Why This Giant Moth Is Suddenly Everywhere in Metro Manila

The mysterious visitor is the tropical swallowtail moth (Lyssa zampa), a species native to Southeast Asia. With its striking pattern and wingspan reaching up to 16 centimeters, it's one of the largest moths in the region—and it's been turning up in the most unlikely places, from mall patios to school campuses to high-rise towers. 

A viral Facebook post by biodiversity researcher Edriel Lee suggests this sudden influx could be linked to something much bigger: climate stress.

When forests experience little to no rain, it often triggers trees to shed old leaves and grow new ones, which are easier for caterpillars to feed on. This abundance of food results in a rapid rise in the caterpillar population, but with it comes a problem, as the study notes.

With so many tropical swallowtail caterpillars feeding at once, they strip their host plants—particularly those in the Endospermum group—of all available leaves. Once the food runs out, the forest can no longer support the growing insect population. Lee explains that the adult moths are then forced to look for food elsewhere. Like many insects, they’re attracted to bright city lights, which is why they end up here in our concrete jungle. 

“Unfortunately, their host plants from the genus Endospermum—at least in Singapore—can only be found in forests and are absent in cities. As a result, the migrating moths are not able to reproduce,” Lee writes in his post.

In addition, he said that only the moths with strong flight capabilities—those with longer wings and lighter bodies—are able to make the journey into the city. This might seem like natural selection at work, but those traits aren't passed on since they can't exactly reproduce here. Meanwhile, those left in the forest become increasingly vulnerable to environmental changes. 

And because the tropical swallowtail moth is part of a larger food web, its disappearance could affect the entire ecosystem. 

“This is just one part of the bigger picture. We haven’t even touched on the possible impact of dry spells on the host plants themselves or on forest ecosystems as a whole,” Lee said.

The study might be based in Singapore, but the sudden wave of moths showing up in Metro Manila suggests the same could be happening here, too. As Lee says in his post, “The next time we see a tropical swallowtail moth, I hope it prompts us to reflect on what we can do to help protect Mother Earth.”    

Also read: You Found An Insect in Your Coffee—What Should You Do? An F&B Veteran Gives Advice