May, 1953 
project partly above the water and thus 
provide a place on which an adult may 
emerge, fig. 6. A few rotting leaves or 
other detritus from the water where the 
nymphs were found should also be added 
to each pan to provide food. Care must 
be taken to have the pan, rock, and water 
all at the same temperature as the water 
from which the nymphs were collected. 
The nymphs may be taken from the pool 
or stream with a dipnet, or simply picked 
off rocks or other objects submerged in the 
water. They must be handled with the 
greatest care, as they are easily injured, 
always with fatal results. They may be 
kept in glass jars or cap vials partly filled 
with water until they can be transferred to 
the rearing pans. These temporary storage 
jars or vials must be kept cool, preferably 
by being partly immersed in the water where 
collecting is being done. 
An effort should be made to sort the 
nymphs to species, using the obvious charac- 
ters that can be seen with a hand lens. 
Part of each collection of a species should 
be preserved in alcohol at the time the other 
specimens are placed in the pans for rear- 
ing. An accession number should be given 
to each lot of specimens so that the adults, 
when secured, can unquestionably be as- 
sociated with their nymphs. 
The rearing pans containing the nymphs 
should be covered with a screen-wire or 
cheesecloth top to provide a place for the 
adults to rest after they have emerged and, 
also, to prevent their escape. “The pans can 
be transported to any convenient and suit- 
able place for observation, but must be 
kept cool and protected from the direct 
rays of the sun. An outdoor, open-air 
insectary, if cool and shaded, is an ideal place 
for them. A cool basement also will serve. 
Many of the mayflies for this report were 
reared at the fish hatchery of the Illinois 
Department of Conservation at Spring 
Grove, Illinois. 
If more than a day or two elapses be- 
tween the time the living nymphs are col- 
lected and the time subimagoes begin to 
appear, it is advisable to change the water 
in the rearing pans. This can be done by 
dipping out part of the water in each pan 
and replacing it with aerated, unchlorinated 
water of the same temperature. 
When the subimagoes emerge, each speci- 
men should be removed to a cap vial or other 
Burks: THE MAyertigss or ILLINOIS 11 
similar glass jar in which one moderate- 
sized green leaf has been placed. The cap 
of this container must not make an_air- 
tight seal. The subimago has to lose water 
during the subimaginal stage, but the loss 
must not be too rapid. The leaf will main- 
tain the humidity at a satisfactory level, 
while the loose cover on the container will 
permit the loss of water vapor by diffusion. 
If water is allowed to condense on the in- 
side of the container, the subimago will 
almost certainly die without shedding the 
subimaginal pellicle. 
The subimaginal skin will be shed usually 
within 24 to 36 hours, although, at very 
low temperatures, the subimago stage may 
last 2 or 3 days. When the adults emerge, 
they should be killed and mounted on pins. 
Notes should be made on the colors of the 
eyes and body of each specimen at the 
time of its death. The shed nymphal and 
subimaginal exuviae should be preserved in 
alcohol and be given the same lot accession 
numbers as the respective preserved nymphs. 
The reared adults should be studied care- 
fully to determine if all the specimens in 
each lot actually are of but a single species. 
The nymphs associated with each lot should 
also be studied critically at this time to 
determine if a pure culture of a single 
species is represented. “The nymphs, the 
nymphal and subimaginal exuviae, and the 
adults should now be clearly and perma- 
nently labeled in such a way that there will 
never be doubts, in the future, as to the 
correct association of nymphal and adult 
specimens. 
Some mayflies, such as [sonychia, Ephem- 
erella, Ameletus, some species of Baetis, 
and Baetisca, cannot be reared successfully 
in pans. However, they can be reared in 
screen-wire cages partly submerged in the 
waters in which the nymphs live. When 
the subimagoes appear in these cages, they 
can be removed to cap vials, where the 
adults will emerge. The only real disad- 
vantage of this method is that it requires 
that much time be spent in the field and 
makes difficult the finding of the shed nymph- 
al skins intact. 
Phillips (1930) was able to rear most of 
the New Zealand mayflies in laboratory 
aquariums, but I have had very poor results 
in my attempts to rear Illinois mayflies by 
this method. 
In the past, many associations of nymphs 
