218 COI.ORATION IN I.EPTINOTARSA. 



small amounts if the pressure is slight, and in greater amounts as the pressure 

 is increased. This liquid is volatile, and to the human senses has an unpleas- 

 ant odor and a rather unpleasant taste, and I see no reason why it might not 

 be equally disagreeable to insectivorous animals. At any rate, the glands as a 

 protective device have a high degree of efficiency, and although some of the 

 insects are eaten, the great majority are well protected thereby. I have ob- 

 served that young fowls, when turned loose in a potato field where the beetles 

 are common, attack them at first eagerly, but learn in three or four days that, 

 although they are easily found and tempting, they are not choice morsels as 

 food. Hence, after a few days, they are recognized by their striking yellow 

 and black surface and are avoided thenceforth, and to all intents and pur- 

 poses they are immune from that particular generation of fowls. 



I have also tried the experiment of mixing decemiineata with edible insects 

 in about equal quantities and feeding them to fowls, with the result that the 

 experienced fowls unerringly selected the edible and rejected the distasteful 

 insects, whereas the inexperienced fowls did not so certainly select the agree- 

 able from the nauseous. The different elements in the mixture were at first 

 taken in about the proportion of edible 65 per cent and inedible 35 per cent, 

 which would indicate that even although the new food had not been pre- 

 viously encountered and its distastefulness experienced, the mere fact that its 

 coloration was novel and different from the usual run of food caused it to be 

 investigated with some care before being consumed in quantities. At any 

 rate, the fowls soon learned to recognize and avoid this insect on account of 

 its conspicuous coloration. This fact was proven by an experiment in which 

 beetles whose yellow areas had been painted with blackened shellac were fed 

 to experienced fowls. The insects were eagerly seized at first, but as soon 

 as their distasteful qualities were discerned they were rejected. 



It can not be doubted that decemiineata, on account of its striking color- 

 ation and its accompanying inedible qualities, enjoys a high degree of im- 

 munity from its vertebrate enemies, and not because there is any instinctive 

 avoidance of the beetle by fov/ls and birds, but because each succeeding gen- 

 eration very soon becomes acquainted with its distasteful qualities and learns 

 to associate it with the sharply contrasted colors of its color pattern. In this 

 process of educating its public enemies decemiineata yearly sacrifices a small 

 percentage of its numbers, probably less than half of i per cent, but this sacri- 

 fice gives to the remaining 99 per cent far greater imaTiunity from enemies 

 than could otherwise be obtained. 



L. multitceniata and oblongata, which possess this same coloration and the 

 glands, are also, as far as I can discover, practically immune from the attacks 

 of insectivorous enemies. In fact, every species in the genus Leptinotarsa 

 possesses these glands to a greater or less degree, and almost all are marked 

 with bright colors in most striking contrast to one another and to their sur- 

 roundings, which render them as conspicuous as possible. Moreover, as far 



