THE INSECT ASSOCIATION OF A LOCAL ENVIRONMENTAL COMPLEX. 
45 
effect in this way is negligible. Many insects are anemotropic, and in moderate 
breezes will orient themselves head-on to the air-current, maintaining a seemingly 
motionless attitude on the wing for quite appreciable periods. Species of Bibio will 
often be observed maintaining their bodies headed to a gentle breeze, changing their 
position to the windward as the breeze veers in one direction or another. Many 
Anthomyiidse, Syrphidse, and Ghironomidae have a similar behaviour, and Folsom * 
quotes Wheeler as having observed Empidx swarming in one spot every day for no 
less than two weeks, probably on account of some particular odour emanating from 
the ground which attracts and arrests the flies as they emerge from their pupse. In 
this latter case, perhaps chemotropism determines their curious behaviour as much 
as anemotropism. 
Many insects are undoubtedly carried before the wind from one association to 
another, and it may be of decided importance in migration and invasion. Other- 
wise it would often be difficult to explain why certain insects which belong to wood- 
land associations are sometimes met with in grassland. During violent dis- 
turbances of the atmosphere winged insects generally seek shelter near the ground 
amongst the herbage. 
The readings for the temperature, pressure, and rainfall were made each day 
at 9 a.m. Standard instruments were used. For accurate results in the study of 
biological phenomena, however, it is recognised that self-recording apparatus is 
essential, whereby the actual temperature fluctuations throughout the course of 
the day are obtained. The monthly averages of the soil-temperature records at 
Holmes Chapel show, a seeming discrepancy, in that apparently the temperature 
at a depth of six inches at no time, during the fifteen months covering the in- 
vestigation, rose above that at the depth of eighteen. This is, of course, erroneous, 
and due to the fact that the readings were made at a time (9 a.m.) when the soil 
at the uppermost layer of six inches has lost most of its heat during the night by 
radiation to the layers beneath and to the atmosphere, whilst the effect of the 
sun’s rays have not yet reached sufficient strength to warm it up. In the summer 
months at midday, in bright warm weather, the surface layer is generally a few 
degrees warmer than the layers immediately beneath. In the winter months, during 
periods of frost and snow, the converse prevails. 
The earlier months of 1914 were milder than those of 1913 , as a glance at 
Table XII will show at once. Whereas, in January 1913 , the average maximum 
air temperature was 42 ° F., in January 1914 it was as high as 58 ° F. ; the average 
maximum for the same month of 1914 was 37 ° F. compared with 31 ° F. for the 
corresponding month of the previous year ; the average minimum temperature on 
grass differed by 4 ° F., 31 ° F. in January 1913 and 35 ° F. in January 1914 . The 
average soil temperatures for these same months also varied ; at six inches depth, 
January 1913 , 40 ° F., January 1914 , 38 ° F., a drop of 2 ° F. ; at eighteen inches below 
* Folsom, J. W., Entomology : its Biological and Economic Aspects, Philadelphia, 1906, p. 348. 
TRANS. ROY. SOC. EDIN., VOL. L1I, PART I (NO. 2). 
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