The hedgehog is a spiny mammal belonging to the subfamily Erinaceinae within the eulipotyphlan family Erinaceidae. This subfamily comprises 17 species across five genera, distributed across Europe, Asia, Africa, and, through introduction, New Zealand. While no hedgehogs are indigenous to Australia or currently exist natively in the Americas, the extinct genus Amphechinus formerly inhabited North America.
A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are 17 species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction. There are no hedgehogs native to Australia and no living species native to the Americas. However, the extinct genus Amphechinus was once present in North America.
Hedgehogs exhibit a distant phylogenetic relationship with shrews (family Soricidae), with gymnures potentially representing an evolutionary intermediate. Their morphology has remained largely consistent over the past 15 million years. Similar to many early mammalian forms, hedgehogs have evolved a nocturnal lifestyle. Their distinctive spiny defense mechanism bears a resemblance to that of porcupines, which are rodents, and echidnas, a type of monotreme.
In Europe, hedgehogs are frequently admitted to wildlife clinics. These animals are highly sensitive and susceptible to stress induced by human interaction, a condition that can prove lethal. Consequently, when hedgehogs are brought in for medical attention, veterinary facilities advise housing them in a dark, well-ventilated enclosure with minimal auditory disturbance, and strictly limiting direct handling or other forms of interaction.
Etymology
The term hedgehog emerged around 1450, originating from the Middle English heyghoge. This compound word is formed from heyg or hegge, meaning 'hedge', reflecting the animal's common presence in hedgerows, combined with hoge or hogge, meaning 'hog', due to its distinctive pig-like snout. Alternative appellations include urchin and hedgepig.
Description
Hedgehogs are readily identifiable by their characteristic spines, which consist of hollow hairs rigidified by keratin. These spines are neither venomous nor barbed and, in contrast to porcupine quills, do not readily detach from the animal's body. Nevertheless, juvenile hedgehogs undergo a process known as 'quilling,' during which their immature spines are shed and replaced by adult spines. Additionally, spines may be lost if the animal is afflicted by disease or subjected to severe stress. Typically, hedgehogs exhibit a brown coloration with pale-tipped spines, although blonde variants have been observed on the Channel Island of Alderney.
When confronted by a threat, hedgehogs typically curl into a compact, spiny sphere, thereby protecting their vulnerable face, feet, and abdomen. The dorsal region of the hedgehog possesses two substantial muscles responsible for controlling the quills. Certain lighter-weight desert hedgehog species, characterized by fewer spines, tend to either escape or engage in an attack, using their spines to ram an aggressor, resorting to rolling up only as a final defensive measure.
Hedgehogs are predominantly nocturnal, although diurnal activity has been observed in some species. During daylight hours, hedgehogs typically rest for extended periods beneath bushes, within grasses, under rocks, or, most frequently, in subterranean dens. All wild hedgehog species possess the capacity to hibernate; however, the duration of this dormancy is contingent upon ambient temperature, species-specific traits, and food availability.
Hedgehogs exhibit a notable vocal repertoire, encompassing a range of grunts, snuffles, and squeals.
Hedgehogs periodically engage in a ritualistic behavior termed anointing. Upon encountering a novel scent, the animal will lick and bite the source, subsequently generating a scented froth in its mouth, which it then applies to its spines using its tongue. Certain experts hypothesize that this behavior may function to camouflage the hedgehog by integrating it with local environmental scents, and could potentially transmit infection to predators impaled by the spines. Anointing is occasionally referred to as anting, drawing a parallel to a similar behavior observed in avian species.
Similar to opossums, mice, and moles, hedgehogs possess a degree of natural immunity to certain snake venoms, attributed to the presence of the protein erinacin in their musculature; however, the quantity is often insufficient to prevent a viper bite from being fatal. Furthermore, hedgehogs represent one of four mammalian taxa known to exhibit natural resistance to α-neurotoxin, another type of snake venom. Pigs, honey badgers, mongooses, and hedgehogs have independently evolved mutations in the nicotinic acetylcholine receptor, which effectively inhibits the binding of snake venom α-neurotoxin.
The olfactory capabilities of hedgehogs have received limited scientific investigation, primarily because the mammalian brain's olfactory region is concealed within the neopallium. Preliminary studies indicate that hedgehogs exhibit olfactory electrical activity patterns comparable to those observed in felines.
Diet
Despite their historical classification within the now-obsolete order Insectivora, hedgehogs are omnivorous. Their diet encompasses insects, snails, anurans (frogs and toads), snakes, avian eggs, carrion, fungi, grass roots, berries, and melons. Specifically, Afghan hedgehogs consume berries extensively in early spring following hibernation. Observations have also documented hedgehogs consuming cat food inadvertently left outdoors for domestic animals.
