310 THE CANADIAN ENTOMOLOGIST. 



two grooved lines. Wings as in Tetrastic/ius, the nervures, except the 

 submarginal, dark fuscous. Abdomen sessile, depressed above, boat- 

 shaped beneath and terminating in a strong ovipositor that is fully half 

 the length of the abdomen. 



Hab. — Ottawa, Canada. 



Bred by Fletcher and Harrington from Dipterous larvfe, destroying 

 the seeds of Cirsium afve?ise, Scop. 



CNICUS DISCOLOR AS AN INSECT TRAP. 



BV W. S. BLATCHLEY, TERRE HAUTE, INDIANA. 



It is a well known fact that certain plants, as Silene antirrhina, L., 

 and allied species, exude a sticky, viscid substance on stalk or peduncle 

 for the purpose of preventing ants, small beetles, and other honey-loving 

 intruders, which are too small to aid effectively in fertilization, from 

 creeping up to the flower and robbing the honey-glands of their precious 

 nectar. Other plants, as the Sundews, Drosera rotundifolia, L . etc., 

 excrete a similar substance with which they attract insects, which are 

 caught and afterwards utilized as food by the plant. 



But no one, as far as the writer can ascertain, has called attention to 

 the fact that one of our common thistles, C?iicus discolor, Gray, has along 

 the middle of the outer surface of each of its involucral scales a large 

 gland whose viscid secretion is poured forth in abundance and is especi- 

 ally attractive to certain species of insects. It is true that Dr. Gray in 

 his Synoptical Flora, p. 402, mentions these glands and uses their presence 

 or absence as characters to aid in the determination of species, but he 

 says nothing of the substance which they secrete. 



On various occasions in the autumn of 1891, numerous insects were 

 observed by the writer crowded about the lower involucral scales of the 

 thistle mentioned, where they were evidently attracted by the excretion 

 there found. A closer examination always revealed that a number of the 

 smaller ones were prisoners, their feet having become entangled in the 

 viscid excretion, which had held them firmly, much as the pollen grains of 

 Asclepias hold at times our common honey bee. 



On Sept. 14 many flies and a number of specimens of a small green 



beetle, Diabrotica longlcornis, Say, which feeds upon the pollen of the 



thistle flowers, were found thus entangled and were dead, as were also 



three specimens of Phalatigidce. A number of them were so dry as to 



crumble into powder when touched, showing that they had been prisoners 



