AQUATIC MIDGES AND SOME RELATED INSECTS. 25 



and the normal conditions maintained for several days. Careful observations showed 

 no signs of the larvae having begun burrows. They were then allowed to enter the 

 water beneath the leaf where they lived for several weeks, but failed to develop, even 

 though a miscellaneous supply of aquatic organisms was furnished. Several of the 

 larvae died and the experiment was abandoned after two months' observation. 



Just how the very young larvae maintain themselves is still undetermined. A 

 thorough search in the early spring before the leaves of Castalia or Brasenia had reached 

 the surface failed to reveal the presence of any of the larvae on the roots, stems, or leaves 

 of these, their characteristic host plants, or of any of the other near-by aquatic vegetation. 

 From the facts that none of the small larvae succeeded in penetrating the leaves under 

 laboratory conditions, that only large larvae were found in all the burrows opened, 

 and that the burrows are of a uniform width in practically all cases, it seems probable 

 that the larvae do not enter the burrows before mid-larval life (figs. 20, 21, 22). 



The author has been unable to make any direct observations on the length of 

 time spent in feeding on the leaves, as the larvae are not to be found in any of the 

 apparently similar aquatic situations about Ithaca and when brought into the laboratory 

 on leaves frequently leave their old burrows and start new ones. This confusion, 

 together with the writer's inability to rear the young under laboratory conditions, 

 forced him to use indirect means in determining the length of time spent in feeding on 

 the leaf tissue. Late in the season a dozen leaves containing active larvae were each 

 labeled by pinning a square piece of paper so that a marked corner came opposite the 

 end of the burrow. The label carried the number of the larva, and the rate of progress 

 was measured daily. These results showed that not more than 10 days on the average 

 would be required to construct a burrow of average length, while the larva that made 

 the greatest progress would not have required more than seven days. Subsequent 

 examination of these larvae showed 100 per cent infested with a Gordian worm, so the 

 results are doubtless inaccurate, although all larvae that ceased burrowing after a day 

 or two were omitted in making up the average. 



The larva transforms to a pupa on the leaf where it has been feeding. The pupal 

 chamber can often be seen at the end of a burrow 2 inches in length on the leaves of 

 Brasenia and somewhat shorter on the leaves of Castalia. A burrow of this length 

 represents the work as a rule of a single individual. The pupal chamber can be easily 

 picked out because of its club-shaped appearance (fig. 24), the big portion being at the 

 end of the burrow. The pupal chamber is, however, often completely separated from 

 the ordinary burrow, suggesting a vagrant tendency on the part of the larva just before 

 pupation. When separated from the larval burrow it has the same general shape and 

 appearance as when attached. It is but little longer than the pupa and is in rough 

 agreement with it in general outline. The pupa lies in this burrow with the head next 

 to the large open end. When ready to transform it wriggles through this opening and 

 the imago escapes. The pupal molt is usually ft with the thoracic part projecting 

 from the pupal chamber (fig. 24) . The length of lme spent as a pupa is about five days, 

 varying considerably with the temperature and the condition of the individual pupa and 

 the larva from which it transforms. 



The adults, both males and females, were found among the bushes and underbrush 

 along the banks, and several were shaken from the tops of trees 6 to 8 feet high. The 



