Assam researchers find invasive plants are key nectar sources for butterflies

GUWAHATI

Butterflies have revealed that some invasive plant species, disliked by conservationists and farmers, and avoided by herbivores, serve an ecological purpose.

Bishal Basumatary, a research scholar at Bodoland University, set out to document the butterflies and their nectar sources in Raimona National Park. The university is on the outskirts of Kokrajhar, the administrative headquarters of the Bodoland Territorial Region, about 220 km west of Guwahati.

The research was conducted under the supervision of Kushal Choudhury, an associate professor at the university’s Department of Zoology, between 2022 and 2025.

Their study documented 220 species of butterflies, 56 species of larval host plants, and 41 species of nectar plants in the 422 sq. km national park that forms a large transboundary conservation landscape with Bhutan’s Phibsoo Wildlife Sanctuary.

“One of the most significant findings is that Lantana camara, Chromolaena odorata, and Ziziphus mauritiana, which are generally regarded as invasive exotic species and are often excluded from forest management practices, serve as major nectar sources for a large number of butterfly species in the park,” Mr. Choudhury said.

Lantana camara and Chromolaena odorata are recognised among the world’s most aggressive invasive plant species and regarded as ecologically undesirable because of their negative impacts on native vegetation and ecosystem functioning.

Larval host plants serve as the food source for butterfly larvae during their developmental stages, whereas nectar plants provide nectar, the principal nutritional resource for adult butterflies. In natural ecosystems, the availability and diversity of larval host plants and nectar plants influence the richness and abundance of butterfly species as much as climate, habitat structure, seasonal variations, and other abiotic factors.

The study revealed that some invasive plant species provide abundant nectar supply for adult butterflies, particularly during periods when native wildflowers are scarce in the park. Their prolonged flowering period and high nectar availability were also found to have helped sustain butterfly populations during seasons of limited floral resources.

The researchers observed that Lantana camara attracted exceptionally large numbers of butterflies. “The species produces flower clusters that change colour as the flowers age, resulting in multi-coloured inflorescences that serve as highly conspicuous visual cues for foraging butterflies. Coupled with its continuous nectar production, this characteristic likely contributes to its high attractiveness and frequent visitation by diverse butterfly species,” they noted.

Suitable floral architecture

They also observed that the flowers of both Lantana camara and Chromolaena odorata are arranged in dense, rounded clusters composed of numerous tubular florets. “This floral architecture is highly suitable for butterfly feeding, providing easy access to abundant nectar and supporting frequent visitation by a wide range of species,” they said.

The study showed Lantana camara alone attracted more than 30 butterfly species between April and October, while Chromolaena odorata supported 24 butterfly species from December to February, demonstrating their complementary role in providing nectar resources across different seasons.

In addition to serving as nectar sources, several invasive plant species were also found to function as larval host plants, highlighting their multifaceted ecological importance. These include Ricinus communis, Senna alata, Portulaca oleracea, Sida rhombifolia, Cleome rutidosperma, Gomphocarpus physocarpus, Ageratum conyzoides, Chromolaena odorata, Tridax procumbens, Mikania micrantha, Mesosphaerum suaveolens, Spermacoce latifolia, Cyanthillium cinereum, Heliotropium indicum, Persicaria hydropiper, Persicaria sagittata, Sida acuta, Leucas aspera, and Urena lobata.

Many of these plants are considered weeds because they have little or no direct economic value. Consequently, they are frequently removed from natural landscapes.

“To the best of our knowledge, this is the first report from India highlighting the important ecological role of these invasive plants in supporting butterfly conservation. We believe these findings will be valuable for the Forest Department, conservationists, and nature enthusiasts,” Mr. Choudhury said.

The researchers suggested that the invasive species, given their butterfly-friendly role, could be considered in conservation planning. They recommended maintaining small, carefully managed patches of Lantana camara, Chromolaena odorata, and Ziziphus mauritiana in suitable areas of protected landscapes to provide a continuous nectar supply for butterflies, particularly during periods when native flowering plants are scarce.