PITCHERPLANTS AND THEIR INSECT ASSOCIATES 



BY FRANK MORTON JONES 



Wilmington, Delaware 



VICTIMS OF THE PLANTS 



That the pitcherplants are "intended" as insect traps — that their capture of insects is not 

 an accident of evolution and of no real significance to the plants — is attested by a mass of 

 evidence v^hich in its entirety is overwhelming. Some of that evidence Will be presented here. 



The pitchered leaves, so flowerlike in coloration and shape that the nonbotanical observer 

 usually mistakes them for true flowers and often compares them with jack-in-the-pulpit or 

 with the spathes of the skunkcabbage, bear out an interpretation that their function, like 

 that of flowers, is the attraction of insects. Confirming that interpretation, these flowerlike 

 pitchers at their more active period diffuse a fruity or honeylike fragrance from a nectar 

 secretion containing fruit sugar, whose attraction for insects is often visibly evidenced by 

 columns of ants climbing their walls and feeding in rows upon the exuding nectar, or by wasps, 

 bees, butterflies, and moths flying from pitcher to pitcher, alighting and feeding upon the 

 nectar globules that stud their tops. The nectar glands are so distributed that they form 

 attractive pathways for the visiting insects, which are further guided by bristly hairs or by 

 a fine pile, so directed that a feeding insect is unconsciously urged toward and into the pitcher's 

 mouth. Within the mouth of the pitcher the surface texture changes to one of extreme 

 smoothness, as a result of which the visiting insect is precipitated to the bottom of the 

 pitcher. From this detentive area escape is rendered difficult by steep and narrow walls, 

 smooth or lined with downward-directed hairs; often, too, the falling insect is plunged into 

 a liquid which fills the lower portion of the pitcher's tube and which has the property of 

 quickly terminating the struggles of an entrapped insect, so that within a few seconds all 

 efforts toward escape cease, and rarely does even the strongest insect succeed in gnawing its 

 way out through the pitcher's walls. 



This pitcher liquid, originally a natural secretion of the plant, but eventually more or 

 less contaminated and diluted from outside, is thus an important part of the insect trap. Its 

 continued effectiveness is enhanced by its rapid increase in volume in response to the presence 

 of nutrient matter; that is, the liquid increases in quantity as insects are captured, and experi- 

 mentally, to a surprising degree, when milk or raw meat, for example, is introduced into a 

 pitcher. In most species the pitcher liquor contains a proteolytic enzyme, similar in its 

 properties to the digestive enzymes of the mammalian stomach; steeped in this stupefying 

 and digestive liquid, the softer parts of the entrapped insects are quickly dissolved. Absorption 

 by the plant from the fluid contents of the pitcher has been demonstrated by careful 

 experiment and chemical study. 



Added to the cumulative evidence of these characters of the pitcherplants and other 



2-5 



