The Hexcriveners, better known as Mentor Bugs, live on Suphis II, a planet in a solar system marooned inside a bethorm or pocket universe. Mentor Bugs are arborial insectile scriveners that range from 3-10 cm in length. Mentor Bugs can be found covering the bark of the Axis Mundi trees that ring the planet's equatorial continent.
Hexcrivener bugs live their brief lives in the summer month of Thermidor. (In the remainder of the year, they exist first as eggs embedded in the trees' bark, and later as soft grubs feeding on the leaves of the Axis Mundi trees.) In the month of Thermidor, mature Mentor Bugs descend from the branches of the Axis Mundi tree to attach to the bark of the trees' trunk. They consume the quantum liquor of the trees using their long, diamond tipped proboscis, and intoxicated by that liquor, begin to etch a variety of spells and psychic sutras into the bark of the tree on which they reside. During Thermidor, the trees glow at night with the numinous runes etched by Hexcriveners. Seen from orbit, the equatorial continent's nightside becomes one shimmering band of light.
Reading trees is one way for sorcerers, shamans, and priests to learn new spells and psychic sutras, as well as unusual variants of common spells. Care must be taken in the interpretation of these etchings, as the bark of any given tree will be a palimpsest consisting of several layers of etchings by one or more Mentor Bugs. Approaching the trees while the bugs are active is also quite dangerous - while the bugs are alive and etching, the spells are alive, and may be triggered by someone's approach.
The best courses of action for learning spells directly from the Mentor Bugs is to observe active etchings from a distance, using a spy glass. Scrying and clairvoyance spells may be dangerous for this purpose, triggering the discharge of bark-etched spells. So use non-magical means of observation. The etchings will reveal the nature of the spell. Hexscriveners use one or more of the magical languages commonly used to inscribe spells on scrolls. Finally, prayers and offerings to the Bug Gods are often used to try to influence which spells the Hexcriveners will inscribe next.
Once the month of Thermidor ends, the Hexcriveners lay their eggs in the bark and remain on the trees as lifeless husks. At this point, members of the Peelers Guild will strip the bark from many Axis Mundi trees and use the bark to fashion spell scrolls and scroll books. The Guild is quite protective of its harvest rights so it is best to avoid the areas where they are stripping the bark of the Axis Mundi trees.
Many brave the dangerous, remote wild areas of Suphis II's equatorial continent to harvest bark spell etchings unmolested by the Guild. Such travelers are often followed and harassed by Guild members when they return to more civilized lands. It is often best to memorize and transcribe spells acquired from the Axis Mundi trees, recording them in a proper spellbook before returning to civilized lands. The bark can then be burned; the ash of the Axis Mundi tree is useful as a spell component.