and adults have been made by the process 
of relating adults taken by sweeping vegeta- 
tion around bodies of water with mature 
nymphs found in those waters at the same 
time. This method has led to so many 
misassociations that it should be followed 
only as a last resort, and the results should 
always be viewed with suspicion. 
Collecting and Preserving 
Both nymphs and adults must be collected 
very carefully if intact specimens are to be 
secured. The most valuable adult speci- 
mens are those reared from nymphs. Rear- 
ing not only yields a definite association of 
the nymph and the adult form but makes 
possible a collection of well-preserved speci- 
mens. 
Collecting at lights will yield the largest 
number of adults. Although usually speci- 
mens taken at light traps are in very poor 
condition, some very worth-while Illinois 
records have been secured by these devices. 
Careful sweeping of the vegetation near 
bodies of water will yield much valuable 
adult material. Subimagoes secured by 
the same means should be placed in cap 
vials so that the adults can emerge a day 
or so later. 
Experience has shown that adult mayfly 
specimens are best preserved dry, on pins. 
Each specimen may be pinned through the 
thorax from dorsum to venter with the 
wings spread in the conventional manner 
for entomological specimens, or it may be 
pinned on the side, with the wings to the 
left, the pin being inserted through the 
pleura of the thorax. The latter method 
is the more rapid, and the specimens, al- 
though perhaps not so neat in appearance, 
are more easily handled for study and can 
be stored in smaller space. 
The wings may be spread during the dry- 
ing process, without the use of a conven- 
tional spreading board, in the following 
manner. A square piece of 50-pound ledger 
paper, as large as the maximum wing ex- 
panse, when placed on the pin above the 
specimen will serve to hold the wings out- 
spread at the proper angle during the 2 
or 3 days required for drying. Another 
piece of the same weight paper of equivalent 
width, but twice as long, pushed up on the 
pin from below, will serve to hold the caudal 
filaments and fore legs at the proper ex- 
tension. Extremely small specimens, such 
12 Intinois NaturAL History Survey BULLETIN 
Vol. 26, Art. 1 
as those of most species of Caenis, may be 
mounted on card points. 
If a long series of adult mayflies is avail- 
able, it is desirable to preserve some dry 
and some in ethyl alcohol. Dry specimens 
retain their color characters longer than 
those preserved in alcohol. Specimens I 
have seen that were collected by Benjamin 
D. Walsh of Rock Island, Illinois, and pre- 
served dry for more than 80 years show 
most of the color characters fairly well. 
In alcohol, the colors fade so rapidly that 
10-year-old specimens in many genera are 
almost impossible to identify. Specimens in 
85 per cent alcohol retain their color longer 
than those in 70 per cent alcohol, but, after 
storage in 85 per cent alcohol for several 
years, specimens become so hardened that 
it is almost impossible to make satisfactory 
slide mounts of the genitalia. Although 
alcohol is not satisfactory in some respects, 
it provides an easy method of preservation 
and permits compact storage of large series 
taken at one time and place, and, in some 
instances, is better for the study of structural 
characters. 
No matter how preserved, the adult speci- 
mens are extremely fragile and must be 
handled with the greatest care. Specimens. 
whether dry or in alcohol, should be stored 
so that they are not exposed to the direct 
rays of sunlight, as light quickly bleaches 
them. 
If it is ever desirable to preserve subi- 
magoes, they may be preserved in 70 per 
cent ethyl alcohol, as the colors of subi- 
magoes are usually unimportant. Then, 
at any later date, the adult genitalia of such 
specimens may be dissected out of the sub- 
imaginal pellicles and be cleared and 
mounted in the same fashion as those from 
any adult specimens. 
Nymphal specimens may be picked from 
rocks or other objects in the water or col- 
lected from the water itself by careful 
dipping with an aquatic dipnet. In running 
water, large numbers of specimens may be 
secured if a seine or dipnet is held, in the 
current and the rocks, gravel, and other 
objects on the bottom upstream from the 
net are carefully turned over. The nymphs 
will release their holds on these objects and 
the current will carry them into the net. 
Nymphs and exuviae are best preserved 
in 70 per cent ethyl alcohol. Preserving 
mixtures containing acetic acid or glycerin 