Hibernation
During hibernation, a hedgehog's core body temperature significantly drops from its typical range of 30–35 °C (86–95 °F) to a much lower 2–5 °C (36–41 °F).
Reproduction and Lifespan
The gestation period for hedgehogs varies by species, typically ranging from 35 to 58 days. Litter sizes average three to four offspring for larger species and five to six for smaller species. Infanticide, specifically the killing of newborn males by adult male hedgehogs, is a documented behavior, consistent with observations in numerous other animal species.
Hedgehogs exhibit a comparatively extended lifespan relative to their body size. In captive environments, where predation is absent and diets are regulated, individuals can live for eight to ten years, contingent on their size. Wild populations of larger species typically survive for four to seven years, with some documented cases reaching up to 16 years, while smaller species generally live for two to four years (or four to seven years in captivity). This longevity contrasts with that of a mouse, which lives approximately two years, and a large rat, which lives three to five years.
Neonatal hoglets are born blind, and their quills are initially encased within a protective membrane. This membrane desiccates and retracts over several hours, subsequently detaching following the mother's cleaning, thereby facilitating the emergence of the quills.
Predators
Diverse hedgehog species face a range of predators. Forest-dwelling hedgehogs are predominantly preyed upon by avian species, particularly owls, and by ferrets. Conversely, smaller species, such as the long-eared hedgehog, are vulnerable to predation by foxes, wolves, and mongooses. Osteological remains of hedgehogs have been identified within the regurgitated pellets of the Eurasian eagle owl, confirming their status as a prey item.
In Britain, the European badger constitutes a significant predator in regions characterized by intensive farming, correlating with reduced hedgehog populations in areas with high badger densities. Consequently, certain hedgehog rescue organizations refrain from reintroducing hedgehogs into documented badger territories. Furthermore, badgers engage in interspecific competition with hedgehogs for food resources.
Domestication
The predominant hedgehog species maintained as pets are hybrids derived from the white-bellied or four-toed hedgehog (Atelerix albiventris), occasionally referred to as the African pygmy hedgehog, and the diminutive North African hedgehog (A. algirus), also known as the pygmy hedgehog. Additional species commonly kept in captivity include the long-eared hedgehog (Hemiechinus auritus) and the Indian long-eared hedgehog (H. collaris).
As of 2019, the private ownership of hedgehogs as pets is prohibited in several U.S. jurisdictions, including the states of Hawaii, Georgia, Pennsylvania, and California, alongside New York City, Washington, D.C., and certain Canadian municipalities. The breeding of hedgehogs necessitates specific licensing. Conversely, most European nations, with the notable exception of Scandinavia, do not impose such restrictions. However, in Italy, the keeping of wild hedgehogs as pets is explicitly illegal.
As Invasive Species
In regions where hedgehogs have been introduced, such as New Zealand and the Scottish islands, they have established themselves as invasive pests due to the absence of natural predators. In New Zealand, this has led to the severe decline of indigenous species, encompassing insects, snails, lizards, and ground-nesting birds, with a particular impact on shorebirds.
Eradication efforts for invasive hedgehog populations often encounter significant challenges. Initiatives to remove hedgehogs from bird colonies on the Scottish islands of North Uist and Benbecula, located in the Outer Hebrides, provoked international opposition. The eradication program commenced in 2003, resulting in the culling of 690 hedgehogs, despite intervention attempts by animal welfare organizations to rescue them. By 2007, legal injunctions halted the culling, leading to a revised elimination strategy in 2008 that involved trapping and subsequent relocation to the mainland.
A 2022 report indicated a substantial and rapid decline in the hedgehog population across rural Britain, with estimates showing a reduction of 30–75% since the year 2000.
Diseases
Hedgehogs are susceptible to numerous diseases prevalent among mammals, such as various forms of cancer, fatty liver disease, and cardiovascular conditions.
Cancer is frequently observed in hedgehogs, with squamous cell carcinoma being the most prevalent type. This malignancy exhibits rapid metastasis from bone tissue to internal organs, a progression distinct from that typically observed in humans. Surgical intervention for the removal of bone tumors is generally not feasible.
Fatty liver disease and cardiac conditions are hypothesized to result from an imbalanced diet and obesity. Hedgehogs readily consume foods rich in fat and sugar, notwithstanding their metabolic adaptation for a diet primarily composed of low-fat, protein-dense insects.
Approximately ten percent of four-toed hedgehogs are affected by wobbly hedgehog syndrome.
Hedgehogs demonstrate high susceptibility to pneumonia, characterized by dyspnea and nasal discharge, which is caused by the bacterium Bordetella bronchiseptica.
Infrequently, hedgehogs can transmit a fungal dermatophytosis, commonly known as ringworm, to human handlers and other hedgehogs. This infection is caused by Trichophyton erinacei, which represents a distinct mating group within the Arthroderma benhamiae fungal complex.
