10 
THE ESSEX NATURALIST. 
was also desirable, he said, to record the direction of rotation of the air 
column. This could usually be determined after the passage of the storm 
by noting the way in which trees had fallen. 
HORNETS, WASPS, AND FLIES SUCKING THE 
SAP OF TREES. 
By MILLER CHRISTY, F.L.S. 
[Read 30 th November 1918]. 
B ESIDE the drive leading up to my house, there are-a 
number of fine old elms (a dozen or twenty of them 
altogether), which have been identified recently by Prof. M. 
Henry as Ulmus glabra Miller. That they are really large and 
ancient—past their prime, indeed—may be gathered from 
the fact that they have in them numerous holes which form 
the nesting-places of many birds, including White Owls, Little 
Owls, Kestrels, Stockdoves, Jackdaws, Starlings, and Sparrows. 
For several years past, I have noticed that, every autumn, 
from about the middle of August to the middle of September (in 
short, during the ordinary wasp season), the bark on the stem 
of a particular one of these trees is infested by hornets, wasps, 
and many kinds of flies. The two former crowd into the deeper 
cracks in the bark, especially at certain spots. At these spots, 
groups of three or four hornets or a dozen Wasps (but never 
the two mixed) may frequently be seen, all having their heads 
inwards and their tails outwards, and all apparently sucking 
or gnawing hard at the deepest part of the crack. The flies, 
on the other hand, appear seldom or never to enter the cracks, 
but stand around on the surface of the bark at a respectful 
distance from their deadly enemies the wasps. The wasps, 
in their turn, also keep to themselves, never mixing with the 
hornets, of which they appear to be in fear. No doubt they 
have good reason ; for our member, Mr Henry Mothersole, 
coming up the drive one afternoon and stopping a moment 
to uTitch the assembly, sau^ a hornet seize three u'asps, one 
after the other, in quick succession, biting and killing each 
in turn, and then throwing the body aw^ay, as if in contempt. 
This habit of theirs accounts largely, no doubt, for the fact 
that the ground immediately around the base of the tree is 
