Observation of developmental stages of swallowtail butterfly in Kathmandu, Nepal

My observation notes on the developmental stages of Papilio polytes (swallowtail butterfly) in Kathmandu, Nepal

By Bidhan Adhikary

The ongoing global pandemic had kept me confined at home all year. It was a time of reflection and picking up old and new hobbies. I also helped around in our rooftop garden, where we have some ornamental plants and a small miniature vegetable garden. And during the fall of 2020, I had the opportunity to observe the developmental stages of swallowtail butterflies.

It was around mid-September when I first noticed what looked like a lot of bird droppings in my citrus plants (Figure 1 and 2). Upon closer inspection, it turned out to be caterpillars of the Papilio polytes, a swallowtail butterfly (which I later identified).

Figure 2. The early larva share resemblance to bird droppings.

When I first noticed the caterpillars, most of them were in different stages of their developmental cycle. I was a bit disappointed as I felt I missed the eggs and the hatching stages. But over the next few weeks, I was able to photograph the eggs and the early stages too.

The caterpillars kept on feeding and molting, all the while destroying our citrus plants until they reached their final instar stage. Seeing my curiosity, my mom left these caterpillars in peace to munch away our precious plants. They had become pests at this point as they covered and stripped bare all the green leaves of our few citrus plants (Figure 3 and 4).

Figure 3. Citrus plant in early stage of infestation.

Figure 4. Citrus plant in late stage of infestation.

The fascinating thing about this species is that every stage of their developmental cycle looks strange. First, it looks like bird poop. The more mature larval stages look like miniature snakes! They have eye-like spots on their body and a defensive organ known as osmeterium, which resembles a fleshy forked (Y-shaped) snake tongue. Osmeterium is situated just behind their head (Figure 5), in the prothoracic segment, and usually stays hidden. When a threat is detected, the osmeterium pops out. Combined with the eyespots, the larva resembles a snake, startling predators like birds and lizards. Osmeterium can also emit a foul odor to deter some predators. That’s already two different forms of defensive mimicry just in the larval stage.

Figure 5. The larva displays the fleshy forked (Y-shaped) osmeterium after detecting a threat. Osmeterium in full display (left) and while withdrawing (right).

Then one day, I noticed a green chrysalis in the corner of a wall (Figure 6). It was a smooth, crescent structure hanging by fine silky threads, and it looked like one of those creatures from a science fiction movie. But then again, these fictional creature designs draw a lot of inspiration from bugs, insects, and all forms of biodiversity.

Figure 6. Chrysalis formed on wall that was later brought in for observation.

Figure 7. The chrysalis changes into a transparent color indicating that the butterfly is almost ready to emerge.

As you can imagine by now, I was very much invested in this and curious to find out which butterfly would emerge. So the first few days, I kept returning to check. Then I realized I could relocate it in my room and observe it. I had read that the day before emerging, the butterfly chrysalis would become more transparent (Figure 7). The adult butterfly emerged from the chrysalis after 12 days and I managed to take some good photos of the process (Figure 8).

Figure 8. Newly emerged butterfly wings are wet and wrinkled.

Figure 9. The male butterfly which emerged from the chrysalis under observation.

It turned out to be a male Papilio polytes (Figure 9), also known as the common Mormon, a species of swallowtail butterfly widely distributed across Asia. I released it back in my garden. The females of this species exhibit Batesian mimicry, in which an edible species of butterfly will look similar to an unpalatable butterfly species to deter predators from eating it. I could not document the female butterfly of this species, but I do have an old photo of a courting pair of male and female swallowtail butterflies which I have included below (Figure 10).

Figure 10. Courting pair of male (left) and female (right) swallowtail butterflies.

Later I saw a live formation of another chrysalis on a branch of my citrus plant, and it too emerged after 12 days. And then there was one chrysalis (formed on a piece of bamboo), which instead of turning green, changed into a woody brown color (Figure 11 and 12). It stayed dormant over winter from mid-December to the first week of March for a total of 83 days, after which it finally emerged (Figure 13).

Figure 11. Formation of a new chrysalis.

Figure 12. An woody brown overwinter chrysalis.

Figure 13. The empty shell after emergence of adult butterfly.

And with that, my home project came to a satisfactory conclusion. I have compiled the images to illustrate the different developmental stages of this beautiful butterfly (Figure 14). And my citrus plants are doing just fine. Now that spring has arrived, they are full of fresh new leaves.

Figure 14. Developmental stages of Papilio polytes from egg to an adult butterfly.

If you are interested to learn more about Papilio polytes, the common Mormon swallowtail butterfly, you can find additional information on the following links:

Bidhan Adhikary is a wildlife researcher from Nepal. He is interested in wildlife behavior, habitat ecology, and conservation education. LinkedIn|Blog [Email: bidhan@ekadesh.com]