122 Qiteries and Answers. 



attentive observers of the very common cabbage caterpillar (Pontio! 

 brassicEe) that when it ceases to feed, and leaves its native cabbage to 

 creep up walls and palings, it is often transformed into a group of little 

 balls of silk, of a fine texture, and a beautiful canary yellow colour ; from 

 each of which there issues, in process of time, a small four-winged fly 

 (Microgaster glomeratus Sj^inola), of a black colour, except the legs, which 

 are yellow. By breeding these flies in a state of confinement, and intro- 

 ducing to them some cabbage caterpillars, their proceedings in depositing 

 their eggs may be observed. We have more than once seen one of these 

 little flies select a caterpillar, and perch upon its back, holding her oviposi- 

 tor ready brandished to plunge between the rings which she seems to 

 prefer. When she has thus begun laying her eggs, she does not readily 

 take alarm ; but, as Reaumur justly remarks, v/ill permit an observer to 

 approach her with a magnifying glass of a very short focus. Having depo- 

 sited one egg, she withdraws her ovipositor, and again plunges it with 

 another egg into a different part of the body of the caterpillar, till she has 

 laid in all about thirty eggs. It is not a little remarkable that the poor 

 caterpillar, whose body is thus pierced with so many v/ounds, seems to 

 bear it very patiently, and does not turn upon the fly, as he would be cer- 

 tain to do upon another caterpillar should it venture to pinch him ,• a 

 circumstance by no means unusual. Sometimes, indeed, he gives a slight 

 jerk; but the fly does not appear to be at all incommoded by the intimation 

 that her presence is disagreeable. 



" The eggs, it may be remarked, are thrust sufficiently deep to prevent 

 their being thrown off when the caterpillar casts its skin ; and, being in due 

 time hatched, the grubs feed in concert on the living body of the caterpil- 

 lar. The most wonderful circumstance, indeed, of the whole phenome- 

 non, is the instinct with which the grubs are evidently guided to avoid 

 devouring any vital part, so that they may not kill the caterpillar, as in 

 that case it would be useless to them for food. When full grown, they 

 even eat their way through the skin of the caterpillar without killing it ; 

 though it generally dies in a few days, without moving far from the place 

 where the grubs have spun their group of silken cocoons in which to pass 

 the winter." 



The above insect has long ago been described and figured by Albin, in 

 his History of English Insects, plate 1.; which figure also has been in part 

 exactly copied by Wilkes in his English Moths and Butterflies (see his plate 

 of the large garden white butterfly). As the Microgaster is the destroyer 

 of that " pest of gardens " Pontic brassiere, it may be considered a bene- 

 ficial insect. 



Very many other lepidopterous larvae are subject to be preyed upon by 

 parasites analogous to Microgaster glomeratus, and thus occasionally cause 

 no small disappointment to the breeders of insects, who instead of seeing a 

 brilliant butterfly proceed from a chrysalis, as they naturally expected, are 

 presented in its room with a number of small flies. I once fed in con- 

 finement a caterpillar of Lasiociimpa quercus Stephens, large eggar moth, 

 which, after having spun its cocoon, and changed to a pupa, in due time 

 produced a host of small ichneumons, with long ovipositors, somewhat 

 resembling /chneumon manifestator in miniature. The generation of these 

 parasites was a subject which seems to have greatly perplexed our eai'lier 

 entomologists : " mira imo vix credibilia aut ante audita *, " are the woi-ds 

 of Joannes Goedartius, in reference to the above Mici'ogaster ; and after 

 mentioning the case of a second and still different parasite, which he reared 

 from the same species of the cabbage butterfly, he thus expresses his astonish- 



* " Wonderful things, nay scarce credible or before heard of," 



