‘174 THE AUSTRALIAN NATURALIST. 
NESTS OF THE MOUND ANT, IRIDOMYRMEX 
DETECTUS. 
By Tos. STEEL. 
This ant, known also as the Road Ant, is common all over 
Australia. Its nests are familiar objects by the roadsides and in 
open places everywhere, being always free from vegetation and 
covered with a layer of small stones or pebbles mixed with frag- 
ments of twigs. It is generally supposed that the pebbles are 
merely what have been met with in the process of excavating 
the nest, and that they are ‘leposited on the surface merely to 
get rid of them. For a long time past it has appeared to me 
that the quantity of pebbles on a nest was out of all propor- 
tion to the extent of the excavations beneath the surface, and it 
seemed impossible that they could all have been obtained in this 
way. Observation has shown me that the pebbles are collected 
in the vicinity of the nest and breught and deposited thereon 
by the ants. 
T noticed a nest near a footpath at Pennant Hills, which was 
covered with the usual small brown pebbles of the district, de- 
rived from the weathering of the Hawkesbury shale. It chanced 
that the footpath was repaired with engine ashes, and in a very 
few days quantities of small fragments of cinders were collected 
and placed on the nest by the ants. Another nest at the edge 
of the Pennant Hills railway station and close to a macadamised 
roadway, no shale pebbles being near, is covered with a mixture 
of small granite pebbles from the station platform, and frag- 
ments of dolerite derived from the roadway. 
Usually when such are available, fragments of twigs are seat- 
tered amongst the pebbles, the latter always consisting of what 
is available in the immediate vicinity of the nest. A nest which 
I examined in Kuringai Chase was covered with a mixture of 
small quartz pebbles from the disintegration of the sandstone 
and fragments of charcoal from a fireplace near by. Hxamples 
from above-mentioned nests are exhibited. I feel puzzled to ac- 
count for this habit of the ants. On referring the matter to Mr. 
Froggatt, he suggested that possibly it was to act as a cover to 
keep the nest cool in summer; but this does not seem very con- 
vincing to me. Perhaps some of our members may be able to 
elucidate the matter. 
As these ants are often a nuisance, constructing their nests 
on garden footpaths and similar situations J have tried many 
