The energetics of burrow excavation by the inland robust scorpion, Urodacus yaschenkoi (Birula, 1903)

Abstract

The inland robust scorpion, Urodacus yaschenkoi (Urodacinae, Scorpionidae), is a large (~3 g) semifossorial scorpion that is widespread in arid regions of Australia. It constructs spiralling burrows up to 1 m deep in sandy soils. This study determined the net cost of transport (NCOT) by burrowing, which represents the energy used in horizontally burrowing a given distance, excluding maintenance metabolism. A mathematical model generally applicable to semi-fossorial species was developed and used to estimate the total cost of burrow construction. The model incorporates (1) horizontal NCOT, (2) the cost of moving spoil and the animal’s mass along the length of the tunnel, and (3) the cost of working against gravity to raise spoil and the animal’s mass to the surface. The total cost of burrow excavation to a depth of 47 cm was estimated to be 350–530 J. This represents approximately 2% of an adult scorpion’s yearly energy turnover. Interspecific allometric comparisons of published NCOT data from phylogenetically diverse burrowers (with body masses spanning over two orders of magnitude) showed that burrowing method and substrate are important determinants of NCOT. Specifically, the cost of constructing an open tunnel through damp or dry sand is higher than the cost of moving through wet sand or mud without forming a tunnel.