PRELIMINARY REPORT ON THE BURROWS AND BEHAVIOR OF THE BARDI GRUB (INSECTA: LEPIDOTERA: HEPIALIDAE) FROM POINTBAR AND LEVEE DEPOSITS OF THE DARLING RIVER, BINDARA STATION, NEAR POONCARIE, NEW SOUTH WALES, AUSTRALIA

Vertical, silk-lined burrows of the Bardi grub (Lepidotera: Hepialidae) were accidentally discovered while studying the sedimentology and neoichnology of the Darling River on Bindara Station near Pooncaire, New South Wales, Australia. These burrows are of interest because they have a variety of morphologies that can be mistaken for: 1) the vertical burrow Skolithos; 2) the pellet-lined burrow Ophiomorpha; and 3) hollow, organic-walled rhizoliths. Two of us (STH, MR) have observed trace fossils in lower–middle Mesozoic coastal plain to shallow marine deposits in core with similar morphologies to that seen in Bardi grub burrows. The burrows in core have been interpreted by others as Ophiomorpha for a lack of a better representative ichnotaxon and have been interpreted as marine crustaceans burrows; hence, those units have been interpreted as shallow marine. Studying bardi grub burrows will aid in providing details of how similar continental burrows differ from such marine burrows as Ophiomorpha. Bardi grub burrows studied ranged from 35–50 cm long and 1.5–2.0 cm in diameter, and were found in compacted fine-grained sand composed entirely of climbing ripple stratification. From top to nearly the bottom, the burrow wall is lined (0.5–2 mm thick) with silk darkened to a blackish brown by flattened fecal pellets, composed of root and other plant material fed on by the grub, pressed or woven into the burrow wall. Several short backfilled meniscate tunnels radiate outward 4–10 cm from the burrow base that are roughly the same diameter or smaller than that of the burrow. Some of the menisci are composed of plant material that likely passed through the gut of the grub. The meniscae tips, however, point toward the main tunnel and indicate that the grub produced them as it burrowed back to the main burrow. This pattern suggests that the grub first burrowed outward and then turned around and burrowed back through the material it had previously excavated and packed to create the meniscae back to the main burrow. Burrowing experiments in the field demonstrate that the grub does line its burrow with silk, but it uses peristaltic motion to force itself into loose and slightly compacted sand. The grub could not penetrate the firm pointbar surface, however. We thank the landowners of Bindara Station for permission to camp and access to the Darling River.