Scientists have found that centipedes can alter the toxicity of their venom.

Millipedes are a large group of arthropods, comprising approximately 12,000 species, including the centipede Scolopendra morsitans. Having emerged on our planet over 400 million years ago, these creatures were among the first to actively use venom to immobilize their prey—crickets, cockroaches, and other small animals. However, millipedes can also fall victim to predators, which is why they require venom for protection.

To further investigate the toxic "arsenal" of S. morsitans, scientists from Queensland University (Australia) collaborated with colleagues from the University of Oslo (Norway). Their joint article was recently published in the journal Nature Ecology & Evolution.

In addition to the conventional method of venom extraction, which involved eliciting secretion through electrical stimulation, the researchers employed another technique. They prompted the centipedes to sting a paraffin-coated tube, simulating an attack on them. Subsequent experiments and toxin analyses revealed that the venom collected in different ways varied significantly.

In particular, tests on crickets showed that both types of venom resulted in paralysis of the insects. However, when tested on a laboratory model using sensory neurons from vertebrates (rats and mice), it was found that the second type of venom, produced by the centipedes during defensive situations, triggered a pain response in the receptors.

The scientists then dissected the venom glands and analyzed the remnants of the toxins contained within them after tests in which they encouraged the centipedes to attack prey and defend against attacks. Liquid chromatography coupled with tandem mass spectrometry confirmed that the secretion of venom for defensive and predatory purposes led to changes in the composition of the toxins.

In their search for mechanisms that allow S. morsitans to control venom secretion, the researchers took electron microscope images of the venom glands. They were able to identify two types of secretory cells. In the first type, the release of substances occurred during the contraction of surrounding muscles, while the second type reacted to chemical signals from hormones and neurotransmitters such as serotonin. This dual-level system enables centipedes to selectively activate different combinations of toxins and produce the necessary type of venom depending on the situation.

According to the scientists, such a mechanism may have evolved in millipedes as a strategy to avoid vulnerability after depleting their venom reserves, which replenish slowly. The "defensive" combination of toxins induces a more painful reaction, allowing them to deter other predators in the event of a potential attack.

Commenting on the new study for The New York Times, zoologist Michel Dugon from the National University of Ireland in Galway, who was not involved in the research, stated that the findings of his colleagues are both impressive and somewhat frightening.

It remains unclear whether other venomous animals can alter the composition of their "toxic cocktails." Nonetheless, the feature discovered in centipedes suggests that data from many past studies may be incomplete, the scientist noted.