Light pollution at night impacts monarch butterfly growth and performance

Exposure to artificial light at night (ALAN) increased caterpillar growth rates by nearly 16%.

• ALAN consistently shortened larval development time, leading to an 8% increase in adult fresh mass across two milkweed species.
• Host plant species interacted with ALAN to affect wing morphology, with butterflies on one species showing 7% larger wings under ALAN.
• The migratory generation of monarchs developed slower and emerged with 44% less body mass compared to earlier breeding generations.
• ALAN's enhancement of larval growth was comparable to the effects of feeding on a preferred milkweed species.
• Light pollution at night alters the developmental trajectory of monarch butterflies, impacting their life histories.

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