Swiss wasp nest reports jump fivefold in five years, but experts debate real increase

Reported nests surge

Mobiliar insurance data shows a fivefold increase in reported wasp nests during July and August over five years. The frequency rose from 0.27 cases per 1000 households in 2021 to 1.34 in 2025. Nationwide, policyholders reported around 5800 nests last year. Mobiliar spokesperson Robin Locher said that as of late July 2026, the insurer had already incurred more damage costs than in all of 2025, with one to two hot months still ahead.

“As of today, we already have more damage costs than in the entire last year.”

20210.27

20251.34

2021

0.27 nests/1000 households

2025

1.34 nests/1000 households

Data from the article text

Regional hotspots

The French-speaking Romandie region recorded the highest density in 2025, with 2.5 nests per 1000 households, followed by German-speaking Switzerland (1.08) and Ticino (1.04). Canton Jura stood out with an eightfold jump in reports over the five-year period. The insurer noted that regional differences can be large, with the fewest reports last year coming from Nidwalden, Glarus, Basel-Stadt and Graubünden.

Romandie2.5

German-speaking1.08

Ticino1.04

Romandie

2.5 nests/1000 households

German-speaking

1.08 nests/1000 households

Ticino

1.04 nests/1000 households

Data from the article text

Climate and insect decline drive visibility

Biologist Fabian Klimmek of Bern Animal Park Dählhölzli attributes the rise to mild winters and dry springs, which help queens overwinter and start colonies early. Insect decline also pushes common and German wasps toward human food. Pest controller Thomas Iseli explained that drought eliminates puddles and mosquitoes, depriving wasps of their natural prey.

“When we barbecue and eat a steak, we either have to share it with the wasp or you have wasps around the table the whole time.”

Heat waves add stress: wasps cannot sweat, so they need more energy and become more aggressive in foraging, Klimmek noted.

“Unlike humans, the wasp has no natural air conditioning - it doesn't sweat. In heat, it needs more energy. That's why wasps are more aggressive in searching for food at high temperatures and are more likely to sting.”

Experts question the trend

Not all scientists see a genuine population boom. Hannes Baur, an insect expert at the Natural History Museum Bern, said there is no systematic monitoring of common and German wasp populations. He believes the increase in reports likely reflects changes in human behavior and insurance claim recording rather than more wasps. The 2021 baseline was an unusually wet year with few wasps, making the comparison misleading.

“I have the impression that there are always about the same number of wasps.”

Seraina Kopfstein, a biologist at the Natural History Museum Basel, also cautioned that the fivefold figure may be exaggerated, though she acknowledged that climate change is enabling earlier colony growth. She added that extreme heat and heavy rainfall can destroy entire nests.

“We will have to live with the fact that we see more wasps.”

Ecological benefits and safety tips

Despite their nuisance, wasps play a vital ecological role. Klimmek stressed that they pollinate plants, provide food for birds, and naturally regulate insect pests. Other wasp species are not interested in human food and are mostly peaceful. The Mobiliar advises covering food and drinks outdoors, clearing leftovers quickly, and avoiding drinking from unattended cans or dark bottles. The most effective tip, experts say, is to remain calm and avoid swatting.