Why Do Hedgehogs Self Anoint?

Hedgehogs are ancient and exotic creatures with a unique appearance and some pretty outlandish behavioural traits. Perhaps top of the list of wired and wonderful hedgehog behaviour is the practice of self anointing. This week we are going to look at what self anointing is, when it happens, theories of why it happens and whether it is in any way harmful.

What is Self Anointing in Hedgehogs?

So Mr Hog (self anointing is much more common in males than females) will be going about his business then stop in his tracks and start chewing. He'll then begin foaming at the mouth and flicking this foamy spit over his back and shoulders. 

To reach the more difficult bits, he will bend into all sorts of weird shapes and use the underside of his tongue to spread the saliva over all his spines. 

This process might last a couple of minutes, or it might go on for up to an hour. 

It is pretty alarming the first time you see it. First the foaming at the mouth, then the contortions make it look like the hedgehog is having some kind of a fit. But actually, it's normal, if not that common, behaviour.

Take a look at this video for a live demo.

Hedgehogs are totally absorbed in what they are doing whilst self anointing, It's almost like they are in a trance. When they finish, they often seem dazed or tired according to Marc Baldwin or Wildlife Online. The hedgehog is very vulnerable to predators during and for a while after the anointing. So we have to assume it has (or had in the past) a vital function. 

What Triggers Anointing?

Anointing is generally thought to be triggered by a strong or unusual smell. Whisky, cigarette buts, paint and leather, will all set hedgehogs off. But then as Pat Morris notes in his book Hedgehogs so can distilled water. 

Self anointing was once thought to be courtship or sexual behaviour that only happened during the mating season. But it has now been found to occur at all times of the year. 

It can happen when the hedgehog is alone, when it is with a mate, or when mother and hoglets are in the nest together. 

Like much to do with self anointing triggers for the behaviour are not really understood.

Do All Hedgehogs Self Anoint?

Self anointing turns out to be a pretty uncommon behaviour. Pat Morris quotes a Belgian study which found only 2% of hogs with fresh saliva on their spines. 

Wildlife Online reports the same study showing that males are far more likely to self anoint than females and that the behaviour is more common in juveniles than adults. 

There is also some seasonality to the behaviour. The peak of anointing was observed by the Belgian study in July. There was a fall-off in August and a resurgence in September. 

There doesn't seem to be much of a pattern here to give us clues about the purpose of the behaviour.

Are Hedgehogs the Only Animals That Self Anoint?

This behaviour has been recorded in all branches of the hedgehog family around the world. 

And hedgehogs are certainly not the only species who self anoint. The behaviour has been recorded in several species of monkey, in deer and in giant pandas to name just a few. 

But observation of these species doesn't bring us any closer to understanding what purpose the behaviour serves. 

Why Do Hedgehogs Self Anoint? 

Well, the truth is we don't know, we have only theories. But let's take a look at some of them. 

Sexual Scenting?

An early study by Robert Brockie based on observation of European hedgehogs in New Zealand proposed that the behaviour might be sexual. The hedgehogs used self anointing to distribute their scent and attract potential mates. 

But the Belgian study records the peak of activity in July when breeding peak season is actually April and May. So this doesn't seem like a likely explanation. 

Toxic Spit Syndrome?

Some insectivores, like shrews, have saliva that is toxic and can be used to poison and subdue the insects they eat. 

So it was thought that the same might be true of hedgehog saliva and self anointing was a way of spreading the poison to the spines aa a grooming process to kill fleas and other parasites.

However, subsequent research has shown that unlike other insectivores hedgehogs saliva doesn't contain toxic elements. And the activity would need to be done much more regularly to form a useful part of the grooming process. 

Poisoning Predators?

Whilst we're on the subject of toxins and poisons, there is another theory we can look at. 

Hedgehogs are notoriously resistant to poison. They can eat toad skin and withstand snake bites. 

So It has been argued that chewing on poisonous substances triggers the self anointing, which then produces toxic saliva, which is smeared over the spines to act as a further deterrent to predators. 

A 1977 study by Edmund Brodie took hedgehog spines self anointed by hogs who had chewed cane toad skin and jabbed them into the arms of volunteers. 

This caused an immediate and irritation and burning not present when the subjects were jabbed with a control set of "clean" spines. 

So self anointing after chewing on something toxic can certainly produce "irritant" spines, that might act as a further deterrent to predators. 

But there are a few problems with this theory. 

First, self anointing isn't just triggered by chewing on toxic substances, as we've seen it can be triggered by things as innocuous as distilled water or mother milk. These aren't going to produce saliva that would cause predators any problem.

The second point is that, with all those nice sharp spines on board, and the ability to ball up, does the hedgehog really need any more defences?

The Camouflage Theory

The camouflage theory seems entirely plausible though no research exists to back it up. 

This theory supposes that hedgehogs self anoint to cover their own scent and disguise themselves from predators and other, competitor hogs. 

This makes some sense. Males self anoint more than females and males range over a wider area and can be highly aggressive towards one another. Juveniles anoint more than adults, and this could offer them some protection at a vulnerable stage of their lives. 

The Scent Signalling Theory. 

Both Pat Morris and Marc Baldwin think the behaviour could be some kind of scent signalling. 

They both note that the spines create a large surface from which the saliva and any odours or pheromones it contains can evaporate into the air. 

This could be signalling to other hedgehogs: either "come hither and mate with me" or "get out of my patch" or "hey, we're related!"

It's just a theory at the moment, and clearly, more research is needed, but it seems like an interesting idea.

Of course, the final option is that the self anointing is just a non-adaptive behaviour. Something that used to have a purpose at an earlier time in the hedgehogs 15 million year history has ceased to be useful now but is still done on auto-pilot, as it were.

The truth is we just don't know.

Is Self Anointing Harmful to Hedgehogs?

Although anointing looks alarming, it's a natural behaviour and is not a sign of illness or distress. 

The total absorption in the behaviour and dazed state afterwards can leave hedgehogs vulnerable though. 

There has been some concern that self anointing with noxious or poisonous substances, like toad skin, and even famously dog poo, could poison the hedgehog. But as we've seen, hedgehogs are resistant to poisons and toxins, and there seems to be no evidence that this could be a problem.

All Part of the Mysterious World of the Hedgehog

From its strange appearance to hibernation, defensive balling and now self anointing there is so much we don't understand about the hedgehog. 

He has been fully evolved into his modern form for so many millions of years that he possesses characteristics that don't exist in many other modern mammals. Who knows what secrets he holds for science, medicine and ecology?

This is just one of the reasons why preserving our hedgehogs is so important - as if their general cuteness wasn't reason enough!

We hope you've enjoyed this weeks post and found it interesting. If you have self anointing stories or questions to share, we would love to hear them. Leave us a comment below.