THE WESTERN GRASS-STEM SAWFLY. 19 
Elymus condensatus , growing from plants that had been browsed by 
cattle and had thrown up fresh green stalks. 
Mr. Norman Criddle states that in Canada the adults appear during 
the second week in June and may be met with until about July 10. 
Occasionally they may be found feeding on flowers. Doctor Fletcher 
has taken them in Canada on flowers of the tumbling mustard. It 
is unquestionably true that the time of their appearance and the 
length of adult life are both largely governed by climatic influences 
and vary with the season. 
When confined in emergence tubes or other limited places the males 
develop savage instincts and attack each other without mercy 7 using 
their jaws freely to snip off the antenna?, and, in some cases, the legs 
of their rivals. Singularly, very few of the females confined with 
them are thus mutilated. 
OVIPOSITION 
Weather conditions have always been an important factor in con- 
trolling the oviposition of very many of the Hymenoptera, and they 
are of particular importance in the case of the Cephus. These flies 
go into hiding when the day is dark, damp, cool, or windy. Only on 
bright, warm, still days are they to be found busy with the operation 
of placing their eggs. In Utah, where the first studies of their habits 
were made, the mornings and evenings are chilly as a rule, hence the 
activity of these flies is confined to the hours near midday. They 
are everywhere the most active between the hours of 10 a. m. and 
2 p. m. 
The swaying of the grass and grain stems in the wind appears to 
be a hindrance to them in alighting and ovipositing. A gentle breeze 
will often keep them hovering for several minutes to the windward 
of their goal, while a sudden mountain gust is apt to put an abrupt 
end to all efforts for the balance of the day. Their actions are con- 
trolled by unknown factors, for sometimes on a still, sunny day they 
will spend much of the time roosting on the stems, while again, under 
apparently the same conditions, they are constantly in motion, flying 
and hovering a long time before alighting. 
While the female is poised in the air before a sod of grass or grain 
she is evidently busy selecting the particular stem in which she hopes 
to oviposit. Once she has chosen and settled, she seldom changes 
to another stalk, although she may halt at several places on a single 
stem and attempt oviposition at each pause. Occasionally, after a 
hasty examination, she may again take to wing and make another 
choice. Repeated observations seem to have established the fact 
that one of the chief requisites of a proper stem is that it shall not yet 
have put forth a head. In all the countless instances where ovipo- 
sition has been observed, the female has never been known to choose 
a stem with a head. 
