OF SKLBORNK. 149 



There is an (Estrus, known in these parts to every 

 ploughboy ; which, because it is omitted by Linnaeus, 



thus attained a stage of its existence when the attacks of the black fly are 

 no longer to be dreaded, it is not even then to be regarded as absolutely safe. 

 In some seasons, particularly in those when the summer is marked by a 

 long continuance of drought, another pest is inflicted on the crop, which 

 is to the full as destructive as the ordinary fly. In the summer of 1835> 

 this enemy was active at Selborne, and many of the fields on the malm 

 lands were laid waste by its ravages : the only goodturnigs to be seen in 

 the district, in the autumn of that year, were in the neighbourhood of 

 Oakwoods, on the sandy lands near the Forest. Here, as elsewhere, 

 the crops on the chalky soils appear to have been most obnoxious to 

 injury ; although the damage was by no means limited to them. 



Mr. Yarrell has given to the Zoological Society some account of the 

 visitation of the black worm, as it was generally called, in 1835. Early 

 in July, he says, the " yellow fly" was seen upon the young turnips. It 

 was remembered by some that this was the fly which prevailed in 1818, 

 and which was followed by the caterpillars known by the name of the 

 ' blacks." The appearance of the perfect insect was quickly succeeded 

 by that of the black caterpillar, or turnip pest, feeding in myriads on the 

 leaves of the turnips, but leaving their fibres untouched. So complete 

 and so rapid was the destruction in some instances, that a whole field has 

 been found, in two or three days, to present only an assemblage of 

 skeletonized leaves ; and this too when the plants had attained a consider- 

 able size. The destruction of the leaves caused, in most cases, the loss of 

 the root also : and where the root did not altogether perish, it became pithy, 

 and of little comparative value. A second and even a third sowing were 

 necessary, in consequence of the destruction of the earlier crops ; and, so 

 extensive was the failure, that large importations from the continent were 

 required to supply the deficiency. The caterpillar, finally casting its 

 black skin and assuming a slaty appearance, buried itself in the ground, 

 forming a cocoon from which the perfect fly quickly emerged, filled with 

 eggs and prepared to renew the swarms of fresh depredators. By these 

 repeated broods the devastation was successively continued, till it was at 

 length put an end to on the occurrence of those heavy rains in September 

 by which the unusually dry and lengthened summer was terminated. 



The insect produced from the black caterpillar is a kind of saw-fly, or 

 Tenthredo, little more than a quarter of an inch in length, of a pale 

 yellow colour, with a black head and a black patch on each side of the 

 thorax: it is believed to be the Athalia Cent'tfolice, LEACH; but the 

 species of this genus resemble each other so nearly as to render the 

 discrimination of them difficult. 



A visitation of these pests in Norfolk, in 1782, was described by 

 Mr. Marshall in the following year, in a paper contributed by him to the 

 Philosophical Transactions. They are there spoken of under the name 

 of the black canker caterpillar. Many thousands of acres, on which a 



