1890.] President' 's Address. xix 



happens, however, that the weevil larva has already reached an 

 advanced stage. It spins its cocoon also ; this cocoon is not made of 

 fine silk, but of earth or agglntinised wood, and impervious to the 

 feeble jaws of the Ichneumon. Both host and parasite will in that 

 case never emerge. But, if the Ichneumon is able to tear itself away 

 from its host, it will emerge on a fine day, wait a few moments to dry 

 its teguments ; opening its gauze wings it flies, awkward, partly 

 unconscious, with an effort that sends it against the first obstacle it 

 meets. It soon rights icself, however, and there it flies, heedless of 

 anything else but to seek a mate or wait for one, which will not be 

 long. 



I have just inspected a wine-farm. Seated on the stoep, my host 

 the farmer calls my attention to the state of his oak-trees, the leaves 

 of which are being devoured by a caterpillar. " I do not care for the 

 damage done to the oak-tree," quoth he, " but the rispers " — T am 

 afraid h^. added an adjective — " are attacking my guava-trees also." 

 Let us have a look ; and a look we have. There in clusters are the 

 caterpillars of Pachypessa Pythiocampa. 



" But what are these little white appendages on the body ? Are 

 they the eggs ?" asks my farmer friend. 



" Oh no ! Each of these little bags, cocoons in fact, contain a little 

 chrysalis of a four-winged fly. It was in its earlier stage a parasite of 

 the caterpillar, and at or about the time when it will come out of its 

 eocoon the caterpillar which is still alive will die." 



" So !" says my friend, looking rather incredulous. Yes, it is so, 

 and the caterpillar is carefully removed in a glass tube, tour weeks 

 afterwards the Ichneumon comes out ; it is a little fellow 10 mm. long. 

 But why an ovipositor two-thirds the length of the body ? The eggs 

 are to be laid under the skin ; why such a length ? I build an 

 hypothesis. Let us find out whether observations in situ will vouch 

 for its accuracy. Here I have before me several clusters of the cater- 

 pillars. I espy an Ichneumon ; there she comes, alights upon the 

 back of the caterpillar, and moves about a little, but with signs of 

 awkwardness. Why ? Because the future host is covered with long 

 tufts of hooked hairs. Were the ovipositor too short the Ichneumon 

 eould not reach the skin. My hypothesis proves true. I have not 

 seen tire Hymenopteran insect actually laying the eggs, nor have I 

 been able to detect the eggs under the skin of the host, but I saw her 

 puncturing and the caterpillar proved by its sudden jerk that the 

 puncture was felt. The action is repeated three times. 



These clusters of Pythiocampa caterpillars are capital subjects for 

 observation. Here comes an Ichneumon. She makes her punctures 

 and, certain that her progeny will find an abundant and suitable store 

 of food, flies away, contented, I presume. I capture her before she has 



