94 THE ARGENTINE ANT. 
seems not to be lessened thereby. During flood time many of the au.t 
colonies migrate to the levee adjoining, while still others ascend the* 
trees out of the water's way. Curious nests or sheds, constructed 
by the ants from particles of earth and trash, are of common occur- 
rence in the tops of the willow trees. 
In some few places it is evident that the railroad has been the means 
of introduction, the infestation having started at points on the railroad 
where considerable merchandise from New Orleans was constantly 
being unloaded. 
EXPERIMENTS IN THE ORANGE GROVES. 
The writers' first experiments with the pest in orange groves were 
commenced in the spring of 1910. At that time only one grower in 
the Louisiana orange section was attempting anything like a system- 
atic campaign against the ants. This grower had adopted a novel 
and rather effective method of destroying them. The infested por- 
tion of his orchard immediately adjoined the levee and, as is usual 
with land along the river, was lower by several feet than the water in 
the river during flood stages. The water could therefore be siphoned 
over the levee to the orchard as rapidly as needed. (See PL X.) To 
prevent the spread of the ants to additional territory the infested 
block had been surrounded by a ditch, a section of which may also be 
seen in Plate X, in which water was kept at all times. During flood 
stages of the river the water was siphoned over for the ditches at small 
expense and through the ditch system drained away to the swamp in 
the rear of the plantation. At other times the water was kept in the 
"ant ditches" by use of a gasoline engine and pump installed on the 
levee, as shown in Plate X. It was, of course, necessary to take pre- 
cautions that the ants should not find accidental and artificial means 
of crossing the ditches. Permanent bridges for the passage of teams 
could not be left, so a swinging bridge which could be lifted when not 
in use was devised. The ditching system for preventing spread of the 
ants was shortly adopted by many other growers, some of whom used 
an ingenious divided bridge (PL XI) which could be crossed readily 
by teams, but which had a 2-inch crack through the middle that effec- 
tually prevented the. pass age of the ants. 
The grower referred to had put in practice the following method of 
destroying the ants: A small levee or ridge was made around the 
infested block of trees. Water was then admitted through the siphon 
from the river until the ground in the block was entirely covered. As 
the water slowly rose the colonies of ants moved up into the orange 
trees. Then the water was drawn off and the ants, descending, found 
the ground still too wet to live in, whereupon they migrated en masse 
to the surrounding small levee. The water was then turned on for 
the second time to keep the ants on this ridge, and here they were 
