Fossil wood is so drab that few paleontologists bother to examine it closely. However, a non-descript chunk of wood from the West Coast includes something quite special -- cryptic evidence of the most ancient social behavior.

Collishaw Point on Hornby Island in the Strait of Georgia is a favourite haunt of fossil collectors who come to search for the attractive Upper Cretaceous ammonites that occur in concretions at this site. A 10 cm diameter chunk of fossil driftwood includes cryptic fossils of some importance. A polished section of this wood reveals that it is riddled by unfilled holes about a centimetre across -- borings in the form of interconnected tunnels. Many of these holes are packed with six-sided millimetre-sized black pellets. These holes are galleries excavated by wood-boring insects and the black pellets could only be their fecal material -- frass to entomologists -- excrement backfilled into vacant galleries.

Many insects bore into wood -- beetles, termites, bees, ants, weevils, wasps and moths; but the order Isoptera (termites) is the only group that excavates galleries to make nests in the centre of wood. Termites are rare as fossils and termite nests in wood are almost unknown as fossils. The fossil log discovered on Hornby Island contains the oldest termite nest anywhere on earth -- well dated as 70 million years old.

Termites are considered a menace now because they eat wood. Cellulose, however, cannot be digested directly by termites. Recent wood-eating termites live in close symbiosis with protozoans which break down the cellulose into digestible carbohydrates in a fermentation chamber in the termite's gut. The Hornby nest and the fossil frass now provide strong circumstantial evidence that this termite-protozoan symbiosis dates, at least, from the Late Cretaceous.

Every living species of termite comprises separate castes -- queens, winged sexual forms, sterile workers and sterile soldiers -- each performing specific tasks in constructing and maintaining the nest and in ensuring the viability of the colony. So, although the Hornby fossils yield no direct evidence of the presence of different castes of termites in the Late Cretaceous, they must have existed then because a termite nest could only be built and maintained by the coordinated activity of different castes of one species -- diminutive evidence of perhaps the most ancient social behaviour discovered to date.

The termites that excavated the nest in that undistinguished log from Hornby Island shared their Cretaceous world with ammonites, dinosaurs, elasmosaurs, mosasaurs, ichthyosaurs and pterosaurs. These and many other animal groups perished in a cataclysmic mass extinction 65 million years ago. The termites, unperturbed in their sealed nests, carried on.