THE NEW MEXICO RANGE CATERPILLAR. 77 



The larvae seem to understand perfectly the value of the spines as 

 a means of defense, for when they are grasped in the fingers they at 

 once begin to twist their bodies with all their muscular force rolling 

 themselves upon the fingers and hand to drive the spines into the 

 flesh. 



The larvae often use these weapons upon each other, striking 

 viciously at times when two large caterpillars come into unexpected 

 and unwelcome contact. The results are not serious, but the efforts 

 to wound appear to be in real earnest. 



ABUNDANCE OF LARVAE. 



At different times during the summer, and at widely separate 

 points, as far distant as 30 miles, counts were made of the caterpillars 

 present on a measured square rod, in order to obtain some idea of 

 the numbers of the pests. In each case the area was carefully meas- 

 ured and marked, and all the larvae within the lines counted as they 

 were gathered, so that the figures given are in every instance secured 

 by an actual census. Efforts to estimate the numbers uniformly 

 resulted in a guess much below the actual facts. 



In a range pasture, many square miles in extent, near Koehler, N. 

 Mex., a count made August 17, 1909, showed 181 nearly full-grown, 

 active caterpillars feeding within the limits of a single square rod. 

 This means the enormous total of 18,534,400 upon one square mile. 

 While the numbers of the pests varied exceedingly, it is well within 

 the truth to assert that many square miles in the neighborhood of 

 Koehler were as densely infested as the square rod which was counted. 



In the vicinity of Clayton, N. Mex., a town situated on the im- 

 mense plains that extend far to the eastward across the Texas pan- 

 handle, the larvae of the Hemileuca attracted so little attention that 

 cattlemen who had observed them in former years declared over 

 their signatures that none was present in 1909. Almost within a 

 stone's throw of the residence portion of Clayton, on August 21, 1909, 

 as many as 10 and 15 were counted to the square rod, or a million to 

 a million and a half to the square mile. 



It might be noted in passing that the failure to observe the exist- 

 ence of these caterpillars when present in only moderate abundance 

 is not wholly due to lack of trained powers of observation, for the 

 colors of soil and vegetation afford a certain amount of protection 

 against discovery. 



July 2, 1909, on two adjacent clumps of bunch grass (Sporobolus 

 airoides) on the C. S. ranch, 17 miles from Springer, the caterpillars 

 seemed numerous and were counted. On one clump 117 were feed- 

 ing, on the other 128. These clumps were 20 to 24 inches across and 

 stood 3 feet apart. Three instars were represented on this grass. 



