Devil's Bolete
Rubroboletus satanas
Also called satan's bolete
A massive, pale-capped bolete of warm limestone woodland, with blood-red pores, a squat bulbous stipe covered in a fine red net, and flesh that blues only slowly.
Overview
The Devil's Bolete is among the bulkiest fungi of European woodland, with caps that can exceed 25 cm and a stipe so thick and swollen that young specimens look almost spherical. Its ghostly pale, chalk-grey cap over a sheet of blood-red pores gives it an unmistakable presence on the woodland floor.
Once placed in Boletus, it is now the type species of Rubroboletus, a genus assembled for the pale- to pink-capped, red-pored boletes with netted stipes and generally weak blue staining. Its dramatic common name is a piece of long-standing folk nomenclature and dates back to nineteenth-century mycology.
It is a thermophilic species, largely confined to the warmer, drier limestone districts of central and southern Europe, and in cooler northern regions it is a genuinely rare and localised find that many field mycologists never encounter.
How to identify it
Cap
Enormous when mature, commonly 10–25 cm and occasionally 30 cm across, hemispherical for a long time before flattening. The surface is dry, matt to slightly felty and often finely wrinkled or minutely cracked, coloured chalky white to pale grey, dirty cream or very pale buff, sometimes with faint olive or pinkish flushes towards the margin in age.
Pores
Small and round, yellow in the earliest buttons but quickly turning deep blood red to carmine over most of the surface, usually with a narrow yellow margin. Bruising turns them blue, though often more slowly and less intensely than in Neoboletus or Suillellus. The tube layer behind the pores is greenish-yellow.
Stipe
Very stout and squat, typically shorter than the cap is wide, strongly swollen to almost turnip-shaped and 4–10 cm thick. It is yellow at the apex, passing through carmine to blood red over the middle and belly, and paler again at the base. A fine, dense red network covers much of the surface, most obvious on the upper half.
Flesh and spore print
Thick and firm, whitish to pale lemon yellow, reddish in the extreme stipe base, changing to a modest pale blue on cutting and often fading back within minutes. Mature fruit bodies develop a strong, unpleasant sweetish-fetid odour. The spore print is olive-brown.
Where and when it grows
Rubroboletus satanas is a mycorrhizal partner of broadleaved trees, chiefly oak, beech, hornbeam, sweet chestnut and lime, and it is closely tied to calcareous soils over chalk and limestone. Typical sites are sunny, sheltered woodland edges, south-facing beech hangers, coppiced slopes and warm woodland rides where the ground heats up in summer.
Fruiting is concentrated in high summer and early autumn, often after thunderstorm rain following a hot spell. The species is widespread in central and southern Europe, reaching its northern limit in southern Britain and southern Scandinavia where it is rare and confined to the warmest limestone districts; related species occur in Asia and North America.
Ecological role
Like other members of the Boletaceae, this is an ectomycorrhizal fungus, sheathing the fine roots of its host and trading soil-derived nutrients for tree sugars. Its restriction to warm calcareous ground reflects both the physiology of the fungus and the distribution of the thermophilic oak and beech woodland it depends on, which makes it a useful indicator of long-established, unimproved limestone woodland.
Colonies are typically small and long-lived, producing only a handful of fruit bodies in favourable years and none at all in cool, wet summers. Because of this patchiness and its habitat specialisation, it is treated as a species of conservation interest in several northern European countries.
Similar species
Rubroboletus legaliae is the nearest relative in look: it has a distinctly pink-flushed cap rather than a chalky white one, a slimmer stipe and stronger blue staining. Rubroboletus rhodoxanthus also has pink to rose tones on the cap and a bright yellow, only partially reddened stipe, and its cap flesh blues while the stipe flesh stays yellow.
The Lurid Bolete (Suillellus luridus) is browner and more olive-capped with a slimmer, less bulbous stipe, and its flesh turns blue instantly. Pale-capped members of Butyriboletus, such as Butyriboletus appendiculatus, share the netted stipe but have yellow pores throughout rather than red ones.