Urban Areas as Potential Sinks for Tropical Swallowtail Moth Lyssa zampa

Abstract

(1) The tropical swallowtail moth Lyssa zampa received much public attention during its years of mass emergence in Singapore and Southeast Asia. However, despite its prominence, little is known about its population demographics and spatial ecology. This study aims to establish the annual abundance of L. zampa, determine its spatial patterns of occurrence, and examine morphological variation demonstrated by L. zampa with an emphasis on comparing urban vs. forest areas in Singapore. (2) Various sources (field surveys across 18 sites, citizen science datasets and expert knowledge) were used to catalogue L. zampa records from 2011 to 2020 and analyse its seasonal abundance. (3) We confirmed the seasonal peak of L. zampa emergence to be between May and July, with an unusually high mass emergence in 2014. The intensity of emergence was associated with the intensity of a dry spell in February of that year. The total number of L. zampa sighted in urban areas was higher despite the moth’s host plant being a tree that is restricted to mature forests and is absent from urban areas. This suggests that the occurrence of L. zampa in urban areas is likely due to the moth’s attraction to bright city lights. Our morphometric measurements further show that L. zampa individuals in urban areas have greater wing length and lighter body weights (smaller body widths) than their forest counterparts. (4) This implies that urban areas are not only drawing moths that are unable to find the host plants and, therefore, cannot produce offspring but are also attracting larger and better flyers out of forest areas. This situation is only likely to worsen as climate change intensifies and dry spells become longer and more intense.