MAPLE LEAF-MINERS. 411 
52. The ocellate leaf gall of the red maple. 
Sciara ocellaris Osteu Sacken. 
Order Diptera ; family Mycetophilid^e. 
(Plate xxxviii.) 
On the leaves of the red maple (Acer rubrum) circular ocellate spots about three- 
eighths inch in diameter, with disk yellow, and margin and central dot, during one 
stage of their growth, cherry-red. 
The following account of this fly is taken entire from Professor Com- 
stock's report as U. S. Entomologist for 1881 : 
The foliage of the red maple (Acer rubrum) is often seriously injured by certain very 
small larvae, which make large and conspicuous spots or galls upon it. This insect 
is apparently widely distributed. I have observed it both at Washington and at 
Ithaca, N. Y. In the last-named place it occurs so abundantly that I have repeatedly 
seen trees every leaf of which was infested. 
This insect is so small that of itself it would not readily attract attention, but the 
result of its work is so conspicuous that it may be seen from a long distance. This 
appears in the form of a circular spot, three-tenths to three-eighths inch in diameter, 
which at a certain period of its growth is light yellow in color, with a cherry-red 
margin and central dot. (See pi. xxxviii, fig. 1.) At other periods the spot is simply 
light green or yellow. Frequently these spots occur so thickly as to intersect each 
other and to completely cover the leaf, fifty or more being on a single leaf. At the 
center of each spot may be seen, on the other side of the leaf, an elevated portion. 
Corresponding to this, on the lower surface of the leaf, there is a pit, within which 
the larva lives. Larvae that were partially grown were found to be held in place in 
the pit in the leaf by what appeared to be a larval skin. This pellicle covers the 
body entirely, and is with difficulty removed from it ; the edges of the pellicle adhere 
quite tightly to the leaf. Where the larva is full grown it forces itself from under 
this skin, which then falls back into the cavity, or is pushed to one side, where fre- 
quently it may be seen adhering to the leaf. The larva at this time drops to the 
ground, into which it enters to undergo its transformation. 
The larvae are translucent, viscid, nearly colorless. Those m the galls are broad 
oval (see pi. xxxviii, fig. 3) ; but those which have left them are more elongated, taper- 
ing almost equally towards each end. On the lateral margin of each abdominal seg- 
ment there are one or more short spines, which are directed towards the caudal end 
of the body ; and on the dorsal surface of each abdominal segment, near each lateral 
margin, there is a small tubular spiracle. There is a distinct head (see pi. xxxviii, 
fig. 3a), which bears short but conspicuous antennae. The caudal end of the body 
(see pi. xxxviii, fig. 36) bears a pair of fleshy appendages, each of which is furnished 
with a pair of spines similar to those on the margin of the segment, and a large 
number of triangular teeth. 
The larva spins something like a cocoon a short distance below the surface of the 
ground. To this cocoon the particles of sand firmly adhere so that it can be distin- 
guished from the soil only with difficulty. The pupa is yellowish white, with large 
black eyes. When the pupa is about to transform to an adult it emerges for about 
two-thirds of its length from the cocoon. The pupa skin remains firmly attached in 
this position. (See pi. xxxviii, fig. 4.) 
From larvae collected at Washington May 15, the adult emerged from June 14 to 
June 16. I have not yet sufficient data to determine the number of generations each 
year; but I believe there are several. Larvae were observed at Ithaca during the 
latter part of September ; they went into the ground September 26. 
