Richard Collins: Makes scents — weapons and warnings in nature
'weaponry' Have Skunks' Are Stripes Know Way Predators Of Letting They A
The ‘foul mart’, or ‘polecat’, is native to Britain but it isn’t found in Ireland. ‘Mustela putoris’, its biological name, translates as ‘the foul-smelling musk bearer’. If startled, this relative of the stoat and the pine marten releases an obnoxious smelly substance. However, it’s in the half-penny place compared to the stink its distant relative, the skunk, produces. It squirts a revolting vaporous fluid, the animal equivalent of a policeman’s pepper-spray.
As Looney Tunes devotees know, Pepé le Pew, the skunk, is frustrated in his search for love because of the pong he gives off. Like polecats, skunks produce their repellent substance in anal glands. It will see off predators as big as bears.
I came on a striped skunk in Vancouver’s Stanley Park some years ago. 'Don’t mess with it', I was told... 'give it a wide berth'. Exposure to the spray can cause vomiting and temporary blindness.
But there’s a downside to the skunk’s choice of weaponry — the animal can’t carry much smelly fluid. Following a few discharges, it is out of ammunition and needs several days to create more. Skunks, therefore, deploy their nuclear weapon only if they have no choice. Their powder is kept dry and enemies are warned in a propaganda war.
As with all weapons of mass destruction, deterrence is the name of the game. MAD, the doctrine of ‘Mutually Assured Destruction’, has kept an uneasy peace between East and West since the bombing of Hiroshima and Nagasaki in August 1945.
There is nothing new about deterrence. The social wasps use their loud buzzing and bright yellow stripes to warn off enemies. The measure is so effective that hover-flies, which can’t sting, mimic the wasp’s colour pattern. Trees create tannins to deter caterpillars from dining on their leaves. The poison absorbed by the caterpillars upsets the tummies of birds which eat them — ‘once bitten, twice shy’ is the order of the day. Touching water where an electric eel is lurking leads to a rude awakening.
Why are skunk stripes variable in some places but uniform in others? Our new paper in Evolution used 749 museum skins to examine several hypotheses for why an aposematic (warning) signal like stripes should be variable when having consistent stripes helps preds make fewer errors! pic.twitter.com/pXqYfu6mra
— Ted Stankowich 🦨🐆🦌🦔🦏🦡 (@CSULBMammalLab) October 6, 2023
There’s no point in developing a weapon of mass destruction unless you let your enemies know that you have it. The conspicuous black-and-white pelage of the striped skunk is the equivalent of our skull-and-crossbones nuclear hazard logo.
Using museum skins, Hannah Walker and colleagues at Bristol University examined the colour patterns of striped skunks across the species’ range. They found that "variation is huge across North America". In places where there were lots of potential predators, skunks wore their standard uniforms.
However, in areas with few predators, "skunks show very varied fur colours" — some are all black, or have a thin black-and-white bands. There were even all white individuals.
Why is there such a contrast between them and skunks living in high-predator areas?
Consistency, the scientists suggest, is necessary, so that predators learn to recognise the skunk pattern quickly and reliably. Educating potential predators is the name of the game; there must be no ambiguity, so everyone dresses alike.
Where there is little threat from predators, however, skunks can let it all hang out. Anything goes and a more permissive dress-code is tolerated.