KingdomFungiGenusRubroboletusSpeciessatanas
Rubroboletus satanas
T1 · Gastrointestinal irritantPublished 2026-10-22Late summer / Autumn
Satan's bolete has one of the most alarming names in mycology and a syndrome that is serious but almost never fatal, which is itself worth knowing: the reputation comes from the colour scheme, not from the mortality. What matters practically is that it is the one bolete in temperate Europe that reliably turns a forager's cut test into a hard stop.
Block 01 · Record
Red pores and blueing flesh
The pore surface is blood-red from the moment the fruit body pushes out of the soil and never passes through a white phase — which is the opposite of Boletus edulis, whose pores are white and only yellow with age. Cut the flesh and it blues within ten seconds, weakly in the cap and dramatically in the stem base. Those two characters together exclude every edible bolete in the region, and neither requires microscopy or a reagent. If a bolete has red pores and blues when cut, it does not go in the basket, whatever else it looks like.
Spores and the reagent bench
The spore print is olive-brown and needs a night on white paper. Spores are 10-14 x 5-6.5 micrometres, subfusiform to ellipsoid, smooth and inamyloid — shorter and relatively broader than Boletus edulis spores. On the bench the species reacts to everything: potassium hydroxide turns the cap orange-brown, iron(II) sulfate gives a grey-green to olive wash on the flesh within thirty seconds, and ammonia turns both flesh and pore surface greenish-blue immediately. None of those reactions is diagnostic on its own; all three together fit this species and not B. edulis.
Chalk soils, oak and a southern distribution
Rubroboletus satanas is ectomycorrhizal on calcareous and neutral soils, most often with oak and sweet chestnut and occasionally with beech and hornbeam. It is a southern and western European species and it is associated with warm, dry, base-rich woodland edges and open stands; in Britain it is largely confined to the south, and it becomes commoner moving south and east across the continent. Fruit bodies appear from late July to October, are often half-buried because of the massive base, and can be very large — caps of 250 mm are recorded.
The syndrome and the reputation
The species produces a severe gastrointestinal syndrome — violent vomiting, diarrhoea and abdominal pain with a latency of thirty minutes to three hours — and the older literature described it as deadly. Modern poison centre data do not support that: cases are serious, dehydration is common, hospital admission happens, but deaths are rare and are usually in frail patients. The tier is T1 because the syndrome is self-limiting and no organ toxin has been characterised — but T1 is a statement about the category of harm, not about how bad the afternoon will be.
Points to carry to the bench
- Blood-red pore surface from the earliest stage, never white at any age.
- Flesh blues within ten seconds of cutting, strongly at the stem base.
- Spores 10-14 micrometres, smooth, inamyloid; spore print olive-brown.
- Calcareous soil with oak, southern European distribution; T1 severe but self-limiting gastrointestinal syndrome.
| Cap | shape: Hemispherical then convex to plano-convex, 80-250 mm across, very thick-fleshed; the margin is inrolled for a long time and remains thick and entire.surface: Dry, finely tomentose to almost smooth, pallid grey-white to ochre-grey, sometimes with a faint pinkish tinge at the margin.margin: Thick, inrolled, entire; no sterile band of a contrasting colour as in Boletus edulis. |
|---|---|
| Gills | attachment: Tubes rather than gills: 5-15 mm deep, adnate to depressed around the stem apex, with a yellow tube layer at the stem and blood-red pores at the surface.spacing: Pores small and round, 0.3-1.0 mm across, 2-4 per millimetre, red from the earliest stage and never passing through a white phase.edge: Pore edges thin and entire; pressure or injury may turn them blue-green but they never become yellow. |
| Spore print | Subfusiform to ellipsoid, smooth, with a suprahilar depression and a short hilar appendix.Smooth and inamyloid; the spores are shorter and relatively broader than those of Boletus edulis. |
| Habitat and season | Ectomycorrhizal on calcareous and neutral soils, most often with oak and sweet chestnut, sometimes with beech and hornbeam; a southern and western European species associated with warm, dry, base-rich woodland edges and open stands. |
Block 02 · Chemistry
| Reagent | Verdict | Reaction | Weight |
|---|---|---|---|
 MELZ | inamyloid | Spore wall stays olive; no blue-black or rusty development. | 3.00 |
 KOH5 | positive | Cap cuticle turns orange-brown; the red pore surface darkens to a deeper blood-red without turning yellow. | 2.00 |
 FESO4 | positive | Flesh develops a grey-green to olive wash within 30 s, faster and stronger in the stem base than in the cap. | 3.00 |
 NH4OH | positive | Flesh and pore surface turn greenish-blue immediately, especially at the stem base. | 2.00 |
Injury stain Flesh blues within ten seconds of cutting, weakly and slowly in the cap and strongly and rapidly in the stem base; the pore surface also blues on pressure. This is the character that separates it from Boletus edulis in a single cut, and it is the reason the two are never confused at the bench even when they are confused in a photograph.
Block 03 · Confusion
| Separating character | This record | Confused with |
|---|---|---|
| Pore surface white to olive at every age and never red, a fine white reticulum on the stem, and no blueing at the cut. One cut settles it in ten seconds. | Rubroboletus satanasT1 | Boletus edulis▲ +1 |
| An orange-red pore surface, a red reticulum on the stem, and a yellow-brown cap; it is also a gastrointestinal irritant and is separated from R. satanas by the orange rather than blood-red pores. | Rubroboletus satanasT1 | Suillellus luridus▲ +0 |
| A pinkish-flushed cap with a red reticulum confined to the upper stem, and the same blueing flesh; treated as the same hazard, separated on the extent of the reticulum. | Rubroboletus satanasT1 | Rubroboletus legaliae▲ +0 |
Toxicity ladder
Reproducible vomiting, cramping and diarrhoea with no hepatic, renal or neurological involvement. Onset is short and recovery is complete, but the same species can produce a severe dehydrating episode in children and in people on diuretics or beta blockers.
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