Hedgehog Facts & Trivia: Spines, Sleep and Decline

• An adult European hedgehog carries around 5,000 spines, which are hollow, made of keratin, grooved to save weight, and grown from ordinary hair follicles.
• Hoglets are born with their spines already grown, but sealed under a fluid-filled membrane that protects the mother during birth; it shrinks within a day to reveal about 150 soft white prickles.
• Hedgehog spines may have evolved as shock absorbers for falls rather than as anti-predator defence - hedgehogs climb walls and trees, then get down by rolling up and dropping.
• The oldest known mammal with defensive spines is Pholidocerus, an extinct relative of hedgehogs that lived more than 40 million years ago.
• In hibernation a hedgehog's heart rate falls from about 190 beats per minute to roughly 20, body temperature drops from 35C to 10C or less, and it breathes about once every few minutes.
• In October 2024 the IUCN moved the Western European hedgehog from Least Concern to Near Threatened, on evidence of declines approaching or exceeding 30% in ten years across much of its range.
• Surveys in Denmark and Sweden found up to 60% of hedgehogs carry mecC-MRSA, and genetic dating published in Nature in January 2022 traced that methicillin resistance back around 200 years - long before antibiotics were used in medicine.
• That resistance evolved because the bacterium shares hedgehog skin with the fungus Trichophyton erinacei, which produces its own antibiotics - an arms race running on a hedgehog's back.
• The oldest scientifically verified European hedgehog, a male called Thorvald from Denmark, reached 16 years - seven years beyond the previous record holder.
• Hedgehogs carry a protein called erinacin that blocks snake-venom haemorrhagins; a 2000 Toxicon paper showed it neutralises the main haemorrhagic metalloprotease of Bothrops jararaca venom. This is not immunity to snake venom. Erinacin is an antihaemorrhagic factor: it inhibits one class of venom enzyme - metalloproteases that rupture blood vessels - and does nothing against neurotoxins. It was purified from muscle extract and tested in the lab, not in bitten animals, and hedgehogs bitten by adders can still die.
• A hedgehog walks roughly one to two kilometres a night and rarely uses the same daytime nest for more than a few days, which is why sealed-off gardens are such a problem for them.
• The widely quoted figure of hedgehog hearing reaching 45 kHz comes from the long-eared hedgehog, not the familiar European garden species. Hearing in Erinaceus europaeus has barely been studied. The 45 kHz number belongs to a different species with conspicuously larger ears, yet it is routinely repeated as though it applied to the hedgehog in your garden.
• British colonists introduced hedgehogs to New Zealand in the 1870s out of homesickness; they are now classed as a pest that eats native invertebrates, small reptiles and ground-nesting birds' eggs.

“Hedgehogs are related to porcupines - or are some kind of spiky rodent.” Hedgehogs are not rodents and are not close to porcupines at all. Their nearest relatives are moonrats, gymnures, moles, desmans, shrews and solenodons. Porcupines are rodents; the resemblance is convergent evolution, not kinship.

“A cornered hedgehog can shoot, throw or fire its spines at an attacker.” Hedgehog spines are unbarbed and firmly anchored in the skin - they do not detach at all. A hedgehog's only defence is to roll into a ball and wait. (Porcupines cannot shoot their quills either; theirs merely detach on contact.)

“Put out a saucer of bread and milk for the hedgehog in your garden.” Hedgehogs are lactose intolerant. Milk causes diarrhoea, which can kill a small animal fast, and bread carries essentially no nutritional value for them. Meat-based cat or dog food plus a shallow dish of water is what the RSPCA actually recommends.

“Hedgehogs are crawling with fleas that will jump onto your cat or dog.” The flea found on hedgehogs is a specialist, Archaeopsylla erinacei, built for a spiny coat. It will not establish itself on a cat, dog or person. Most wild hedgehogs carry only a few resident fleas, which do them no harm.

“That spiky little animal in the pet shop - or the one in Madagascar documentaries - is a hedgehog.” Spiny tenrecs from Madagascar look almost identical to hedgehogs but sit in a completely different order, Afrosoricida, part of the African mammal radiation that also produced elephants and aardvarks. Another case of convergent evolution rather than family resemblance.

Sonic the Hedgehog launched on the Sega Mega Drive/Genesis on 23 June 1991 and, bundled with the console, moved around 15 million copies - the best-selling game on any Sega system. Paramount's live-action adaptation reached cinemas in February 2020 only after the first trailer's character design drew such fan backlash that director Jeff Fowler's team rebuilt Sonic and the studio pushed the release back from November 2019; sequels followed in April 2022 and December 2024. Hedgehogs were literary long before Sega. Lewis Carroll's Alice's Adventures in Wonderland (1865) stages the Queen's croquet match with live hedgehogs as balls and flamingos as mallets. Beatrix Potter's The Tale of Mrs. Tiggy-Winkle appeared in October 1905. Yuri Norstein's ten-minute Soyuzmultfilm short Hedgehog in the Fog (1975) was voted the greatest animated film ever made by the 140 animators polled at the 2003 Laputa Animation Festival. Muriel Barbery's novel The Elegance of the Hedgehog (2006) became an international bestseller. And Schopenhauer's 1851 parable - written about porcupines, not hedgehogs - survives as the "hedgehog's dilemma", the title of Neon Genesis Evangelion's fourth episode, broadcast 25 October 1995.

Thorvald is the only hedgehog holding a world record. A male living near Silkeborg in central Denmark, he was killed by a dog in 2016; volunteers in a Danish citizen-science project recovered his body, and researchers counting growth rings in a thin section of his jawbone found sixteen - announced in February 2023 as the oldest European hedgehog ever verified, seven years beyond the previous record holder. Beatrix Potter kept a real pet hedgehog named Mrs Tiggy-winkle, carried her along while travelling, and drew her as the model for The Tale of Mrs. Tiggy-Winkle, published in October 1905. In the internet era, Mr Pokee - an African pygmy hedgehog belonging to Talitha Girnus of Wiesbaden, Germany - passed a million Instagram followers before dying in March 2019 from a bacterial infection after dental surgery. A successor hedgehog, Herbee, inherited the account.