AQUATIC MIDGES AND SOME RELATED INSECTS. 9 



SUBFAMILY CHIRONOMINyE. 



Croup I. — Chironomus lobiferus Say. 



In this first group the author wishes to consider as a type one of the chironomid larva 

 that seems to have departed most wide'ly from the more familiar examples. This species, 

 however, is capable of living in a loose mud burrow and of collecting and eating its 

 food directly from the surface of the accumulated debris about it, but this is not its most 

 characteristic method of feeding when living in competition with other species. 



HABITAT. 



The burrows of Chironomus lobiferus may be found on floating logs, at the bottoms 

 of ponds, or attached to stems, stumps, and other perpendicular surfaces. In these 

 habitats the larvae live by straining the fine particles from the water which passes 

 through their burrows. A still more unique mode of life is shown by C. lobiferus in the 

 readiness and frequency with which it penetrates the stems of aquatic plants. A list of 

 the plants attacked includes so nearly all the submerged aquatics that it is concluded 

 that the structure of the epidermis is the important limiting factor. 



The presence of larvae within a stem is easily recognized by two small round open- 

 ings through the epidermis which they make at either end of that portion of the tissue 

 occupied by their burrows. These openings enable the larvae to set up a current through 

 their burrows by throwing their bodies into an undulatory motion. In this way the larvae 

 are able to obtain food and carry on their respiratory processes at the same time. The 

 general behavior of Chironomus sparganii Kieffer [lobijerus(?)] larvae has been observed 

 and well described by Willem (1908). 



The general facts are as follows : The larvae are found in both dead and living stems 

 of Sparganium, in the softer tissue where the chlorophyll is lacking. They are commonly 

 located some 8 or 10 inches below the surface of the water. In the dead and especially 

 the well water-soaked stems of Sparganium they are to be found in abundance. Their 

 burrows communicate with the exterior by two small openings from one-quarter to one- 

 half millimeter in diameter. The openings are at varying distances from each other, but 

 usually measure in a rough way the relative lengths of the larvae, the average distances 

 being about 15 millimeters. 



The method by which the larvae penetrate these stems seems not to have been ob- 

 served nor questioned so far as the literature is concerned. In Group IV is discussed the 

 adaptation of the head of Chironomus brascnicc for burrowing, and evidence is given that 

 the penetration of the uninjured epidermis is a matter of very considerable difficulty. 

 The larvae of C. braseniec, however, show a unique adaptation to this procedure by 

 spinning a special silken arch by which they are able to apply pressure more advanta- 

 geously to their mouth parts. This phenomenon was not seen in a considerable series of 

 C. lobiferus larvae that were kept under observation for this purpose, and it is concluded 

 that this species has not yet developed such an adaptation. 



The experiments set up for the purpose of testing out the ability of a larva to enter an 

 uninjured stem were of two kinds: First, outdoor experiments with uninjured stems 

 fastened together as rafts and placed among the infested stems; and, second, small 

 sections of infested stems taken into the laboratory and placed in watch glasses, in which 



