SOME PLANT GALLS 
AND HOW THEY COME 
E. P. FELT 
New York State Entomologist 
An Obscure Group of Insects Causing Plant Warts that are Frequently Laid to Attacks of Fungus 
O UR 10 S 1 TY is always excited by the unusual, and the 
appearance of an abnormal growth upon some plant 
in the garden never fails to arrest interest and occasion- 
WMM ally may cause apprehension for the plant’s welfare. 
In some instances such a growth may seriously mar the appear¬ 
ance of the affected plant or, in extreme cases, even bring about 
the death of large trees. Many of these unusual appearances 
on plants are produced by insects and are known as “galls.” 
The gall is the plant’s response to a certain stimulus produced 
by the puncture of the insect and is always the same for the 
given insect on that particular species of plant. 
A somewhat common gall is the delicate, creamy-white, pink- 
spotted, woolv, globular growth about an inch in diameter on 
Oak twigs. This appears to be a modification of a series of 
buds which normally develop leaves and branches and in this 
case have been compelled to provide suitable shelter for hun¬ 
dreds of minute, blackish gall wasps. 
The oak bullet galls have such a characteristic appearance 
that descriptions are unnecessary. I here are 
a number of different kinds occurring upon 
various Oaks, and although they are frequently 
abundant, they do not appear to be particularly 
injurious. 
An insect related to this produces the un¬ 
sightly gouty oak twig gall which may be 
one to one and a quarter inches in diame¬ 
ter. They occur upon the smaller branches 
and occasionally are so numerous as to form 
irregular masses several inches long. This gall wasp is very 
local, its attack frequently being confined to one or two trees; and 
in case of severe infestations, branches, good sized limbs, and 
even considerable proportions of large trees may succumb to the 
gradual weakening produced bv the serious interruption in the 
circulation of the sap caused by these abnormal developments. 
Another very similiar gall known as the horned oak gall oc¬ 
curs rather commonly upon certain Southern Oaks. The gall 
itself is more nearly globular. It has a diameter of an inch or 
more and is easily recognized by the tapering, horn-like projec¬ 
tions nearly half an inch long protruding from the surface of the 
deformity. This gall as well as the preceding is sometimes so 
exceedingly abundant as to affect the vitality of branches or 
kill considerable parts of trees. 
Occasionally one may find peculiar kernel-like growths some 
quarter of an inch long and issuing in closely crowded masses 
from longitudinal cracks in the bark of the smaller Oak twigs. 
Infestations by this gall wasp are occasionally very abundant 
and are noteworthy because the galls excrete 
in early summer a sweetish matter very at¬ 
tractive to bees and flies, consequently one’s 
attention to a badly infested tree may be 
drawn by the swarms of insects hovering over 
or flying around the affected branches in 
much the same way as they would if an attrac¬ 
tive plant were in full blossom. 
These twig making gall wasps are unusually 
interesting since they present a peculiar 
AN UNDESIRABLE TRIO 
The badly deformed twigs shown 
above are afflicted with gouty 
oak galls and, being unable to 
develop normally, such un¬ 
fortunates usually die within a 
few years. Another peculiar 
growth occuring upon Oak twigs 
is the banded oak bullet gall 
(left). The Cypress sometimes 
suffers from galls that cause 
the branchlets to swell enor¬ 
mously (right) making healthy 
growth beyond the portions so 
attacked impossible 
354 
