Butterfly populations in the United Kingdom may face significant declines next year due to the effects of this summer’s drought on caterpillar survival, experts have warned. Following a year marked by high butterfly numbers, researchers caution that the adverse conditions experienced during the caterpillar stage could result in population crashes similar to those observed after severe droughts in 1976 and 1995.
Recent butterfly counts have shown an encouraging increase in adult sightings, with the Big Butterfly Count registering the second-highest tally in its history in 2026. However, scientists emphasize that the success of adult butterflies in warm, sunny weather does not necessarily translate into robust future populations. Prof Richard Fox of Butterfly Conservation highlighted the vulnerability of caterpillars and their host plants to extreme weather events, noting that while adults benefit from sunny conditions for flying, feeding, and breeding, these same conditions can negatively impact the plants caterpillars rely on for nourishment and shelter.
“The very same weather that made it a good year for butterflies could mean we’re on course for a population crash, which could take years to recover from,” Fox said, referencing past droughts that led to severe damage in butterfly numbers the following year. One species particularly affected by this year’s drought is the green-veined white, which has experienced a 54% decline in sightings compared to previous years, underscoring the sensitivity of certain butterflies to prolonged dry conditions.
While current adult butterfly numbers may appear promising, the ecological consequences of drought on early life stages suggest prolonged challenges ahead for butterfly conservation efforts. The interplay between extreme weather and insect life cycles remains a key area of concern for scientists monitoring biodiversity in the face of climate variability.