51 



much like the curculio does, and remain for a short time motionless ; their structure, how- 

 ever, is not such as will permit of their disguising themselves as thoroughly as the " little 

 turk " Joes, and hence they are easily detected. During the past season these flies were very 

 numerous during the early part of June, and their progeny was destructive in a correspond- 

 ing degree later in the summer. 



After pairing the female places her eggs singly within little semicircular incisions through 

 the skin of the leaf, which is frequently followed by some discolouration at the point of inser- 

 tion. Harris says that the eggs are generally placed on the lower side of the leaves, whereas 

 in our experience we have found them quite as often on the upper side. According to the 

 same author the flies all finish this business of egg depositing and disappear within the space 

 of three weeks. " The flies have not the timidity of many other insects, and are not easily dis- 

 turbed while laying their eggs. On the fourteenth day afterwards the eggs begin to hatch, and 

 the young slug worms (see those on leaf in Fig. 41) continue to come forth from the fifth of 

 June to the 20th of July, according as the flies have appeared early or late in the spring." 

 Fig- ^1- " At first the slugs are white; but a slimy 



"""^ matter soon oozes out of their skin, and covers 



their backs with an olive-coloured sticky coat. They 

 have twenty very short legs, or a pair under each 

 segment of the budy excepting the fourth and the 

 last. When fully grown (See n Fig. 41) they are 

 _ about nine-twentieths of an inch in length. The 



head which is of a dark chestnut colour is small,and is entirely concealed under the fore part of 

 the body. They are largest before, and taper behiud, and in form somewhat resemble minute 

 tadpciles. They have the faculty of swelling out the fore part 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, became charged with a very disagreeable and sickening odour, 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, and this unseasonable 

 foliage which .should not have appeared until the next spring, exhausts the vigour of the trees, 

 and cuts off the prospect of fruit." 



" The slug worms come to their growth in twenty-sis days, during which period thoy 

 cast their skins five times. Frequently as soon as the skin is shed, they are seen feeding 

 upon it ; but they never touch the last coat which remains stretched out upon the leaf. After 

 this is cast off, they no longer retain their slimy appearance and olive colour, but have a clean 

 yellow skin, entirely free from vicidity. They change also in form and become proportion- 

 ally longer, and their head and the marks between the rings are plainly to be seen. In a few 

 hours after this change they leave the trees, and, having crept or fallen to the ground, they 

 burrow to the depth of from one inch to three or four inches, according to the nature of the 

 soil. I'y moving their body the earth around them becomes pressed equally on all sides, and 

 an oblong, oval cavity is thus formed, and is afterwards lined with a sticky glossy substance, 

 to which the grains of earth closely adhere. Within these little earthen cells or cocoons the 

 change to ihrysalids takes place, and in sixteen days after the descent of the slug worms, finish 

 their transformations, break open their cells, and crawl to the surface of the ground, where 

 they appear in the fly form. These flies usually come forth between the middle of July and 

 the 1st of August, and lay their eggs for a second brood of slug-worms. 'J'he latter come to 

 their growth and go into the ground in September and October, and remain there till the fol- 

 lowing spring, when they are changed to flies and leave their winter ((uarters. It seems that 

 all of them, however, do not finish their transformation at this time ; some are found to re- 

 mam unchanged in the ground till the following year ; so that if all the slugs of the first hatch 

 in any one year should happen to be destroyed, enough from a former brood would still re- 

 main in the earth to continue the .species.'' 



" The disgusting appearance and smell of these slug-worms do not protect them (rom the 

 attacks of various enemies. Mice and other burrowing animals destroy many of them in 

 their cocoons, and it is probable that birds also prey upon them whca on the trees both in the 



