.

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Authors
Brian Liang

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