HISTOKY AND DISTRIBUTION. 17 
by the variation in the amount of precipitation annually as between 
different localities, for they seem to flourish as well at San Jose and 
Los Angeles, Cal., with average annual rainfalls of 14.8 and 15.6 
inches, respectively, as they do at New Orleans, La., where the aver- 
age annual rainfall is 57.6 inches. The range of temperature to 
which they have adapted themselves at different points does not 
vary so greatly, but is nevertheless considerable. They have suc- 
ceeded in establishing themselves at San Francisco, Cal., where the 
mean annual surface temperature is 56° F., or 13° cooler than the 
mean annual surface temperature at New Orleans, La. 
If we assume that the Argentine ant is unable to persist in local- 
ities where the mean annual temperature is below 55°, we will find 
that the isotherm of this temperature extends almost up to Columbus, 
Ohio, and past St. Louis, Mo., and will include over one- third of the 
United States, or more than 1,000,000 square miles. It is very 
unlikely, however, that this neotropical species will be able to endure 
the cold winters in the northern parts of this area. It will probably 
be more nearly correct to assume that its advance will be checked 
when it reaches the minimum isotherm of zero, or, in other words, 
where the thermometer drops to zero or below during the average 
winter. On constructing this isotherm we find that we have the 
following area within the United States liable in the course of time 
to infestation by the Argentine ant : 
Starting at the Atlantic coast line; one-half of North Carolina, 
one-half of South Carolina, one-half of Georgia, Florida, a portion of 
Alabama, one-third of Mississippi, most of Louisiana, all of lower 
Texas, a corner of New Mexico, one-half of Arizona, a little of Ne- 
vada, practically all of California, and a coastal strip through Oregon 
and Washington. This would extend the infestation into fourteen 
States, more or less, and is undoubtedly a very conservative predic- 
tion, as already the ant is established at one point, Delta, La., which 
is above this line. 
In spite of these considerations we are still in the dark as to the 
altitudes at which this insect will thrive, and it may be found later 
that altitude will severely limit the distribution of this species, as it 
does that of many other insects. Table I gives the elevation and 
climatological data for a number of infested points in the United 
States, and from this table it will be noted that the elevation of 
points now infested varies from sea level to 338 feet. 
The climatological data given in Table I are taken from Bulletin Q, 
Weather Bureau of the United States Department of Agriculture, 
1906, entitled "Climatology of the United States," by Alfred Judson 
Henry. 
75508°— Bull. 122—13 2 
