Tropical swallowtail moth: Why is this insect all over Metro Manila—and social media?
A dark-colored insect reportedly spotted across Metro Manila has captivated social media users, prompting widespread curiosity about what this phenomenon could be.
In a now-viral Facebook post on June 19, Edriel Lee, a biology graduate from the University of the Philippines Diliman, shared a photo of the tropical swallowtail moth (Lyssa zampa). In his post, Lee noted that he would usually take some snapshots of the moth and then go about his day.
"But as I began to see more and more of them, both in person and in social media posts, it made me wonder, why?" he said.
Commenters eagerly replied with photos of the tropical swallowtail moths they'd encountered. These insects were pictured everywhere, from a glass door in Bonifacio Global City to a Makati Central Business District sidewalk and even outside someone's home in Fairview.
Physical traits
Based on Lee's photo, the tropical swallowtail moth has broad and triangular deep-brown wings, with the hindwings ending in long, narrow tails resembling those of a swallow (hence the insect's name). The wings also have an off-white stripe that looks like a "V."
The body, meanwhile, appears to be covered in fine, short hairs.
Jade Badon, an assistant professor at the UP Los Baños Institute of Biology, told PhilSTAR L!fe that the tropical swallowtail moth belongs to the moth family Uraniidae, which includes day-flying moths. (Moths are generally nocturnal.)
"It is different from other moths based on the morphological characters such as their wing venations," Badon said.
UP Wild, a flora and fauna community of UP Diliman, in a 2024 post, also noted that the moth's wings can reach a maximum wingspan of six inches, or as long as one's hand.
It noted that aside from the Philippines, it can also be found in other parts of Southeast Asia, such as Indonesia and Malaysia.
'Still understudied'
Badon noted that the tropical swallowtail moth can be seen in forested habitats and is also commonly spotted near lights in houses or any other sources of light.
According to him, 2025 has the most sightings of a tropical swallowtail moth compared to previous years or in other months, being mostly abundant between May and June.
"In our PhiLep (Philippine Lepidoptera) database, we do have records but irregular recordings or sightings," he said.
Still, Badon noted that the moth's behavior, biology, and ecology remain understudied.
Several possible factors as to why the moth is being seen in the city may have something to do with the climate. Badon noted that the species started coming out in the Philippines when the first rains arrived in the country.
"With rain, it is expected that flowers may bloom and the moth's host plants may develop fresh shoots for females to lay their eggs and caterpillars to feed," he said, adding that the rains give cooler temperatures that may be more favorable for the insect.
Badon suggested the tropical swallowtail moth could indicate the start of the rainy season, which PAGASA declared began on June 2 and is expected to last until November. He added that this is "just like other butterflies that will start flying or emerging at the start of the rainy season in the country."
Aside from that, Badon attributed the recent phenomenon to moths being attracted to light.
"They may have confused the city lights with daylight, so they fly toward areas with lights," he said. "They fly toward it, hoping to find nectar sources to feed on or to look for any potential mate."
While the moth has trended on social media recently, he noted that it's also likely that people just started noticing it.
Emergence in Singapore
Because of his curiosity toward the tropical swallowtail moth, Lee said he ended up accessing a 2023 article from the open-access platform MDPI (Multidisciplinary Digital Publishing Institute) titled, "Urban Areas as Potential Sinks for Tropical Swallowtail Moth Lyssa zampa" by Singaporean researchers Anuj Jain, Lin Yu Ng, and N. Sivasothi.
Their study aimed to find the reason for the tropical swallowtail moth's "unusually high mass emergence" in Singapore between May and July 2014.
They found that the intensity of the insect's emergence was associated with the intensity of a dry spell in February of that year.
"Dry spells can trigger population booms in insects. They may cause mass flowering, leaf renewal, and lowered plant defenses. Hence, an increase in population can be expected, benefiting the herbivorous Lyssa zampa caterpillars," Lee said.
But host plants are at risk of declining as more larvae feed on them, forcing moths to migrate to look for other places to find food.
As moths go to the cities due to the bright lights, little did they know that their host plants can only be found in forests and are absent in cities, such as the case in Singapore.
The bigger picture
Lee said the migrating moths aren't able to reproduce due to the lack of host plants in the city. He warned about the problems for the genetic health of the tropical swallowtail moth being in the city, such as the inability to pass traits like light bodies and long wings to the next generation.
When those that remain don't have as much flight prowess, Lee noted that future generations of the tropical swallowtail moth are at risk of developing shorter wings, compromising their fitness.
"Over time, this could contribute to local declines or reduced resilience, especially if new environmental pressures arise," he said. "And as part of a greater food web, their loss could have a tremendous cascading effect."
Lee noted that aside from the moth's situation, dry spells also have an impact on the host plants themselves or on forest ecosystems as a whole.
"Unfortunately, dry spells are becoming more frequent and prolonged due to global warming," he said. "The appearance of these moths could be another sign of that, and we may begin to see more phenomena like this over time."
"So the next time we see a tropical swallowtail moth," Lee added, "I hope it prompts us to reflect on what we can do to help protect Mother Earth."
