Ontario cottagers may want to give oak trees some credit. It turns out they’re pretty adept at helping keep caterpillar infestations down.
According to a new study from researchers at the University of Würzburg in Germany, oak trees can fight back against hungry caterpillars simply by waiting a few extra days to leaf out in spring. The findings, published in Nature Ecology & Evolution, suggest that after a heavy infestation year, oaks delay budburst by roughly three days the following spring, which is just enough to prevent the newly hatched caterpillars from thriving.
The strategy works surprisingly well. Researchers found the short delay reduced caterpillar survival dramatically and cut leaf damage by about 55 percent.
“The delaying tactic is more effective for the oak than a chemical defense, such as bitter tannins in the leaves,” said lead author Soumen Mallick in a University of Würzburg press release. Producing chemical defenses requires significant energy from the tree, making strategic timing a more efficient option.
FAQ: Spongy moth caterpillars
The discovery also changes how scientists understand spring forests. Trees aren’t simply reacting to temperature and sunlight, they’re responding to biological threats as well.
To study the phenomenon, researchers monitored forests across 2,400 square kilometres of Northern Bavaria using Sentinel-1 radar satellites capable of seeing through cloud cover. Between 2017 and 2021, the team collected more than 137,000 observations, tracking how forests reacted after a major spongy moth outbreak in 2019.
“The radar sensors recorded exactly which trees were stripped bare and how they reacted in the following year,” said Jörg Müller, the study’s co-senior author.
The findings may also help explain why some forests don’t always green up as early as warming temperatures suggest. Trees are continually monitoring their own atmosphere; climate change encourages earlier leaf growth, while insect pressure pushes some species to hold back.
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