262 



Marvels of Insect Life. 



each cocoon would produce an ichneumon-wasp that would at once set to work to 

 check the numerical increase of the white butterflies. If we keep some of the cater- 

 pillars of these butterflies under observation we may see them visited bv little black 

 four-winged Insects, so minute as scarcely to be felt by the victim when thev alight. 

 One of these will pierce the skin of the caterpillar with the keen egg-placer, and 

 through it will pour a great number of eggs into the caterpillar's bodv. One of our 

 photographs shows over sixty chrysalids of another species of ichneumon, known 

 as a proctrotrupid, taken from a single chrysalis of the smaller white butterflv. 

 This, however, does not give a correct idea of the enormous number of ichneumon- 

 grubs that one caterpillar can support. From a caterpillar of the large white butterfly 

 not fewer than 1,200 of the little black microgasters have been reared. Sometimes 

 the grubs leave the caterpillar before it has had time to change to a chrvsalis, and 



may be seen actively spin- 

 ning loops of silk, which in 

 a short time are connected 

 to form oval cocoons. Other 

 species wait until the cater- 

 pillar has become a chrysalis, 

 when the\' in turn change, 

 and make their exit later as 

 winged Insects. 



Other species, such as 

 the straw-coloured ophion ^ 

 shown on page 263, are so 

 large that only a single grub 

 can be accommodated in a 

 caterpillar of large size. Often 

 the caterpillar that has been 

 parasitized by one of these 

 can be detected by a dis- 

 coloration where the skin has 

 been pierced to admit the 

 single egg. A favourite 

 victim of this species is the large caterpillar of the puss-moth, and the parasite 

 remains in it until the puss-caterpillar has constructed its hard cocoon. When 

 the puss-caterpillars of the next generation are attaining a size sufticient to endure 

 a lodger's drain upon their resources, the ophions break through the cocoons that 

 imprison them and lay their eggs in the cater})illars. Note the compressed, sickle- 

 shape of the body, as shown in the photograph. 



But not all the ichneumons are internal parasites. In some cases, as in the 

 girdled paniscus,^ the egg is laid on the outside of a caterpillar, but attached to 

 the skin. The grub never entirely quits the egg-shell, but retains a hold hv it^ 

 hinder parts, and also attaches itself by its mouth to the ^kin of the caterpillar, and 

 appears to absorb the juices of the latter through its skin. Newport, experimenting 

 with this ichneumon-grub and its host the caterpihar of the broom-moth, found tliat 



1 Ophioii luteuni. - I'.iniscus vir.i^'at us. 



Photo by} 



A Battery of Cocoons. 



[E. Step, F.L.S. 



Some species of ichneumon leave the all but empty skin of their victim as grubs, ami 

 spin their own cocoons. This species construct their cocoons in such admirable order 

 that they form a straight-sided mass as shown. The circular openings are cocoons 

 from which the ichneumons have escaped. Magnified four times. 



