On the BBC Radio 4 programme 'The Unbelievable Truth' recently, the claim was made that "hedgehogs will die without their fleas". This, if true, is remarkable. How could a mammal depend directly on fleas, and what would happen to the dear little hogs if deprived of their fleas?

Is there any truth in it, or was the BBC a bit wide of the mark?

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Of course, it's nonsense. Hedgehogs do not die without their fleas - how could they? in fact, not all hedgehogs have fleas at all as the British Hedgehog Preservation Society confirms.

It's possible that having fleas could benefit the race of hedgehogs - although not necessarily the individual hedgehogs - by boosting their immune responses, as fleas are passed on from the mother hedgehog, and conceivably her fleas could help keep her children immune to diseases. However that's pure speculation.

More interesting is the hedgehog flea itself, Archaeopsylla erinacei. Long legged, the flea is able to run about between the widely-spaced spines - unlike human, cat and dog fleas which tend to cling onto the much shorter and more closely-spaced hair and fur. The website CRASH (Care Rehabilitation and Aid for Sick Hedgehogs) says this:

Hedgehog fleas only live on hedgehogs. They like the cool open environment of the coarse and widely spaced spines where it can run fast. If it finds itself in the dense, warm coat of a dog or cat, it immediately knows it's in the wrong place and drops off to wait for another hedgehog. The same goes for hedgehog fleas that get onto humans, they do not stay long before leaving to find a proper host.

One of the most often-repeated statements about fleas on hedgehog welfare sites is that hedgehog fleas are specific to hedgehogs, so our pets - and ourselves - are safe from them. Unfortunately, whilst generally the case it is certainly not always true. For a start hedgehogs often carry fleas from other animals, but even their own specific flea turns out to be a bit more catholic in its taste than is generally suspected. A quick look at the Natural History Museum's Distribution of British fleas catalogue (go on, bookmark it, you know you want to) shows a sample of the hosts that A. erinacei has been found on. Erinaceus europaeus is the hedgehog - so that's OK - but we also get foxes, rabbits, moles, polecats, dogs, cats, dormice (both native and edible), red squirrels, hares and even a human. And just to add insult to injury, there's definitely at least one recorded case of a hedgehog flea attacking a human... it's not recorded whether or not this was a very spiny individual.