150 years on, scientists have confirmed Darwin’s hypothesis about carnivorous plants

Saxifraga candelabrum grows at altitudes of between 2,500 and 3,300 metres in south-western China. The plant has to survive in rock crevices where nutrients are scarce.

Its stems and branches are covered in sticky hairs. It is mainly small midges that get stuck to them. After studying the plants in the wild, scientists discovered that, on average, a single adult specimen had 71 trapped insects.

Traces of prey were also found on 43 out of 45 museum specimens studied. This showed that the flower catches insects constantly, rather than occasionally or by chance.

Details

The scientists investigated exactly what attracts insects to the plant. Some of the flowers were covered with a transparent hood, which prevented the scent from spreading. Other plants were covered with a mesh that restricted their visibility.

When the scent was blocked, insects flew in noticeably less frequently. The researchers believe that the scent of the flowers helps the plant to lure potential prey.

However, large flies and bees, which pollinate the plant, did not usually get stuck to the hairs. The trap is designed primarily for smaller insects. Thanks to this, the flower can simultaneously obtain food and retain its pollinators.

The key evidence came from the nitrogen in the flies

The mere fact that insects are captured is not enough to classify the plant as carnivorous. It must be able to digest its prey and utilise the resulting substances.

Scientists discovered a substance on the sticky hairs that helps break down the insects’ bodies. The flower was then fed fruit flies in which the nitrogen had been labelled with a special, harmless tracer.

Later, this nitrogen was found inside the plant, particularly in the flowers and fruits. In the ordinary plants used as controls in the experiment, no such transfer occurred. The researchers also tested the soil and ruled out the possibility that the labelled nitrogen had been absorbed through the roots.

This confirmed that the sundew does not simply catch flies, but actually uses them as an additional source of food.

What exactly did Darwin predict?

In his book on insectivorous plants, published in 1875, Charles Darwin drew attention to the sticky hairs of two other saxifrages — Saxifraga rotundifolia and Saxifraga umbrosa. He suggested that these plants might feed on insects, but the experiments available to him did not provide a conclusive answer.

The new study focuses on another species of the same genus. Consequently, the scientists have confirmed Darwin’s general hypothesis regarding carnivorous saxifrages, but have not proven that the specific species he studied actually digest their prey.

Why this discovery surprised scientists

Most known carnivorous plants inhabit marshes and damp areas with poor soil. Saxifraga candelabrum, by contrast, grows in dry, high-altitude regions.

It does not look like a Venus flytrap or a plant with large pitcher-like traps. Its weapon is its almost invisible sticky hairs. These probably originally served to protect the flower from herbivorous insects, but later evolved into a means of hunting.

A comparison of genes has shown that the saxifrage and other carnivorous plants have independently developed similar adaptations related to the capture, digestion and assimilation of prey. However, the role of individual genes still needs to be verified through further experiments.

Why this is important

The discovery shows that carnivorous plants may be far more diverse than previously thought. Some seemingly ordinary flowers with sticky leaves or stems may not simply be defending themselves against insects, but using them as a food source.

That said, the study does not prove that all saxifrages are predatory. So far, a complete body of evidence has been obtained only for Saxifraga candelabrum.

Source

Study: Xin-Jian Zhang et al.

Identification of carnivory in the flowering plant Saxifraga via multidisciplinary evidence.

Journal: Nature Communications, 2026.