THE MAGPIE MOTH AND ITS PARASITES 



1 109 



the egg there hatches a small 

 maggot which penetrates the skin 

 of the caterpillar, and feeds in- 

 ternally on that insect until its 

 development is complete. The 

 larva develops a ravenous appe- 

 tite, but the nourishment that it 

 absorbs all goes to benefit its in- 

 ternal boarders. Finally, when the 

 caterpillar should change into a 

 chrysalis, it usually has about 

 sufticient strength left to construct 

 its cocoon, which is the closing 

 scene of its life. The parasites 

 within then consume the vital 

 parts of their host, and this final 

 meal usually sufftces to complete 

 their development, whereupon they 

 break through the skin of the 

 caterpillar that has reared them, 

 and quickly change into pupae 

 with the silken cocoon, as shown 

 in the lower example on the left 

 of p. 1108. 



Not infrequently amongst the 

 bushes where Tachina flies are 

 abundant the parasitic Ichneumon 

 flies will also be found. These are 

 hymenopterous insects, possessing, 

 Uke wasps and bees, two pairs of 

 wings, a feature which readily dis- 

 tinguishes them from the dipterous, or two- 

 winged. Tachina flies. The Ichneumon files 

 may be recognised by their active move- 

 ments amongst the leaves, their long 

 antennae continually twitching and qui- 

 vering with excitement as it were, while 

 they seek for caterpillar victims on which 

 to deposit their eggs ; for although they 

 belong to an entirely different group of 

 insects to that of the Tachina flies, yet 

 their method of attacking leaf-eating 

 caterpillars for egg-depositing purposes, 

 and the subsequent development of the 

 larvae, is very similar. 



The Ichneumon flies, however, have 

 probably attained a much higher evolu- 

 tion than the Tachina flies, for the latter 

 will attack caterpillars of various species 

 indiscriminately, and also the larvae of 

 beetles, humble-bees, wasps, and insects 

 of other orders ; and not infrequently they 

 deposit more eggs on a larva than its 

 substance will provide for their maggots ; 

 or they will even place their eggs on a 

 caterpillar that is about to moult its 



THE MAGPIE MOTH JUST EMERGED FROM ITS 

 CHRYSALIS. 



skin, with the result that the \'oung grubs 

 perish when hatched from the eggs. 



The more highly evolved Ichneumon 

 flies, however, rarely make such errors ; in- 

 deed, a particular genus or species of these 

 parasites will sometimes prey upon only a 

 certain family of insects, so that a cater- 

 pillar may have its special Ichneumon ; or, 

 if it is an abundant species, it may have 

 several kinds of Ichneumons, which 

 patronise it as their special host for the 

 rearing of their young. 



From some of the pupae of the Magpie 

 Moth under observation in the experi- 

 ment pre\'iously referred to, the Ichneu- 

 mon species illustrated on pp. 1106 and 

 1 108 emerged, one fly only from each moth 

 pupa. The slender curved waist attached 

 to the lower ])art of the thorax, the long 

 and ]i()inted antennre. and the fore-wings 

 bearing a dark-coloured triangular s])()t, are 

 all features which show well on p. 1 106, and 

 which should be observed by all amateur 

 entomologists desirous of distinguishing 

 these insects. 



