While mosquitoes are usually noticed for their attempts to draw blood from humans, chironomids – commonly known as non-biting midges – typically feed on algae and small aquatic invertebrates. These insects have also proven to be valuable tools for scientists studying past climates. Chironomid larvae live in lake sediments, from which they can be collected and identified. Each species prefers to live within a specific range of July air temperatures.

An international research team, including Professor of Geology Siim Veski and doctoral researcher Varvara Bakumenko from Tallinn University of Technology, analyzed modern chironomid communities and their associated temperature ranges. Based on this analysis, they developed a mathematical model linking each species to its preferred temperature range. "This model can be used with fossilized chironomid collections to reconstruct past temperatures," Bakumenko explained.

The method complements existing techniques and fills a gap in climate reconstructions for Estonia, Latvia and Lithuania, as the model provides the most accurate possible reconstructions of July temperatures in this region. "This, in turn, significantly improves our understanding of historical climate changes and their impact on regional ecosystems," added the junior researcher.

According to Bakumenko, similar models have already been successfully used in Switzerland, Norway and Canada. However, the models' accuracy is greatest in areas where chironomid larvae are collected, making a separate study of Baltic-region chironomid distribution essential for creating reliable reconstructions of July temperatures for Estonia, Latvia and Lithuania.

The research team collected samples from 35 lakes in Estonia, Latvia and Lithuania and combined these with existing Finnish and Polish datasets. This effort resulted in the creation of a regional database for the Finland-Baltic-Poland area, encompassing data from a total of 121 lakes. "This extensive dataset covers a broad geographical and temperature range, making the model both reliable and precise. The new model reconstructs July air temperatures with an exceptional accuracy margin of just 0.7 °C," Bakumenko emphasized.

The study revealed that the distribution and ecological preferences of chironomids in this region differ somewhat from those found in Central and Northern Europe, highlighting the uniqueness of local ecosystems and their conservation importance. "Using chironomids as natural thermometers advances scientific understanding and underscores the need to protect our planet's diverse ecosystems, especially in light of ongoing climate change," the junior researcher said.

The article was published in the journal Boreas.

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