A HISTORY OF DEVONSHIRE 



But the spider objects to the patronage and makes a further drop ; in a few seconds the fly follows 

 the object of her adoration and again touches the spider, and she, no doubt by instinct, knowing her 

 foe, resigns herself to her fate, and does not move. The fly turns round, walks backward until 

 within striking distance, and then thrusts her ovipositor into the thorax and deposits her egg. The 

 ichneumon egg is hatched in about forty-six hours, the larva taking about ten days in consuming 

 the unfortunate spider by suction. When feeding, it lies Sack-like across the spider's back till it 

 has almost consumed its victim ; when the larva finds the spider is getting inconveniently small 

 for it to rest upon, it attaches itself by the hooked tubercles with which its back is provided, to the 

 web the spider had previously made, so as to feed on the last remains of its victim, and then 

 make its cocoon. When the spider is emptied of nourishment, the legs and skin drop to the ground. 



The larva is footless, it has in place of legs eight sucking discs, and on its back eight tubercles 

 furnished with moveable hooks which can be withdrawn into the tubercles, the discs are for attach- 

 ing itself to the body of the spider, and the tubercles for attaching itself to the web. 



The larva, suspended by the back, has now to make itself a cocoon in which to pass the 

 pupa stage. The larva takes about three days to do this work. It is during this time the eight 

 tubercles on the back of the larva have to play such prominent parts, having to perform the work 

 of the claspers of an ordinary caterpillar. When the silken cord is to be released by the tubercle at- 

 tached to it, it is done by withdrawing the booklets into the tubercle, which at once becomes disengaged 

 and ready to make another attachment. The anal segment has important duties to perform while 

 the cocoon is making, by carrying the silken thread from the mouth into the corners, where the 

 blunt head of the caterpillar could not carry it, or adjust it to its satisfaction. The anal segment 

 was seen to be used, while the caterpillar was feeding, by bringing it to its mouth, for the purpose 

 of removing some muscular fibre that had got entangled about its mandible. When full-fed, the 

 larva is about three-eighths of an inch in length. The fly, Polysphincta tuberosa, Gravenhorst, is 

 mature and escapes from the cocoon in about twenty days. 



Parasitic flies after they are mature remain within their pupa-cases a few days, to strengthen 

 themselves to combat with life in the outer world. When sufficiently strong they proceed to make an 

 opening in the cocoon with their mandibles ; when completed they make their exit, and are able to at 

 once take flight ; there is no drying and stretching of wings as is the case with butterflies and moths. 



If it is absolutely necessary, which it surely is, that we should have parasites to keep down 

 the superabundance of insects, then it is also necessary to keep these parasites in check to counter- 

 balance the destruction constantly going on in the insect world, and these we have under the 

 designation of hyperparasites ; and they are not confined to one genus alone, although the whole 

 of the genus Mesochorus are hyperparasites. To carry on this work the hyperparasitic flies have to 

 discover larvae adapted to their several requirements ; that is, a lepidopterous or other larva must 

 contain parasitic larvae living within its body before the hyperparasite is able to keep up the con- 

 tinuity of its race ; and, as previously mentioned, the parasitic larva lives and feeds in what one may 

 say is the centre of its victim, with not the slightest outward visible sign of its existence within. 

 Therefore one might naturally presume that it would be safe from external attack; but such is 

 not the case : the possession of some specialized sense on the part of the hyperparasites enables 

 them to discover the parasitic larva concealed within the body of the caterpillar, and the egg 

 is quickly deposited. But it does not follow that the egg deposited always enters the parasitic 

 larva within, although the parent fly did its best to make it do so ; if not, the hyperparasitic egg, if 

 hatched, not having its proper food, cannot exist. 



In confirmation of this latter assertion, the writer desires to mention that on 30 May, 1880, 

 he observed a hyperparasite flitting about from leaf to leaf, keeping the antennae in constant 

 motion, evidently hunting about for a suitable place in which to perpetuate her race. After 

 waiting and watching the lady for some time, she came up to the object of her search, which 

 was a caterpillar of the magpie moth {Abraxas grossulariata, Linn.). After passing round it 

 several times to make sure everything was correct, she suddenly sprang on the unfortunate 

 caterpillar and thrust her ovipositor into the second segment, just below the dorsal line. The 

 caterpillar, during the operation, strongly objected to the proceeding, and painfully twisted itself 

 from side to side to get rid of the foe. The hyperparasite {Mesochorus olerum, Curtis) then 

 alighted on the leaf of a currant bush close by, she was duly boxed (captured), the caterpillar was 

 removed, fed up, and in due time the ichneumon larva left the caterpillar and spun up as 

 do ordinary larvae of the parasite (Casinari vidua, Gravenhorst), whose peculiar cocoon cannot be 

 mistaken for any other ; this was naturally expected ; but the surprise was that the maker of the 

 cocoon appeared instead of the hyperparasite M. olerum. By these remarks it will be perceived 

 the hyperparasite was correct in its knowledge that the magpie moth caterpillar contained, 

 hidden within, the ichneumon larva of which it was in search, but the egg failed to reach the 

 larva it was intended for. M. olerum is a common hyperparasite on C. vidua, and has often been 

 bred from the cocoon made by C. vidua. 



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