Grasshopper size changes in response to shifting climate

As insect populations decline globally in a phenomenon some have described as an “insect apocalypse,” biologists are racing to understand how insects are reacting to climate change.

A recent study of Colorado grasshoppers provides valuable insights into this issue, particularly how their size has changed over time.

While the answers are not straightforward, researchers believe they already possess much of the knowledge needed to make predictions about which species will thrive and which will struggle in the long term.

The findings stem from the rediscovery of 13,000 grasshoppers collected between 1958 and 1960 by a biologist at the University of Colorado Boulder.

After the scientist’s death in 1973, his collection was preserved by his son and eventually donated to the CU Museum. It remained untouched until 2005 when César Nufio, then a postdoctoral fellow, stumbled upon it.

Recognizing its potential, Nufio began curating the collection and revisiting the original sites to gather new specimens.

Grasshopper size in changing climate

Nufio and his colleagues, including Caroline Williams, Lauren Buckley, and Monica Sheffer, analyzed how six species of grasshopper had changed in size over 65 years.

Since insects are cold-blooded and rely on external temperatures for development, their growth is highly sensitive to environmental changes.

Contrary to the assumption that animals might shrink to reduce heat stress, some grasshopper species actually grew larger over time. These species benefited from an earlier spring, allowing them to feed on fresh vegetation.

However, this advantage was limited to species that overwinter as juveniles, known as nymphal diapausers. These grasshoppers could take advantage of early spring conditions to grow faster.

In contrast, species that hatch from eggs laid in the fall – egg diapausers – did not fare as well. As vegetation dried up earlier in the season, these species became smaller over the decades.

“This research emphasizes that there will certainly be species that are winners and losers, but subgroups within those species populations, depending on their ecological or environmental context, will have different responses,” noted Sheffer.

Predicting winners and losers

The researchers based many of their predictions on the life cycles of the grasshoppers and the environmental conditions of the study site.

By reviewing existing knowledge about the species’ natural history and elevational gradients, they were able to anticipate some of the observed trends.

“We sat down and looked at all that was known about the system, such as elevational gradients and how that should modify responses and how different grasshoppers might respond, with all the wealth of information we knew about their natural history. And while not all our predictions were supported, many of them actually were,” explained Williams.

Understanding which species will succeed or fail in a changing climate has been a significant challenge. According to Buckley, this study offers principles that could improve future predictions and help address ecosystem changes caused by climate change.

Historical data on grasshopper size

The grasshopper collection was originally assembled by entomologist Gordon Alexander during three summers in the late 1950s. He meticulously documented the timing of six life stages of the grasshoppers, creating a detailed record.

After his untimely death in 1973, the specimens were stored away until Nufio rediscovered them in 2005. Recognizing their value, he initiated a resurvey of the same areas, ultimately collecting around 17,000 new specimens.

Museum collections like Alexander’s have proven invaluable for studying climate change‘s long-term effects.

For example, Joseph Grinnell’s surveys of California wildlife from 1904 to 1940 provided a baseline for comparing changes a century later. Similarly, Nufio’s work highlights the importance of preserving historical data for modern research.

Grasshopper size changes across elevations

The researchers focused on short-horned grasshoppers from the Acrididae family, categorizing them based on their life cycles.

Nymphal diapausers, which mature as early as May, grew larger at lower elevations. In contrast, early and late emergers from overwintering eggs decreased in size over the decades at these elevations.

“For those that come out in late August, when it’s very crispy and dry and we get very hot temperatures, we saw the most negative impacts of climate change,” Williams noted.

Surprisingly, none of the species increased in size at higher elevations, despite greater summer warming in these areas. This may be due to snow delaying early-season plant growth, reducing food availability.

The findings align with experiments where grasshoppers were caged at various elevations to study their adaptation to heat and dryness.

Broader implications of the research

The study’s results suggest that some grasshoppers can benefit from warming by growing larger and emerging earlier, while others face stress and shrink in size. Similar trends have been observed in other insects, such as butterflies, according to Buckley.

“We find a pretty similar message with butterflies, which is hopeful to me, in that if we can consider some basic biological principles, we really increase our ability to predict climate change responses,” she said.

The team plans to continue exploring the metabolic, biochemical, and genetic factors driving these size changes.

“Using those museum collections allowed us to go back in time to compare exactly the same sites – there hadn’t been any changes in the land use over this 60-year period of warming – using exactly the same methodology,” said Williams.

“Having those unique historical specimens enabled us to look at the changes through time.”

This study highlights the complexity of predicting climate change impacts on ecosystems and highlights the critical role of long-term data in unraveling these challenges.

The study is published in the journal PLOS Biology.

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