EXPERIMENT STATION BULLETINS. 397 



mon on our own celery, but it was the late brood, and although it nearly 

 stripped the leaves in some places, the work came so late that the celery 

 was nearly ready for market and had completed its growth. Parasites so 

 thinned the numbers of the caterpillar last fall and early this summer that 

 this season only a few appeared. The caterpillars feed only on the leaves, 

 remaining in a group while young, but soon separate and feed by 

 themselves. 



LIFE HISTORY. 



The eggs (see A, Fig, 15) are placed by the moth in a little group on the 

 under side of the outer leaves, often near one edge. She is very prolific, 

 laying in a compact bunch usually from 125 to 150 eggs, but in one 

 instance this season a cluster of 452 eggs was counted. In from two to 

 three weeks the eggs hatch into little hairy, speckled, white caterpillars 

 with a black head and black crescent on the thorax. While in this condi- 

 tion they feed in a group and will suspend themselves by a web when dis- 

 turbed. Their life in this attire lasts only two or three days when they don 

 a bright new coat entirely different from the former one. The covering 

 now is of much the same color that it is in the mature form. The head and 

 legs are a reddish yellow and the rest of the body black except the two 

 stripes, one bluish white and the other light yellow, connected by irregu- 

 lar cross lines. The caterpillars pass through several more moults as they 

 grow. At maturity they measure nearly two inches in length. They then 

 go into the ground where they pupate and after they remain in this rest- 

 ing stage for a short time, appear as moths. 



There are two broods each year, the first one coming in June and July 

 and the second appearing in September. This last brood is hardly half 

 grown when it leaves the celery for winter quarters in some protected 

 place and comes forth early in the spring to complete its growth. 



PARASITES. 



The second brood last fall were largely parasitized by a small four- 

 winged fly {Microplitis mamestrcB Weed), bred from the zebra caterpillar 

 and described several years ago by Dr. Weed. We have no access to his 

 papers on this parasite, but perhaps a few notes from what was observed 

 by myself will show the method of its work to those not familiar with the 

 ways of parasites. By the time the caterpillar is nearly half grown the 

 parasite inside the caterpillar is full grown. It then issues from the side 

 of the caterpillar only a short distance in front of the last pair of legs. 

 When only part way out it begins spinning its silky threads and attaching 

 them firmly to the caterpillar around it. From this foundation it weaves out 

 by looping the web outward nearly an eighth of an inch and fastening each 

 time as it is brought back. After a little basket is formed in this way on 

 one side, the parasite issues entirely and enters the web sack it has made. 

 The next thing is to stretch and shape the sack, strengthening it all the 

 while in the weak places. Then begins the gradual closing of the embryo 

 cocoon around the parasite, finishing last on one side next the caterpillar, 

 but before entirely enclosed it fastens webs that draw it tight to the side 

 or else under the caterpillar. The work so far has taken the parasite 

 about three quarters of an hour. The rest of the work is a series of weav- 

 ing, turning, pushing, and shaping till it has made the web so thick in two 

 or three hours that it can no longer be seen. The cocoon is about one 



