Triacanthagyna and Gynacantha 7 



swift and as well controlled, apparently, as is possible for the larger eyed 

 Gynacantha. Generalizations on the habits of flight of aeshnines are 

 dangerous even when a large amount of data is available, but it may be 

 mentioned that the equally large-eyed Neuraeschnas, on the single occasion 

 I observed them, were crepuscular with swift and well controlled flight. I 

 believe such crepuscular flight as is found in Gynacantha and Triacanthagyna 

 and possibly other aeshnine genera is a specialized habit related to the food 

 slupply. some approach, under favorable conditions, to which is seen in 

 Coryphaeschna, Aeshna, Boyeria, and probably other aeshnines, Tholymis 

 and Pantala among the libellulines, and Neurocordulia among the cordu- 

 lines. Certainly it is an adaptation found chiefly among the aeshnines and 

 possibly not present at all in the Zygoptera, though certain species are 

 noticeably most active late in the afternoon. 



Ecological notes: That there is some sensitive adjustment to their en- 

 vironment is indicated by the spotted distribution of even the most widely 

 ranging species of Gynacantha. For example. Palma Sola, \'enezuela, is in 

 a very level heavily forested region and lies about 35 meters above sea level. 

 By railroad it is about 37 kilometers from Tucacas on the coast. Here in 

 the evenings nervosa flew literally by hundreds or thousands. About 30 

 kilometers farther inland on the railroad lies the plantation Boqueron, at an 

 elevation of about 125 meters. In the vicinity are many beautiful streams 

 of dififerent sizes and character. There are extensive pastures and corn- 

 fields but closely surrounding these are forests as dense and of the same 

 general character as the forests about Palma Sola. The landscape is varied 

 with some low hills and the general result is a region apparently much richer 

 and certainly much more attractive than the region about Palma Sola, but 

 during eight evenings at Boqueron we saw not a single neri'osa though we 

 looked diligently for them. Cristalina lies far inland in Colombia, near 

 Puerto Berrio, which river port is about 164 leagues above Barranquilla. 

 The elevation of Cristalina is about 320 meters. In general the topography 

 roughly suggests the topography about Boqueron, though there is less flat 

 forest. In fact it differs from Boqueron about as Boqueron differs from 

 Palma Sola. But at Cristalina we found nervosa flying in about the same 

 numbers as we found them at Palma Sola. Why were they absent at 

 Boqueron? There is also the factor of seasonal distribution to consider. 

 We may expect this to become more evident as one leaves the equator. It 

 was conspicuously evident at i5-i6°N. at sea level at Puerto Barrios, Guate- 

 mala, where T. septima was abundant in May and June and entirely wanting, 

 that is, there were no great crepuscular flights, in January and February, 

 when none was seen. Generalizations as to where and when these aeshnines 

 may be found are therefore dangerous. They are essentially forest insects, 

 though the forest may be low and chaparral-like ; they require moist earth 

 for ovipositing, and rains or overflow must provide water for the larvae ; 

 species and individuals seem most numerous at comparatively low elevations 

 above sea level ; and they are essentially tropical. 



