Britain is experiencing a notable decline in wasp populations this year, a trend researchers believe is linked to extreme and fluctuating weather patterns. Professor Seirian Sumner, a behavioural ecologist at University College London, points to multiple indicators suggesting the insect’s diminished numbers, including reduced calls to pest-control services and a drop in media reports about wasp activity.

According to Sumner, pest-control workers have reported an unusually quiet season, with fewer nests found in homes and gardens compared to previous years. Similarly, the media attention that typically accompanies wasp infestations has been largely absent, contrasting sharply with last year’s widespread complaints when she frequently provided interviews on the subject.

Experts attribute the decline to what Sumner describes as a “triple whammy” of adverse weather conditions. While the spring initially showed promise for wasp populations, it was disrupted by spells of cold, wet weather and near-frost conditions in May that may have harmed queen wasps or destroyed early nests. Following these setbacks, heatwaves caused drought-like conditions that affected food availability by reducing nectar sources and the abundance of insects that adult wasps hunt to feed their larvae. Observations indicate that the wasps present have often appeared smaller than usual, suggesting nutritional stress.

Although fewer wasps might be seen as a relief during outdoor activities such as picnics and visits to beer gardens, Sumner warns that the decrease could have broader ecological consequences. Wasps play a role as natural pest controllers by preying on flies, crop-damaging insects, and other pest species. Their absence may be contributing to a rise in fly populations, as noted by Sumner’s own increased encounters with flies at home. This shift could potentially lead to greater reliance on chemical pesticides, raising concerns about agricultural and environmental impacts.

To better understand and monitor wasp populations, Sumner has initiated a citizen science project called the Ham or Jam survey. Participants are encouraged to observe wasps visiting outdoor meals and note whether the insects are attracted to protein sources such as ham or chicken sandwiches, which wasps collect to feed their larvae, or to sugary foods like jam, which they consume for themselves. Observers can report their findings through a simple online form.

In addition, Sumner suggests that offering a small piece of food left at the edge of a plate—referred to as a “wasp offering”—may assist the insects during this challenging period while providing valuable data to researchers.

This ongoing research aims to shed light on the factors influencing wasp populations and the potential ecological consequences of their decline amid changing climate conditions.