384 INSECTS INJURIOUS TO VEGETATION. 



the rain-bow, and have a smoky tinge, forming a cloud or broad 

 band across the middle of the first pair ; the veins are brownish. 

 The body of the female measures rather more than one fifth of 

 an inch in length ; that of the male is smaller. In the year 1828, 

 I observed these saw-flies, on cherry and plum trees, in Milton, 

 on the tenth of May ; but they usually appear towards the end 

 of May or early in June. Soon afterwards some of them begin 

 to lay their eggs, and all of them finish this business and disappear 

 within the space of three weeks. Their eggs are placed, singly, 

 within little semicircular incisions through the skin of the leaf, 

 and generally on the lower side of it. The flies have not the 

 timidity of many other insects, and are not easily disturbed while 

 laying their eggs. On the fourteenth day afterwards, the eggs be- 

 gin to hatch, and the young slug-worms continue to come forth 

 from the fifth of June to the twentieth of July, according as the 

 flies have appeared early or late in the spring. At first the slugs 

 are white ; but a slimy matter soon oozes out of their skin and 

 covers their backs with an olive-colored sticky coat. They have 

 twenty very short legs, or a pair under each segment of the body 

 except the fourth and the last. The largest slugs are about nine 

 twentieths of an inch in length, when fully grown. The head, of 

 a dark chestnut color, is small, and is entirely concealed under 

 the forepart of the body. They are largest before, and taper 

 behind, and in form somewhat resemble minute tadpoles. They 

 have the faculty of swelling out the forepart of the body, and 

 generally rest with the tail a little turned up. These disgusting 

 slugs live mostly on the upper side of the leaves of the pear and 

 cherry trees, and eat away the substance thereof, leaving only the 

 veins and the skin beneath untouched. Sometimes twenty or 

 thirty of them may be seen on a single leaf ; and, in the year 

 1797, they were so abundant, in some parts of Massachusetts, 

 that small trees were covered with them^ and the foliage entirely 

 destroyed ; and even the air, by passing through the trees, be- 

 came charged with a very disagreeable and sickening odor, given 

 out by these slimy creatures. The trees attacked by them are 

 forced to throw out new leaves, during the heat of the summer,- 

 at the ends of the twigs and branches that still remain alive ; and 

 this unseasonable foliage, which should not have appeared till the 



