Citizen Science Reveals Lepidopteran-Visitor Flower Network in Metro Manila, Philippines: A Preliminary Study

This preliminary study leverages a decade of iNaturalist observations to map a generalized Lepidopteran-flower network in Metro Manila, revealing that exotic and ruderal plants serve as crucial hubs for sustaining endemic butterflies and demonstrating the value of citizen science for informing urban pollinator conservation.

The Gist

Imagine Metro Manila not just as a concrete jungle of traffic and skyscrapers, but as a giant, bustling marketplace. In this market, there are two main groups of characters: the butterflies and moths (the shoppers) and the flowers (the stalls selling nectar).

For a long time, scientists thought that in such a busy, crowded city, the only "shoppers" were the common ones, and the "stalls" were just random weeds. But this new study, led by Samuel Brillo and Rodelina Deyto, decided to take a closer look using a very clever tool: iNaturalist.

Think of iNaturalist as a giant, global photo album where regular people (citizen scientists) upload pictures of nature. Instead of hiring a team of biologists to spend years chasing butterflies in the heat, the researchers simply asked: "Hey, everyone who has a camera, show us your photos of butterflies landing on flowers in Manila!"

Here is the story of what they found, broken down simply:

1. The "Marketplace" Map

The researchers took 126 verified photos from 2015 to 2025 and turned them into a network map. Imagine a spiderweb where one side is the butterflies and the other is the flowers. If a butterfly is seen on a flower, a string connects them.

• The Result: The web is "generalized." This means most butterflies aren't picky eaters. They don't just visit one specific flower; they hop from one to another.
• The Super-Stars (Hubs): Just like a busy mall has a few popular food courts, this city has a few "super-stalls." The flowers Tridax procumbens (a common weed), Lantana, and Ixora (a popular garden shrub) were the most visited. They were the "food courts" where almost every type of butterfly stopped by.
• The Popular Shoppers: The butterflies Papilio demoleus (Lime Swallowtail) and Leptosia nina (Psyche) were the most frequent shoppers, visiting almost everything.

2. The Color Code

If you walked into this flower market, what colors would you see the butterflies flocking to?

• White, Yellow, and Pink: These were the "bright neon signs" that attracted the most attention.
• The Analogy: Think of white and yellow flowers like bright yellow taxis in Manila. They are easy to spot from far away, so the butterflies (who are like drivers looking for a fare) naturally gravitate toward them.
• The Moths: The night-flying moths (like the Amata heubneri) mostly stuck to white flowers. This makes sense because white is the most visible color in the dark, like a white shirt in a dimly lit room.

3. The VIPs (Endemic Species)

The most exciting part of the story involves the "VIPs"—the butterflies that are native only to the Philippines and found nowhere else on Earth.

• The Characters: The Philippine Wanderer (Pareronia boebera), the Golden Birdwing (Troides rhadamantus—a huge, beautiful butterfly), and the Philippine Five-Ring (Ypthima stellera).
• The Discovery: Scientists thought these rare butterflies might be struggling in the city. But the photos showed they were actually hanging out in gardens and parks, sipping nectar from common plants like Ixora and Mussaenda.
• The Lesson: Even though these plants are often just "ornamentals" (pretty decorations) or "weeds," they are actually life-support systems for these rare, local celebrities. The city's gardens are keeping them alive!

4. The Catch (The "Filter" on the Photos)

The authors are very honest about the limitations of their method.

• The Bias: Because they relied on photos, they saw what people wanted to photograph. People love taking pictures of bright, colorful butterflies and obvious flowers. They rarely photograph a dull brown moth on a dirty weed in a dark alley.
• The Analogy: It's like trying to understand a city's food culture only by looking at Instagram posts. You'll see a lot of fancy burgers and colorful smoothies, but you might miss the delicious, humble street food that nobody posts about.
• The Reality: The study likely overestimates how much butterflies love white and yellow flowers, simply because those are the ones easiest to spot and photograph.

The Big Takeaway

This study is like a first draft of a city guide for butterflies.

It tells us that Metro Manila is actually a surprisingly good home for butterflies, provided there are flowers. Even in a concrete jungle, if you plant a few Ixora bushes or let some Tridax weeds grow by the roadside, you are creating a "nectar highway" that helps both common butterflies and rare, endemic species survive.

In short: You don't need a massive, untouched forest to save butterflies. You just need a few colorful flowers in your garden, and the city's "shoppers" will find their way there. Citizen science helped us realize that the city is already doing some of the heavy lifting for nature; we just need to keep the "stalls" open.

Technical Summary

1. Problem Statement

Urbanization in tropical megacities like Metro Manila leads to habitat fragmentation, loss of native flora, and disruption of ecological interactions. While pollination is critical for biodiversity, Lepidopteran-mediated pollination (butterflies and moths) remains poorly documented in urban environments compared to bee pollination. Traditional field-based studies are often logistically difficult, time-consuming, and costly in dense urban settings. There is a significant knowledge gap regarding:

• Which Lepidopteran species visit flowers in Metro Manila.
• The structure of the plant-pollinator interaction network in this urban matrix.
• The specific floral resources (native vs. exotic) sustaining endemic and generalist Lepidoptera.

