It is quite common for
the upper surface of the leaves of certain maple trees,
primarily silver maple (Acer
saccharinum) and red maple (Acer
rubrum) but sugar maples (Acer
saccharum) are less bothered, to be covered with
small, reddish, round wart-like structures about 1/16 to
1/8 inch in diameter. They tend to appear by mid-May and
are green at first. Eventually, they turn a reddish
color.
The smaller type of gall
are called bladder galls and are caused by
spider mites of the
species, Vasates quadripedes. Taller, upright
growths called spindle galls are the result of damage by
the mites in the species, Vasates aceriscrumena.
The mites over winter as
adults and feed on the developing leaf buds in the early
spring. This feeding results in the development of the
galls which are somewhat equivalent to tumors in
animals.