Why am I seeing bumblebees around aphids?

Each year, people get in touch to ask why they are seeing bumblebees visiting curled up leaves on flowerless hedges and trees.

These plants are often home to aphids, commonly known as blackfly or greenfly. These little insects feed on the sap of the plants and as a result produce lots of sticky sugary waste – honeydew. Aphids are good at what they do and can be found in big numbers, which attracts other animals to feed on the honeydew or the aphids themselves. The best example are ants, which go as far as to protect aphids from other predators and essentially farm them for the sweet liquid they produce. If they discover it, bumblebees will also feed on the honeydew, which provides them with energy, in a similar way to nectar.

What is really interesting is that many of the gardens that people witness this behaviour in are full of bee-friendly flowers, which indicates that bumblebees are sometimes choosing to consume honeydew over nectar. Bumblebee nest success is all down to energy-economics and bumblebees naturally attempt to collect food as efficiently as possible, so it may be that during these aphid booms there is an easier, larger or more energy-rich fast-food on offer in the form of honeydew that bumblebees can take advantage of.

The one thing that honeydew cannot replace however, is pollen from flowers, which provides the protein for growing larvae into adult bees. So, it’s unlikely that we will see bumblebees switching from flower foraging to aphid farming any time soon.