2. Methodology

The study employed a citizen science-based research design utilizing opportunistic data from the iNaturalist platform.

• Data Source: Research-grade (RG) observations from the "Lepidoptera of Metro Manila" community project, collected between September 2015 and November 2025.
• Inclusion Criteria:
  1. Direct visual contact or landing of a Lepidopteran on a flower.
  2. Visible reproductive structures or positions suggesting pollination.
  3. Geolocation within Metro Manila political boundaries.
• Data Processing:
  • Filtering: 126 validated records were extracted from an initial pool of 1,339 RG observations.
  • Verification: Taxonomic names were standardized using Plants of the World Online (POWO) and Co's Digital Flora of the Philippines. Ambiguous species were annotated with "cf." (confer).
  • Metadata Extraction: Observer details, location, time of day, visitor species, plant species, and flower color were recorded.
• Analysis:
  • Bipartite Network Analysis: Constructed to visualize interactions between Lepidopteran visitors (one set of nodes) and flowering plants (the other set) to determine network structure and identify hubs.
  • Heatmap Analysis: Generated to map associations between visitor species and flower colors.
  • Tools: Data analysis and visualization were performed using Python.

3. Key Contributions

• First Urban Network: This is the first study to construct a Lepidopteran-visitor flower network specifically for Metro Manila.
• New Nectar Associations: The study documents previously unreported nectar sources for three Philippine endemic butterfly species:
  • Pareronia boebera (Philippine Wanderer)
  • Troides rhadamantus (Golden Birdwing)
  • Ypthima stellera (Philippine Five-ring)
• Methodological Validation: It demonstrates the efficacy of using opportunistic, research-grade citizen science data to generate baseline ecological insights in data-deficient tropical cities, despite inherent sampling biases.

4. Key Results

A. Taxonomic Composition

• Visitors: 38 Lepidopteran taxa identified (34 butterflies, 4 moths).
  • Dominant families: Pieridae (38 obs), Papilionidae (30 obs), and Nymphalidae (31 obs).
  • Endemic species recorded: Pareronia boebera, Troides rhadamantus, and Ypthima stellera.
• Plants: 49 flowering plant taxa identified.
  • Dominant families: Asteraceae (32 records) and Rubiaceae (20 records).
  • Origin: The network is heavily dominated by exotic species (97 records), particularly weedy exotics (Tridax procumbens, Lantana camara) and ornamentals (Ixora spp., Catharanthus roseus). Native plants accounted for only 25 records.

B. Network Structure

• Generalized Interaction: The network exhibits a generalized structure rather than a specialized one.
• Hubs:
  • Key Butterfly Hubs: Papilio demoleus, Leptosia nina, Ypthima stellera, Hypolimnas bolina, and Eurema hecabe.
  • Key Plant Hubs: Tridax procumbens, Lantana camara, Ixora spp., Alternanthera sessilis, and Catharanthus roseus.
• Long Tail: A significant portion of the network consists of rare, low-frequency interactions (single or double observations), indicating the presence of specialized or rare interactions that are difficult to capture systematically.

C. Floral Preferences

• Color Bias: Strong preference for white, yellow, and pink flowers.
  • White: Highest interaction frequency (e.g., Tridax procumbens, Ixora).
  • Yellow: Dominated by Pieridae (e.g., Eurema hecabe, Catopsilia pomona).
  • Moths: Predominantly associated with white/pale flowers, consistent with crepuscular/nocturnal foraging.
• Spatial/Temporal Distribution: Observations were heavily concentrated in Quezon City (67 records), particularly in university campuses and parks. Most data (75%) was collected during the wet season (June–November).

5. Significance and Implications

• Ecological Resilience: The study reveals that urban environments, despite being dominated by exotic and weedy flora, can sustain diverse Lepidopteran assemblages, including endemic species. Cultivated ornamentals and ruderal plants act as critical "stepping stones" for pollinator survival.
• Conservation Strategy: The findings suggest that urban planning should prioritize the maintenance of nectar-rich gardens and roadside vegetation featuring high-visibility flowers (white/yellow/pink) to support both generalist and endemic butterflies.
• Citizen Science Utility: The study validates iNaturalist as a cost-effective tool for uncovering undocumented ecological interactions. While subject to observer bias (favoring conspicuous species and accessible locations), it provides a necessary baseline for hypothesis generation and future targeted field validation.
• Future Directions: The authors recommend integrating citizen science data with systematic field surveys to quantify interaction strength and correct for spatial/temporal biases, ultimately guiding biodiversity-friendly urban planning in the Philippines and similar tropical megacities.