Hedgehogs are susceptible to balloon syndrome, an uncommon ailment characterized by gas accumulation beneath the skin due to injury or infection, leading to the animal's inflation. This condition is distinctive to hedgehogs, attributed to their sufficiently loose skin that allows for curling. In 2017, the BBC documented a specific instance involving a male hedgehog that was "almost twice its natural size, literally blown up like a beach ball with incredibly taut skin." Bev Panto, a veterinarian at Stapeley's Wildlife Hospital, commented on the phenomenon, stating, "I have seen three or four of these cases and they are very strange every time and quite shocking ... When you first see them they appear to be very big hedgehogs but when you pick them up they feel so light because they are mostly air." The British Hedgehog Preservation Society offers guidance on this condition.
This condition lacks a singular etiology. Air can be expelled via incision or aspiration through the dorsal skin, and antibiotic prophylaxis is recommended. Potential contributing factors include lung or chest wall trauma, a minor external wound functioning as a valve, or a clostridium-type infection.
Anthropogenic Impact
Similar to numerous small mammals cohabiting with humans, hedgehogs frequently become road casualties while attempting to traverse thoroughfares. In Ireland, hedgehogs represent a prominent mammalian species among road fatalities. A study conducted between April 2008 and November 2010 documented 133 hedgehog deaths across two road segments spanning 227 km and 32.5 km. Analysis of an additional 135 hedgehog carcasses gathered across Ireland revealed a statistically higher proportion of male fatalities compared to females, with male mortality peaking in May and June. Conversely, female deaths surpassed male deaths exclusively in August, with additional peaks for females noted in June and July. These observed mortality peaks are hypothesized to correlate with the breeding season for adults and the dispersal or exploratory behaviors of juveniles post-independence.
Studies have indicated that hedgehog populations exhibit greater densities in urban settings when contrasted with rural landscapes.
Gastronomic and Therapeutic Applications
Hedgehogs serve as a dietary component in numerous cultures, having been consumed in Ancient Egypt and featured in certain Late Middle Ages culinary preparations. Across Eurasia and Africa, they are commercially exchanged for use in traditional medicine and sorcery. Particularly among Bedouin communities in the Middle East, hedgehog meat is regarded as a therapeutic agent for rheumatism and arthritis. Furthermore, hedgehogs are purportedly efficacious in treating a range of conditions, from tuberculosis to impotence. In Morocco, the inhalation of smoke derived from burnt hedgehog skin or bristles is believed to alleviate fever, impotence, and urinary ailments; the animal's blood is marketed as a remedy for ringworm, chapped skin, and warts, while its flesh is consumed to counteract witchcraft. Romani communities continue to consume hedgehogs, prepared either boiled or roasted, and also utilize their blood and fat for medicinal purposes.
In 1981, Philip Lewis, a British publican, introduced a range of "Hedgehog Flavoured Crisps," reportedly formulated to emulate the seasonings employed by Romani people in preparing baked hedgehogs. Given the absence of actual hedgehog ingredients, the Office of Fair Trading mandated a nomenclature alteration to "Hedgehog Flavour Crisps."
Genera and Species
Subfamily Erinaceinae (Hedgehogs)
- Genus Atelerix
- Four-toed Hedgehog, Atelerix albiventris
- North African Hedgehog, Atelerix algirus
- Southern African Hedgehog, Atelerix frontalis
- Somali Hedgehog, Atelerix sclateri
- Genus Erinaceus
- Amur Hedgehog, Erinaceus amurensis
- Southern White-breasted Hedgehog, Erinaceus concolor
- European Hedgehog, Erinaceus europaeus
- Northern White-breasted Hedgehog, Erinaceus roumanicus
- Genus Hemiechinus
- Long-eared Hedgehog, Hemiechinus auritus
- Indian Long-eared Hedgehog, Hemiechinus collaris
- Genus Mesechinus
- Daurian Hedgehog, Mesechinus dauuricus
- Hugh's Hedgehog, Mesechinus hughi
- Small-toothed Forest Hedgehog, Mesechinus miodon
- Gaoligong Forest Hedgehog, Mesechinus wangi
- Genus Paraechinus
- Desert Hedgehog, Paraechinus aethiopicus
- Brandt's Hedgehog, Paraechinus hypomelas
- Indian Hedgehog, Paraechinus micropus
- Bare-bellied Hedgehog, Paraechinus nudiventris
Societal and Cultural Significance
Across global folklore, hedgehogs are symbolically linked to intelligence and wisdom in Asian and European traditions, and to magic in African contexts.
Hedgehogs consistently rank as the most favored animal in British public opinion surveys.
References
- Hedgehog reference at the University of Michigan Museum of Zoology
- Hedgehog care and advice
- "Hedgehog" . In Encyclopedia Americana. 1920.
- "Hedgehog" . Encyclopedia Americana. 1920.Source: TORIma Academy Archive