478 SYNOPTIC COLLECTION. 



ing either the eggs, larvae, pupae, or adults of other 

 insects, and in this way proving more beneficial to man 

 than almost any other group. It is indeed singular that 

 a whole family should take upon itself so completely the 

 parasitic habit ; and since this habit is far removed from 

 the primitive habits of primitive insects, so the structure 

 of these parasites is very different from that of their 

 Thysanuran ancestors. 



Thalessa lunator Fabr. (No. 1220, 9 ; No. 1221, g) 

 is one of our largest species. The extremely long ovi- 

 positor of the female (No. 1220), measuring from three to 

 five inches, consists of three parts and is encased in a 

 sheath made of two parts. By means of this awl-like 

 organ Thalessa reaches the burrow of the horntail, Tremex 

 cohimba Linn, and deposits its egg. The footless larva 

 on hatching attaches itself to the Tremex larva and sucks 

 its blood. According to one observer quoted by Lintner 1 

 Thalessa has been seen "sitting upon the bark where per- 

 forations mark the exits of previous occupants and also 

 running around until she finds a promising spot, as, for 

 instance, the hole made by a Tremex in depositing her 

 eggs." This hole she sometimes takes advantage of, 

 probing it with her ovipositor until the burrow is reached. 

 Riley has shown that the instinct which guides Thalessa 

 to a Tremex burrow is not unerring, but more or less 

 experimental work is done and often mistakes are made. 



Those ichneumons that lay their eggs in caterpillars 

 and the like do not need long ovipositors and therefore 

 this organ is shortened (No. 1222, Ichneumon grandis 

 Brulte). 



The social Hymenoptera or the wasps, bees, and ants, 

 are remarkable animals when considered from a physio- 

 logical point of view. Their skill, intelligence, and their 

 power to improvise implements and use them, challenge 

 the profoundest thought of the biologist. Among all the 



!4th Rep. Ins. N. Y., 1888, p. 38. 



