Midge Fossils As Indicators of Past Climate Change

Fossil midges are quite common. Viktor Baranov (Ludwig Maximilians University, Munchen) has attempted to determine whether these cold-blooded invertebrates follow the 'Bergman Rule' (https://www.theguardian.com/science/2021/may/04/terrawatch-midge-fossils-offer-insight-into-past-climates). The 'Bergman Rule' is based on the observation that many warm-blooded species (e.g. bears), become larger when they live under colder conditions. This is because their surface area to volume ratio becomes lower. This means they are less likely to lose body heat (midges only warm up by basking). Baranov and his team found that non-biting midges became 1mm longer, for every 5 degrees in latitude, as one moved towards the North Pole. He consequently suggests (as they follow the 'Bergman Rule) they can serve as indicators of past climate change. At a particular latitude, an increase in the sizes of fossil midges, would indicate it was getting colder. Baranov's team looked at more than 6000 midges, dating from 245 million years ago to the present day. The results tentatively support their claim. The picture may, however, be complicated by male and female midges showing a sex difference in size. It is also not always easy to identify the precise species of a fossil midge.