[ 109] 



few weeks of life constitute a period in which the insect is particularly 

 susceptible to the prevailing physical conditions. While difi&culty was 

 experienced in rearing large numbers of larvae from the egg to the 

 adult stage, no such difficulty was met with in rearing flies under the 

 same laboratory conditions from larvae collected in the field in late 

 winter. It may be suggested for example that wet weather in the end 

 of summer, and early autumn months, will favour the survival — apart 

 from natural enemies^-of greater numbers of larvae, and that con- 

 versely, prolonged drought will tend to kill ofE numbers of those hatched 

 about this time. In this connection it may be worth while to quote the 

 opinion held by some farmers in this area that a wet summer and 

 autumn foreshadows a plentiful supply of crane-fly in the following 

 year. 



The Larva on Farm Lands. 



Published references to the activities of the larva as far as I have 

 been able to trace them deal exclusively with instances of serious or 

 even excessive damage effected by these insects upon grass or com 

 crops. But in the course of the present investigation it has become 

 clear that Tipula larvae are very commonly present upon farm lands, 

 sometimes in considerable numbers, without their presence becoming 

 apparent. Cases of excessive damage have also been experienced, but 

 the following instance may be taken as an average experience under the 

 conditions named. It is quoted in full because it illustrates a number 

 of features related to the larval habits. 



These observations were made in the spring and summer of 1913, 

 upon the College farm at Craibstone. Search was made for the presence 

 of Tipula larvae in the end of March and beginning of April. The 

 weather was cold at the time, and the searches were not very fruitful. 

 The Woodlands field (Fig. 3) which was in grass at this time was selected 

 for enquiry, samples being dug up at a number of places, and the turf 

 thoroughly examined, but no Tipula larvae were obtained. Grey slugs 

 were particularly plentiful. This was on 3rd April. On the 19th, 

 ploughing was in progress and the plough was followed, samples of the 

 furrow were taken, disintegrated, and searched, but no larvae were 

 found in this way. Further search by two observers resulted in four 

 larvae being found. These were found under stones at the surface, 

 on the part not touched by the plough. After the field had been sown 

 and rolled it was again examined on the 29th, and larvae were now 

 found to be very numerous under the turf clods upon the surface. In 



