Cornu aspersum, a hermaphroditic garden snail that injects sexual venom into its mating partner © Ronald Jenner

· New research calls for any species that manipulates the body of another organism by means of internally delivered toxins to be classified as venomous, for example snails, slugs and aphids

· Authors hope their redefinition will mean that scientists from traditionally separate fields can combine forces to accelerate understanding of venom biology and its applications

A new study released today shakes up the scientific understanding of venom and proposes a radical redefinition that means the saliva of aphids and chemicals released by slugs will join the bites of snakes and spiders to be classed as venomous.

According to the research these diverse substances all function with the same evolutionary function in mind: to manipulate another organism’s body against its interests.

The paper, led by Natural History Museum’s venom expert, Dr Ronald Jenner, and published today in the journal Trends in Ecology & Evolution, argues that venom should be redefined as any internally delivered secretion that one organism uses to produce a “negative extended phenotype” in another living organism - in other words, a physiological change in another living organism that benefits the venom producer at the recipient’s expense.

This definition was, in part, inspired by Richard Dawkin’s concept of the extended phenotype in his eponymous book published in 1982.

This means that insects such as cicadas, aphids and shield bugs who suck the sap of plants and inject toxic secretions to disable plant defences, and garden snails and slugs, which use toxins to manipulate their sexual mates, join the ranks of snakes and scorpions that use venom in predation.

Dr Jenner said, “This redefinition helps us understand venom not as a narrow weapon, but as a widespread evolutionary strategy. If you look at what the proboscis of a mosquito does when it’s in your skin, it injects toxins that suppress the immune system so that the animal can safely take a blood meal without being swatted away. On a molecular level it shows a lot of similarities to what happens when a viper bites, say, a bunny.

“Conceptually they work on exactly the same system: a conflict arena between two organisms that is mediated by injected toxins. And that’s venom.”

The study also finds that the earliest venoms in two of the most diverse venomous animal groups - Hymenoptera (wasps, bees, ants) and Hemiptera (bugs, aphids) - were originally used to manipulate plants, not animals. Animal-targeting venoms evolved later.

It also became clear to the researchers that this biological essence of venom could also be applied to animals that inject potential partners with toxins during sexual courtship, such as slugs and snails. Examples range from snails that shoot love-darts coated with bioactive molecules to manipulate their partners against their interest , to male blowflies whose barbed phallus injects a secretion that prevents females from mating again.

These sexual secretions, the researchers argue, also fit their definition of venom in that substances are internally delivered to manipulate a recipient in a conflict of evolutionary interests.

The researchers hope their redefinition will break down disciplinary silos in venom research. With this expanded definition of venom, researchers from traditionally separate fields can now recognise connections that exist between their areas of expertise boosting both theoretical understanding and new applications of venom biology. The latter could include applications in the pharmaceutical industry or in agriculture, as bioherbicides, an environmentally friendly way to control weed growth.

This research is part of the Museum’s Evolution of Life research theme that seeks to reveal the causes and consequences of evolutionary and environmental change which is central to understanding life on Earth.

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Images are available here.

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