296 F. M. HOWLETT. — A PRELIMINARY NOTE, ETC. 



but hide themselves in dark crevices and cracks, holding on by the processes 

 of the posterior part of the body so as to leave the head free for feed- 

 ing. On the approach of danger they will generally " sham dead," becoming 

 perfectly motionless. The older larvae are usually less active than the young 

 ones, and will sometimes remain motionless for hours together. In this condition 

 they are particularly difficult to see, the particles of earth and dirt which adhere 

 to the body-bristles making them harmonise in colour and texture with the 

 background. Although the larvae of all three species are thus inert, they are quite 

 capable of rapid and abrupt movement when irritated. On one occasion a small 

 mite was seen walking on the body of a larva (P. minutus) ; the larva remained quiet 

 until the mite reached the region of the head, but then started energetically 

 *' fighting " the mite by whipping up the tail and bringing its long caudal bristles 

 into play against the back of the head. Since the places in which the larvae generally 

 live are of a kind where there is likely to be risk from small wandering predators 

 and parasites such as mites, it is not improbable that one function of these very 

 curious caudal bristles is to serve as a means of active defence. It is also probable, 

 however, that as organs of touch they serve a useful purpose at all times, while there 

 is another curious habit of these larvae which might be supposed to have a bearing 

 on the use of the bristles. This is the habit of walking backwards which the larvae 

 possess and which they often exhibit ; no one who has seen them do this could deny 

 that the nodding plume of bristles in front gives a very strong impression that the 

 advancing tail is really a head, but it is unlikely that the normal enemies of the 

 larvae are sufficiently intellectual or fastidious to make the deception of practical 

 utility as a means of avoiding attack. 



There exists one simple bionomic character, the influence of temperature, which 

 also differentiates the species and has some practical importance. In this respect, 

 as in some others, argentipes seems more or less intermediate between papatasii and 

 minutus. 



The length of the life-history in a typical lot of each species is indicated in a 

 diagram (fig. 1). From this it will be seen that minutus, although its life-history is 

 considerably lengthened, breeds more or less continuously through the cold weather 

 at Pusa, where our observations have been made. P. argentipes larvae hatching 

 at the beginning of the cold weather may develop either quickly or slowly (even 

 larvae from the same batch of eggs) ; while P. papatasii larvae hatching at the 

 same time will remain as larvae until the following spring, whei;i they pupate and 

 emerge in late February or March according to the temperature. The interesting 

 case of argentipes recalls my experience with the eggs of Stegomyia scutellaris ; when 

 a batch is laid at the end of the autumn, one may find a certain number of the eggs 

 hatching out within a day or so, while others do not hatch, though they remain 

 alive and will hatch in the following spring if kept in water. If kept dry for a few 

 months they will hatch when placed in water. The cause of these variations in the 

 rate of development of late batches of eggs, or of larvae from the same batch of 

 eggs and kept in the same vessel, would form an interesting subject of study. 



