256 



BULLETIN Olf THE BUREAU OF^ I^ISHERIES. 



However they may be laid, the eggs hatch quickly, and the ponds are swarming 

 during the summer time with nymphs of all sizes and kinds. These nymphs have long 

 masks which fold back beneath the head and thorax, like those of the dragonfly nymphs. 

 But in place of the rectal respiratory apparatus of the latter, they carry three external 

 tracheal gills at the posterior end of the abdomen. These are flattened laterally and 

 are usually about half the length of the abdomen, their size and shape furnishing one 

 means of identifying the species. 



Their food is similar to that of the dragon nymphs, but contains a larger percentage 

 of small animals, as would be expected (table, p. 201). One such nymph was seen by 

 Williamson (1899, p. 234) clinging to a dead catfish and evidently feeding on its flesh. 



ARGIA APICALIS (Say). 



Agrion apicalis Say, Jour. Acad. Nat. Sci., Phila., 1839, p. 40. 



The male imagos of this species never become pruinose like putrida; one was secured from pond 5, in 

 which the blue of segment 8 was W-shaped and restricted to the base of the segment, like that in translata. 



The imagos were observed by Needham (1903, p. 242) at Galesburg, 111., "feeding voraciously on 

 adult Chironomids. " The nymphs were not found at all in the ponds, but were fairly common in the 

 river. They do not travel far when ready for transformation, but the skins are always found within a few 

 inches of the v/ater's edge. 



ARGIA MCESTA PUTRIDA (Hagen). 



Agrion putridum Hagen, Synop. Neurop. N. A., 1861, p. 96. 



The largest species of the genus; does not breed commonly in the ponds, but is very plentiful along 

 the river. The imagos eat large numbers of mayflies, and when the latter are emerging almost every 

 Argia, male and female, may be found munching one. The males quickly become pruinose, fading into a 

 uniform bluish gray, but the colors are usually restored on immersion in alcohol. 



The nymphs are numerous in the river, but only one or two were fotmd in the ponds, and but few 

 imagos were seen around the ponds. When ready for transformation the nymphs often go long dis- 

 tances from the water and even climb rough-barked trees. Ten skins were taken from the trunk of a 

 large willow tree 60 feet from the water, and with them were found half a dozen skins of Lihellula luctuosa, 



AGRION (CALOPTERYX) MACULATUM (Beauvois). 



Agrion maculata Beauvois, Ins. Afr. Amer., 1805, p. 85. 



This beautiful damselfly is restricted to shady running water and is found only along a small brook 

 one-fourth of a mile above the station. It sticks close to its haunts, although a male was seen one day 

 fluttering along the shores of the ponds. Such visits, however, are only accidental, and the species does 

 not enter into the life of the ponds to any appreciable degree. 



ThK Genus Knali^agma. — Enallagma and Ischnura females, after inserting 8 or 10 

 eggs into the tissue of some plant, have a habit of stopping and straightening out the 

 abdomen and stretching it, much as one stretches his fingers after prolonged writing. 

 Evidently it requires considerable effort to thrust the ovipositor into the plant tissue, 

 and since the abdomen is curved during the process it relieves the strain to straighten 

 and stretch it. 



Two Enallagma females were observed on July 26 depositing their eggs. During 

 the process each came in contact with a partially drowned damselfly floating in the 

 water and tossed about by the waves, which they seized, pulled out of the water and ate. 



Here in the fishponds the Enallagma females seem to prefer the leaves of the crex 

 grass as tissue in which to deposit their eggs. When the leaves break and fall over into 

 the water, the part distal to the break dies and becomes apparently of just the right 

 consistency to suit these damselflies, and nearly every such leaf contains eggs. 



