IB 
COEN AND GEASS. 
and Merthyr Railway) the mountain brook running from the Fforch 
Mountains was thick with myriads of these caterpillars, which had 
been drowned by falling into it during their march across the side of 
the mountains. The Ystrad side of the Bwlch-y-Clawdd Mountains 
above Cwm Park were “ brown, as the result of recent fires ignited 
with a view to destroy the pests.” Near the summit the insects were 
observed, which moved down to the mountain-path from the burnt 
herbage with extraordinary rapidity. Some of them were secured, 
and (as above mentioned) specimens from the hordes were sent to 
myself for examination. 
On proceeding some miles towards Maisteg, leaving the Ogmore 
and Garw Yalleys on the left, everywhere caterpillars were swarming, 
and a large hole in the peat was observed in which thousands of the 
caterpillars had fallen and died. The Maindy and Bwllfa Mountains 
were alive with them, and, standing on the ridge above the Ogmore 
Valley, the smoke of the mountain fires was to be seen to the west, 
where attempts were being made to destroy the pests. 
Further details are given in this and in other accounts, of which 
the main points are—the great area attacked and the damage done ; 
the necessity of burning the surface to destroy or drive away the cater¬ 
pillars, and likewise the vast numbers found drowned where there was 
water to fall into; and also the quantities of rooks or crows which 
flocked to the infested area. 
All these points coincide with what has been reported of similar 
attacks elsewhere, but, as I am not aware of the geographical area of 
an attack ever having been so minutely recorded, I have thought it 
desirable to give it at length, with a map accompanying. 
The only available remedy for attack on this vast scale appears 
to be the one made use of, namely, firing the surface, and thus 
getting rid of great numbers of the caterpillars amongst the burning 
grass and heath, and other mountain plants which would help to feed 
the fire. 
The habit of the caterpillars of going right onwards, whether into 
streams, standing water, or otherwise, together with their activity in 
crawling in bodies away from the fired ground, might very possibly be 
utilised to direct the course of some of the hordes into a stream or 
other convenient end. 
On a moderate scale of attack it has been found to answer to turn 
pigs on the infested land, or plough the surface to turn the grass roots 
up with the caterpillars amongst them for the pigs to clear. 
