380 INSECTS OF MASSACHUSETTS. 



regularity in the plan of the Creator. In considering the resem- 

 blances of species, we cannot fail to admire the care that has 

 been taken, by almost insensible shades of difference among 

 them, or by peculiar circumstances controlling their distribution, 

 their habits of life, and their choice of food, to prevent them 

 from commingling, whereby each species is made to preserve for 

 ever its individual identity. 



The saw-fly of the rose, which, as it does not seem to have 

 been described before, may be called Selandria Rosa, from its 

 favorite plant, so nearly resembles the slug-worm saw-fly as not 

 to be distinguished therefrom except by a practised observer. It 

 is also very much like Selandria barda, Vitis, and pygmcca, but 

 has not the red thorax of these three closely allied species. It is 

 of a deep and shining black color. The first two pairs of legs 

 are brownish gray or dirty white, except the thighs, which are 

 almost entirely black. The hind-legs are black, with whitish 

 knees. The wings are smoky, and transparent, with dark brown 

 veins, and a brown spot near the middle of the edge of the first 

 pair. The body of the male is a little more than three twentieths 

 ctf an inch long, that of the female one fifth of an inch or more, 

 and the wings expand nearly or quite two fifths of an inch. 

 These saw-flies come out of the ground, at various times, be- 

 tween the twentieth of May and the middle of June, during which 

 period they pair and lay their eggs. The females do not fly much, 

 and may be seen, during most of the day, resting on the leaves ; 

 and, when touched, they draw up their legs, and fall to the ground. 

 The males are more active, fly from one rose-bush to another, 

 and hover around their sluggish partners. The latter, when about 

 to lay their eggs, turn a little on one side, unsheathe their saws, 

 and thrust them obliquely into the skin of the leaf, depositing, in 

 each incision thus made, a single egg. The young begin to hatch 

 in ten days or a fortnight after the eggs are laid. They may 

 sometimes be found on the leaves as early as the first of June, 

 but do not usually appear in considerable numbers till the twen- 

 tieth of the same month. How long they are in coming to ma- 

 turity, I have not particularly observed ; but the period of their 

 existence in the caterpillar state probably does not exceed three 

 weeks. They somewhat resemble the young of the saw-fly in 



