Garden slugs and snails could now be considered venomous, study finds
In a study that shakes up the definition of venom, researchers explain it is not just the bites of snakes and spiders that are classed as venomous, but also the saliva of aphids and the chemicals released by slugs.
This change in definition will mean that tens of thousands of additional species could now be considered venomous.
According to the research, published in the journal Trends in Ecology & Evolution, substances like saliva all function with the same evolutionary function in mind: to manipulate another organism's body against its interests.
The paper, led by the Natural History Museum's venom expert Dr Ronald Jenner, argues that venom should be redefined as any internally delivered secretion that one organism uses to make a physiological change in another living organism.
This means that insects such as cicadas, aphids and shield bugs - which 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 on prey.
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.'
Researchers also found the venom in wasps, bees and ants, as well as bugs and aphids, were originally used on plants rather than animals.
Slugs and snails also inject potential partners with toxins during sexual courtship. 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 because substances are internally delivered to manipulate the recipient in a conflict of evolutionary interests.
The authors hope this redefinition could mean that scientists from traditionally separate fields can combine forces to accelerate understanding of venom biology.
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