Useful or no, that thing gives me the Zagaxy horripilations!

Speyeder

Frequency: Extremely rare.
No. appearing : 1-4
Armor class : 6
Move : 6"
Hit dice : 1
% in lair : 70%
Treasure type :
No. of attacks : 1
Dmg/attack : 1-4
Special attacks :  poison
Special defenses : never surprised
Magic resistance : 40%
Intelligence : Low
Alignment : Neutral Evil
Size : S, 1 to 2 hand spans in width
Psionic ability : nil

The Speyeders appear to be arcane constructs, or else, natural creatures magically altered, which have escaped into the wider world and there found a degree of success sufficient to allow them to maintain a small but stable population. Speyeders are similar to spiders of the orb-weaving sort, save for the fact that their abdomen seems to be a large, moist and naked human eyeball.

Left to their own devices, speyeders act as would any large arachnid possessing a dim and malign intelligence.  They prey upon small rodents, birds, large insects, and unfortunate pixies.  In most cases, speyeder venom is but weakly poisonous. Creatures possessing more than 1 hit die which are bitten by a speyeder may save vs. poison and take only 1d8 damage if successful.

Magical creatures are of course, highly variable. Instances of speyeder venom causing

 hallucinations, alignment changes or spontaneous outbursts of poetry have been reported.

A rare and dangerous variant is the Mesmeric Speyeder.  From the center of their black spiral webs, these speyeders may charm into immobility any creature which unexpectedly meets the gaze of their abdominal eye.  Victims will be fed upon by the speyeder until death.  This may take weeks, as only 1d4 points of damage per day is caused by the fluid loss.

A spell exists, originator unknown, most often referred to as Speyeder Sight, which allows the caster to see through a speyeder’s abdominal eye, and also to direct its movements for a time. This turns a speyeder into an excellent spy, which may be the entire reason for the creatures existence. Because the spell is so rarely found, the full extent of its design is uncertain. Partial examples have resulted in unfortunate side effects.

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Found a picture on the intertubes, made a monster for it.