Brihat Samhita
प्रविशति यदि खद्योतो जलदसमीपेषु रजनीषु । केदारपूरं अधिकं वर्षति देवस्तदा न चिरात् ॥ २८-२३ ॥
If fireflies enter and gather near the clouds during the nights, then the god (of rain) soon pours down rain in abundance, filling the fields and reservoirs.
english translation
pravizati yadi khadyoto jaladasamIpeSu rajanISu । kedArapUraM adhikaM varSati devastadA na cirAt ॥ 28-23 ॥
hk transliteration by Sanscript