83 
for the purpose of forming pockets or receptacles for the eggs. 
These eggs have the peculiar property of swelling when they 
come in contact with the sap, and are thus securely kept in 
position inside the small pockets made by the saws. 
The larve or false-caterpillars of these insects often cause 
great damage by devouring the foliage of our shrubs, shade 
and fruit-trees, nor does the grain and small fruit escape. The 
willows and poplars used as wind breaks are their favorite 
food-plants in Minnesota, and here they multiply to such an 
extent as to very seriously injure the trees. 
CURRANT INSECTS. 
THE IMPORTED CURRANT-WORM. 
(Nematus ventricosus Klug. ) 
The most destructive insect that attacks the currant is the 
above named saw-fly which feeds indiscriminately upon all 
kinds of currants and gooseberries. <A second species, anative 
of the United States, is only occasionally found in Minnesota, 
mainly upon the wild species of the above named plants; but 
only in extreme cases does it become numerous enough to cause 
damage. ‘The imported species is supposed to have been acci- 
dentally introduced into this country about the year 1857, and 
has since spread over the greater part of the United States and 
Canada, The eggs are glued to the main-ribs of the leaf as 
shown in Fig. 41, and not inserted into pockets as is usually 
the case with saw-flies. This insect furnishes an excellent 
illustration of the rather general rule that an organ not used, 
soon becomes rudimentary. Like all saw-flies, the female of 
this insect possesses a pair of saws, but these consist simply 
of the blades,and are minus the real teeth, which are reduced to 
mere dull projections. In from four to ten days, the egg 
hatches into a very small whitish caterpillar with a white head 
ornamented with black spots on each side. This color, how- 
ever, changes to green as soon as the caterpillars begin to 
feed, and after their first skin is shed, the head becomes black 
and many black spots appear on the body. This coloration 
persists until.the last molt when the insect becomes grass- 
green. The head, however, retains the black spots on each 
side. The length of the worm is now about three-fourths of an 
