250 A NATURALIST IN BORNEO 



thousands of Fire-Flies, small beetles of the family Lam- 

 pyridce ; and I observed that the light emitted by these 

 little creatures pulsated in a regular synchronous 

 rhythm, so that at one moment the tree would be 

 one blaze of light, whilst at another the light would 

 be dim and uncertain. 1 This concerted action of 

 thousands of insects is very remarkable and not easy 

 of explanation. Another instance of it was mentioned 

 by Cox ; certain ants that are found very frequently 

 proceeding in columns along the floor of the jungle, 

 when alarmed, knock their heads against the leaves or 

 dead sticks which they happen to be traversing ; every 

 member of the community makes the necessary move- 

 ment at the same time, and as the movements are 

 rapid a distinct loud rattling sound is produced. In 

 this case the action is probably a danger-signal, and 

 we can understand theoretically at any rate how it 

 was brought about. But the value to the species of 

 the rhythmic-light pulsation of the Fire-Flies is not 

 obvious, and as it is doubtful if the emission of phos- 

 phorescent light is under the control of the insects, or 

 is merely a simple automatic process of metabolism its 

 synchronism is a most puzzling fact 2 [Note 19, p. 316]. 

 An early start was made next morning, and we had 

 not proceeded very far on our way when we were 

 overtaken by a light canoe poled along at a rare pace 



1 Also observed by Dr. N. Annandale at Kuala Patani (P.Z.S., 

 1900, p. 865). Dr. Annandale states that the larger bluer lights 

 of three individuals seated together pulsated with a rhythm dif- 

 ferent from that of the hundreds of others, with smaller lights, 

 upon the same large tree by the river-bank. E. B. P. 



2 There can be no doubt that the light is under the control 

 of the nervous system. See the examples under " Fire-flies " and 

 "Luminous beetles" in Longstaff's Butterfly-hunting. E. B. P. 



