HISTORY AND DISTRIBTJTION. 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 Now 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 mclude over one-third of the 

 LTnited States, or more than 1,000,000- square miles. It is very 

 unlikely, however, that this neotropical species wall 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 reach-es the minimum isotherm of zero, or, in other words, 

 where the thermometer drops to zero or below during the av^erage 

 winter. On constructing this isotherm we find that we have the 

 following area within the United States liable m 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 tliis 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 



