Wasp Populations Decline in UK Amidst Extreme Summer Weather

Wasp populations in the United Kingdom appear to be declining this summer. Scientists suspect extreme weather, including temperature fluctuations and heatwaves, may be responsible. Researchers note a significant reduction in wasp sightings and pest control requests. The Big Wasp Survey, a national monitoring program, will provide definitive data later this year. However, current observations suggest a concerning trend.

Wasps are vital to ecosystems. They act as pest controllers, pollinators, and decomposers. The spring of 2026 began with warm, dry conditions, which typically benefit wasp nest establishment. However, this period was marked by unprecedented heat, followed by cold, damp days and chilly nights. These extreme weather shifts may have caused queen wasps to abandon or die in their nests, reducing initial populations.

Subsequent heatwaves across the UK further impacted insect populations. While some insects, like butterflies, may thrive in warmer conditions, all insects have a critical thermal maximum (CTmax). Exceeding this temperature can lead to desiccation, muscle spasms, and stupor. For honeybees, the CTmax is around 49 degrees Celsius (120 degrees Fahrenheit), but ground surfaces in the UK exceeded 50 degrees Celsius (122 degrees Fahrenheit) during heatwaves. Wasp CTmax is estimated to be around 45 degrees Celsius (113 degrees Fahrenheit).

Observations also indicate that the few wasps seen this summer are unusually small. Insect adult size is determined by the food quality and quantity received during larval development. Typically, later-season worker wasps are larger due to increased colony foraging capacity. The current small size suggests limited prey availability or direct effects of heat. Larvae reared at higher temperatures often develop faster but reach a smaller pupation size. This trend aligns with a century-long observation of social wasps shrinking due to global warming.

Researchers are asking the public to report wasp sightings and observations. This data will help scientists better understand the impact of environmental changes on these insects. The Wasp Picnic Survey 2026 encourages participants to submit photos of wasps eating either ham or jam.