10 Intrnors NarurAL History SurvEY BULLETIN 
ment of bilineata, and that species is not 
known to have developed there subsequently. 
Many adult females of Tortopus primus 
a trap light in Urbana, on 
1943. These still 
eggs. There is no locality 
were taken in 
August 13, females 
carried their 
where this species is known to breed within 
Vol. 26, Art. 1 
The length of nymphal life is so long and 
the nymphs are so frail that usually may- 
flies cannot be reared from eggs to adults 
without great loss of life. If mature or 
nearly mature nymphs whose wingpads show 
signs of darkening can be collected for the 
purpose of rearing, the number of deaths 
Fig. 6.—Siphlonurus marshalli adult being removed from a rearing pan. 
a radius of 20 miles from Urbana. The 
most likely source of this typically large- 
river species was the Vermilion River, 30 
air-line miles away, or the Wabash River 
in Indiana, almost 50 miles away. 
Rearing Mayflies 
Although the classification of the may- 
flies is based almost entirely on the adults, 
it is the nymphs which are most often taken 
in aquatic collecting or limnological work. 
In many instances, the generic and specific 
differences are much more distinct in the 
nymphs than in the adults. In order to be 
certain of their identity, it is necessary to 
rear the adults from the immature forms, 
but for most purposes of identification the 
association of mature nymph and adult is 
adequate. 
can be greatly reduced. Such nymphs are in 
the last instar, or at most only a molt or 
two removed from it. 
Mayflies which spend all or the latter 
part of their nymphal existences in still 
water can be easily and successfully reared 
from a late instar to the adult form in 
shallow pans. Such mayflies are Callibaetis, 
Siphlonurus, Leptophlebia, Paraleptophlebia, 
Stenonema, Heptagenia, all the Caenidae, 
most Ephemeridae, and some . species of 
Baetis. 
The rearing pans may be circular, flat- 
bottomed, enameled pans approximately 10 
inches in diameter and 4 inches deep. A 
large, flat rock should be put in each pan 
and water from the place where the nymphs 
were collected added to a depth of not over 
1 inch. The rock should be of a size to 
