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Some black and yellow-striped picnic visitors might be smaller than their ancestors were a century ago. At least one common wasp species appears to be shrinking as a consequence of the ongoing global rise in temperatures caused by climate change.

Warming-driven shrinkage has already been documented in vertebrates—like antelope and sparrows—and may be caused by stress from heat or changes to food availability, or even the relationship between body size and heat retention. But climate change’s impact on insect body size is poorly understood.

When Carlo Polidori—an entomologist at the University of Castilla-La Mancha, Spain—and his colleagues came across the many decades of insect samples at Madrid’s National Museum of Natural Sciences, they saw an opportunity to see how insects’ bodies have changed over time.

The team measured the body size, head width, and wing size of over 200 tree wasps (Dolichovespula sylvestris) in museum collections. These specimens came from various locations on the Iberian Peninsula, and some dated back to as early as 1904.

They found that the wasps got smaller over time. Comparing their data with Iberian climate records, they found that this decline in size correlated with rising temperatures. The team can’t be sure of causation, but such shrinking in insects may be tied to their early development, which speeds up in hotter temperatures and can produce smaller adults.

Smaller wings

A handful of other studies have revealed climate change-driven shrinkage of other insects, like beetles, but this is the first study to show such an effect in a social, colony living species. Such social insects have sophisticated control over the temperatures of their hives, but the results suggest that even these species may be susceptible to climate change.

“Body size shrinking is likely to have some adverse effects on recent (and future) insects,” says Polidori. “For example, smaller wasps may be able to hunt only smaller prey species compared with past wasps.”

Oddly, the wasps’ wings are shrinking faster than the rest of their bodies, and if changes to the wing shape aren’t occurring as well, Polidori expects modern wasps could be less agile and speedy in flight.

Jessica Forrest, at University of Ottawa in Canada, notes that environmental factors other than temperature may be the direct driver of wasp shrinkage.

“If prey insects are on average getting smaller, wasps could have evolved a smaller body size over the last century,” says Forrest.