The recent heat wave and its effects on bees

This winter’s unusually high temperatures are threatening the lives of bees and other pollinators.

Between February 2023 and January 2024 the average global temperature increased by 1.52°C: global warming exceeded the 1.5°C limit for the first time over the course of an entire year and January 2024 was declared to be the warmest ever recorded globally, according to what emerges from Copernicus data, the Earth observation program of the European Space Agency (ESA) and the European Commission.

Coldiretti, the Italian organization of agricultural entrepreneurs, active at both national and European level, recently monitored the consequences of the recent excessively mild winter. Among other effects, this unseasonal heat is threatening bee health. As a result, honey production is compromised, as well as the yield and quality of three out of four food crops (75%), which depend to a good extent on bee pollination.

Knowing there will be no sources of nourishment for them in nature throughout the whole winter, bees manage to survive thanks to the supplies of honey and pollen they accumulated in summer and autumn. Due to the freezing wind and low temperatures, bees choose to stay inside the hive, where they can overcome the cold by warming each other. For this purpose, bees gather in a strategic formation, called glomere, that keeps themselves and the queen warm. The queen bee, in the meantime, gradually decreases egg-laying, until it stops completely, going into brood block. Bees stay in this survival formation until the first days of spring sun.

However, this year the first warm days arrived suddenly and earlier than they should have, tricking the bees into thinking it was already spring. When the bees felt the temperatures growing, they started to forage. In the hottest hours, they would begin to go outside the hive looking for flowers. However, the situation they found was very different from their expectations: they found little to no floral resources in nature. Furthermore, foraging is a lot of effort for the bees, and they can not recover from it because there is no pollen for them to collect.

Under the circumstances, beekeepers are forced to intervene by supplementing the hives’ supplies with candied fruit, a naturally sugary substance that nourishes and strengthens bees, who however risk significant losses.

The worker bees, who leave the hive during the hottest hours, risk freezing to death when drastically lower temperatures surprise them outside the hives, at sunset. Moreover, the arrival of fresh pollen into the hive is usually a signal for the queen that it’s time to start laying eggs again. Brood rearing is essential for the hive: it takes place strategically at the end of winter and allows the swarms to get to spring with a good quantity of worker bees, so they can make the most of the first important blooms. If worker bees bring no pollen to the hive, the early breeding does not start, and poor or late brood heavily affects the consistency and strength of hive families.

The fear of beekeepers and experts is that the mild temperatures of the last period are nothing but a temporary heat wave, and that winter will return in March, harsher than before. In this case, wind and frost would be very harmful to the blooms and the well-being of the hives.

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