Oak Trees Delay Leaf Emergence by Three Days After Caterpillar Infestations, Study Finds

Oak trees infested by caterpillars open their leaves three days later the following spring, a delay that halves the amount of leaves eaten by the insects. Soumen Mallick and colleagues at the University of Würzburg analyzed tree canopy conditions using Sentinel-1 radar satellite images. Their work covered a 2400-square-kilometre area in northern Bavaria, Germany, from 2017 to 2021.

The forests there are dominated by pedunculate oak (Quercus robur) and sessile oak (Quercus petraea). Each pixel in the satellite images represented a 10 by 10 metre area. The team examined 27,500 pixels in total.

In 2019, a massive outbreak of gypsy moths (Lymantria dispar) occurred in the area. The gypsy moth caterpillars feed on tree leaves. Oak trees heavily infested in 2019 had leaves emerge three days later in spring 2020 than non-infested trees.

This delay reduced leaf damage by 55 percent compared to the previous year. Caterpillars hatch at the same time regardless of the delay. 1038/s41559-026-03071-9.

Mallick stated that the delay in bud opening seems more efficient than other oak defenses, such as making leaves tougher to chew or producing aromatic compounds that attract predators to the caterpillars. He thinks other deciduous plants may exhibit similar responses.

James Cahill at the University of Alberta called the finding plausible but noted that the delay correlates with outbreaks, and evidence of causality requires more data from additional events.

Cahill suggested the delay could stem from decreased plant vigor after leaf loss, though data from more than one outbreak would clarify the mechanism. James Blande at the University of Eastern Finland described the mechanisms as intriguing and in need of further research.

Mallick explained the delay could result from physiological constraints like resource depletion, but its consistency across dozens of tree populations—strongest where it most effectively reduced herbivory—points to an adaptation rather than just an individual tree's response.

The discovery also accounts for why forests sometimes turn green later in spring than climate models predict, especially as warming alters temperatures. Mallick emphasized that plants respond to factors beyond climate change alone. Cahill agreed, stating this point is very important.

In other news, Elon Musk spent three days on the witness stand this week in his lawsuit against OpenAI. The lawsuit occurred in the week of May 1, 2026. Emails, texts, and Elon Musk's tweets are being presented as evidence in the lawsuit.

Elon Musk argues that OpenAI's conversion to a for-profit model betrayed the nonprofit mission for the benefit of humanity. " Sam Altman is the CEO of OpenAI. On April 26, an unspecified event was scheduled in three days.

On May 2, the unspecified event was scheduled for next week.