These large elementals bore a resemblance to spiders and appeared to be composed entirely of magma and flame. Transparent plates on their bodies revealed a swirling mass of molten rock that formed their internal structure, while flames danced across the bulk of their abdomen and legs in random patterns. They had eight blazing eyes that were generally devoid of any expression.
On average inferno spiders stood approximately 4 feet (1.2 meters) tall, had a diameter of 8 feet (2.4 meters), and could weigh as much as 600 lb (270 kg).
These elementals possessed only a limited intelligence, yet were still very cunning and tenacious hunters. They were intelligent enough to realize the benefits of allying with stronger creatures and could follow simple orders.
These elementals had poisonous fangs, dripping in a sort of caustic liquid flame that burned victims from within. They could produce webs composed of a fiery substance. This substance kept them burning near indefinitely, but was vulnerable to cold-based attacks.
An inferno spider always began to engage their prey by attempting to entangle them in one of their webs. This allowed them to capture creatures that were otherwise too nimble or quick.
Inferno spiders lived largely solitary lives and avoided contact with others of their own kind.
Once in their life time, typically when one had become advanced in both size and years, an inferno spider would seek out a mate. Courting inferno spiders engaged a strange, ritualistic dance, during which they would circle each other for hours or, in some cases, even days. At the end of this ritual the two would charge one another, colliding and exploding into hundreds of newborn inferno spiders.
Very few of the resulting young would survive long. Partly because the enemies and predators of these elementals often hid near dancing mates, lying in wait to slay as many of their resulting offspring as possible. And partly because these young would attack their own siblings.
These elementals were voracious predators that hunted creatures weaker than themselves.
Weaker denizens of the Elemental Plane of Fire universally loathed these elementals. They were often in the company of clerics of fire deities, fire elementals, or groups of cunning salamanders. They were particularly attracted to individuals that possessed great arcane or divine power.
The vast majority of inferno spiders were servants of the deity Kossuth, whom they revered. To them he appeared as an enormous inferno spider of great age and strength. One of his faction of worshipers, the Burning Braziers, sought to introduce them to Toril as part of their quest to cleanse the world. However, for unknown reasons the deity only allowed them limited summoning of these elementals.
Following Halaster Blackcloak's death in 1375 DR, an inferno spider and a trio of magma hurlers crossed over into the Prime Material plane through a portal that opened in the Belkram's Fall area of Undermountain and proceeded to make their lair there.
On Ches 29, in the Year of Blue Fire, 1385 DR, a vampire in service of Szass Tam named Tammith Iltazyarra infiltrated the ziggurat of Kossuth in Escalant. As she progressed through it Tammith was assailed by an inferno spider, which after a short battle she managed to slay.
Sorcerers, wizards, and clerics with access to the fire domain could summon inferno spiders through use of summon monster IV or a high level summon monster spell. Alternatively, such clerics could call them to their aid through use of planar ally. Accomplishing any of these required completion of a magical ritual that involved the power of fire opals worth 100 gold pieces.
- Gwendolyn F.M. Kestrel (July 2006). Monster Manual IV. (Wizards of the Coast), p. 76. ISBN 0-7869-3920-6.
- Gwendolyn F.M. Kestrel (July 2006). Monster Manual IV. (Wizards of the Coast), p. 77. ISBN 0-7869-3920-6.
- Eric L. Boyd, Ed Greenwood, Christopher Lindsay, Sean K. Reynolds (June 2007). Expedition to Undermountain. Edited by Bill Slavicsek. (Wizards of the Coast), p. 112. ISBN 978-0-7869-4157-5.
- Brian R. James, Ed Greenwood (September 2007). The Grand History of the Realms. Edited by Kim Mohan, Penny Williams. (Wizards of the Coast), p. 158. ISBN 978-0-7869-4731-7.
- Eric L. Boyd, Ed Greenwood, Christopher Lindsay, Sean K. Reynolds (June 2007). Expedition to Undermountain. Edited by Bill Slavicsek. (Wizards of the Coast), p. 145. ISBN 978-0-7869-4157-5.
- Richard Lee Byers (March 2008). Undead. (Wizards of the Coast), pp. 29–36. ISBN 978-0-7869-4783-6.
Magical spiders: Bloodsilk • Electric • Glass • Gaze • Goblin • Pet of Kalistes • Spellgaunt • Steeder
Planar spiders: Demonweb terror • Fire • Myrlochar • Phase • Shadow • Tomb • Vortex
Constructs: Arachnar • Bone spider • Jade spider • Retriever • Spiderwalker • Stone spider
Outsiders: Bebilith • Darkweaver • Greelox • Inferno spider • Red widow • Yochlol
Creations of Lolth: Abyssal widow • Chwidencha • Drider (Vampire) • Shunned
Humanoids: Aranea • Chitine • Choldrith • Ettercap • Werespider
Miscellaneous: Kitthix • Neogi • Rhylfang • Susurrus
Undead spiders: Wraith spider