Source: Wild Hogs Hedgehog Rescue
Unfortunately, I have never had the opportunity to see a hedgehog licking its own quills, but I know that if I did, this would be my reaction. As a matter of fact, I thought these exact words when I saw a video of a hedgehog self-anointing.
But what is self-anointing? Does it mean that hedgehogs actually lick themselves?
The term was coined by Maurice Burton in an article for New Scientist in October 1958. In fact, the first person to observe this behaviour was the German zoologist Ludwig Heck, who in 1912 called it 'selbstbespuchen', self-spitting in English. This bizarre behaviour consists mainly of a hedgehog covering its spines with a frothy saliva-stimulant mixture as if the animal were almost licking itself. This behaviour seems to be triggered by objects with particular odours or which the animal has never had to deal with before, which are often sniffed, licked and chewed, thus producing a special saliva that is applied to the hedgehog's quills and fur. Sometimes just the smell is enough to trigger self-anointing. Perhaps the most curious aspect of self-anointing is the fact that to date it is still not entirely clear to researchers in this field what the reason for this bizarre behaviour is. The main difficulty scholars have encountered in determining a plausible explanation for self-anointing is that it appears to be an individual-specific behaviour, or at least one that is subject to variation because objects that stimulated the behaviour once may not do so later.
Source: Yuhan Chang, Unsplash
A first theory suggests that hedgehogs would self-anoint in front of pungent or acrid smelling objects, but this is contradicted by the fact that the behaviour has been observed in hedgehogs presented with distilled water which has no smell or taste and by the fact that some pungent and/or acrid substances such as petrol, vinegar and whisky do not seem to induce it. The idea that hedgehogs self-anoint when in contact with objects new to them also seems to be disproved. As a matter of fact, the behaviour has been observed when stimulated by objects such as grass and substances such as rainwater and milk, which are hardly foreign to animals like hedgehogs. Another theory is that they use self-anointing to mask their odour in order to deter predators and protect themselves from other hedgehogs, especially males, as they can become very aggressive. However, this theory is not particularly convincing because many of the substances that stimulate self-anointing would fail in repelling predators. Furthermore, there are no studies that explain this behaviour in females, unless it is assumed that they only practice it when they do not want to deal with males. It has also been suggested that self-anointing could serve to add an irritation factor to the quills that would result in chemical trauma to any potential predator. Although this seems a plausible explanation, it is very likely that any anti-predator effect is pure coincidence.
According to some researchers, this behaviour could instead be linked to the need for spines to be groomed. In reality, there is no evidence showing the fundamental role of saliva produced during self-anointing in this process, nor the need for hedgehogs to actually groom their quills in order for them to remain supple, not least because they are constantly replaced.
Source: Hans-Olof Andersson, Unsplash
Some researchers think that self-anointing may be a non-adaptive behaviour, i.e. an aberrant activity that did not evolve to increase the chances of survival. This could be true but is very unlikely as hedgehogs are completely absorbed during anointing, making them very vulnerable to predators. In addition, it has been observed that they are often tired and hungry afterwards, suggesting that it could be very energy-intensive, which would not be beneficial if it were a non-adaptive behaviour. Given that hedgehogs are fairly ancient creatures, however, having been around for around 20 million years, it is possible that self-anointing may have served some important purpose for their ancestors. The most popular theory is the one according to which self-anointing plays a role in scent-marking, perhaps involving the vomeronasal organ, that we have yet to understand though. Even though a true explanation of this peculiar behaviour remains to be discovered, it seems clear that it must have some adaptive function or have done so in the past.