54 MUSTARD. [1900 



two pairs of abdominal sucker-feet. A very large number of our 

 common crop caterpillars have four pairs, and walk, or creep, evenly 

 onwards. Some of our most destructive orchard caterpillars have only 

 one pair of these abdominal sucker-feet; consequently, as the hinder 

 half of the creature has to be drawn up to the foremost before it pro- 

 ceeds on each step in its travels, it forms an upright arch, or "loop," 

 in walking, and is thence called a " looper." The Gamma caterpillars, 

 having two pairs, do not need to form a quite complete loop, and are 

 therefore known as semi-loopers, and the distinction is worth bearing 

 in mind, as a help towards identification.* 



When full-fed, the caterpillar changes to a dark-brown or black 

 chrysalis, visible through a woolly open-work cocoon, which it spins, 

 possibly on its food-plant, but very likely on any plant near, whether 

 cultivated or otherwise, and in bad attacks the cocoons are very notice- 

 able, as on corn, Dock, kc, aud especially on Thistles. In the past 

 season some excellent specimens of these net-work or woolly cocoons 

 were sent me, from which the moths, both in the case of the Mustard 

 and the Potato attacks, began to appear from the -Ith to the 6th of 

 August. 



There are, or may be, two broods yearly, of the second of which 

 the caterpillars live (according to German observation) through the 

 winter ; and moths apparently also occasionally hybernate. 



The moth, though not appearing often as a bad crop infestation, 

 is very common in summer and autumn, and is chiefly distinguishable 

 by its fore wings, which are about or upwards of an inch and a half in 

 expanse, and of a satiny glance, or sometimes of a purplish or coppery 

 lustre, with brown or grey markings, bearing in the centre of each a 

 pale or silvery figure like the letter •' Y," from which the moth takes 

 one of its popular names. 



The following notes which I was favoured with by Mr. H. L. 

 Lennard. of Preston, Hull, are of much valuable interest. It will be 

 seen that they give the date of first observation of caterpillars whilst 



* The colours appear to vary, or at times to vary with age. sometimes to be 

 of dark green with a mixture of brown, and sometimes they are considered to vary 

 in colour with that of the leafage on which they are feeding ; this presumably from 

 the leafage showing through the skin. A description has been given (see ' British 

 Butterflies and Moths,' vol. vi. pt. iii. pp. 112-114) of a smaller form of larva, only 

 about an inch in length, and darker in colour, from which such few moths as deve- 

 loped were smaller aud lighter than the ordinary species. It is especially mentioned 

 by the well-qualified entomological observer that he is satisfied the colouring of the 

 larva was "not due in anyway to disease or feebleness"'; otherwise from his 

 mention that "all the larvie, when full-grown, were very small"; also that 

 probably half of his '"died without spinning at all, and from those that did 

 spin and change to pupie, only one moth managed to emerge"' ; it might be con- 

 jectured that the specimens were not so much a variety as a diseased and stunted 

 form. 



