FLAX CATERPILLARS IN KENYA COLONY. 101 



but tlie increase in tlieir numbers was entirely insufficient to account for the reduction 

 in the numbers of caterpiUars. Some may possilily have pupated in the {ground (l)ut 

 compare with Field No. 2). 



Field No. 2. — This held was on the same farm as No. I and ([uite near to it. The 

 flax was nearly ready for pulling. The caterpillars, which were especially attacking 

 the seed-bolls, were rather less numerous than in Field No. 1, but they were rather 

 older and many cocoons had already been spun. The field was treated in the same 

 way as the other, but after four days no reduction was found in the number of 

 caterpillars. 



Field No. 3. — In this field on a neighbouring farm the flax was in flower. The 

 caterpillars were about as numerous as in Field No. 1. The field had been gone over 

 about six times a day, but instead of rope, reim (twisted hide) had been used, the 

 reim being much less heavy than the rope used on the first two fields. The reduction 

 in the number of caterpillars was about 35 per cent., as against about 75 per cent, 

 on Field No. 1 . 



Field No. 4. — As a check on the counts in the above three fields, counts were made 

 on another field, which had not quite reached the flowering stage, where the caterpillars 

 were not very plentiful. They were of fair size, but no cocoons were found. This 

 field was not roped. The number of caterpillars found after the four days' interval 

 was almost identical with that found previously. 



Field No. 5. — On this field of flax in flower there was a very bad outbreak. Many 

 of the caterpillars were in the last stage and cocoons were very plentiful. On part of 

 this field the flax had been badly stripped of leaves before the outbreak was ob.served, 

 and roping started, but caterpillars, while less numerous, were still present in large 

 numbers in other parts of the field, and in these parts not many cocoons were seen. 

 After four days of roping, with ropes about an inch in diameter, dragged through the 

 flax half a dozen times a day, the caterpillars were appreciably fewer than previously 

 on part of the field where the crop had not been seriously damaged, but the roping 

 had not prevented the badly stripped area from increasing in size. 



In the last field, some observations were made in order to try to determine just in 

 what way the roping may bring about a reduction in the numbers of the caterpillars. 

 Dead or injured caterpillars on the ground are not objects which readily catch the 

 eye, but when a search was made some injured caterpillars were found. One large 

 caterpillar which could just wriggle a little was found, and an hour later it was unable 

 to move, being apparently dead. Another caterpillar, not very large, was found on 

 the ground, moving only just a little ; it did not make any attempt to climb up a 

 flax plant ; several small ants, one after the other, were seen to tackle it single-handed, 

 when it would wriggle, and each time they gave up the attempt ; but after an hour 

 and a quarter it was attacked by these ants in force and carried off. Other caterpillars, 

 some larger, some smaller, were seen to be attacked by ants successfully. In an area 

 of two square feet where particular search was made, six victims of ants were found. 

 One, which the ants had been watched carrying-off, was found an inch and a half below 

 the surface of the soil. Another, injured at the hind end, succeeded at the third 

 attempt in escaping from its a.ssailants up a flax stem, which it climbed about three 

 inches, but there it hung helpless from a leaf. It was found that a big healthy cater- 

 pillar was able to escape, even when placed in an ant-run, but half-grown healthy 

 caterpillars were overwhelmed and carried oft" by a crowd of ants. Very small 

 caterpillars were several times found being carried by only a single ant. 



Obviously, from the fact that great numbers of caterpillars are seen climbing up 

 the plants after being knocked oft" by the rope, the great majority escape after any 

 one passage of the rope, but if only a small percentage be mortally injured, or placed 

 at the mercy of ants, the cumulative effect would explain how the roping method 

 acts. Six per cent, of casualties each time the rope passes, is sufficient to explain the 

 figures recorded for Field No. 1 . 



