PAKASITES OF NORTHERN ARMY-WORM. 



707 



distiugiiisbable, bas two little flattened plates that were the breathing- 

 pores in the larva. The two first segments are partially split off, and 

 ruptnred across the end, where the fly burst out. The fly appeared the 

 20th of September. 



" The eggs," ^Ir. Walsh says, " are much the shape and color of those 

 of the flesh-fl^'. The fly fastens its eggs by an insoluble cement on the 

 upper surface of the two or three first rings of the body. Instinct ap- 

 pears to teach the mother-fly that if she places her eggs further back, 

 the little maggots, as they hatch out and begin to penetrate the flesh, 

 will be felt by the victim and seized by its powerful jaws, as I have seen 

 wood-feeding caterpillars seize and worry like a dog ants that attacked 

 them." 



Mr. Walsh had fifty or sixty worms, of which all but two had their 

 eggs, from one to six iu number, fastened on their upper side. From 

 these he bred fifty-four Tachinas and two moths. " Xow these army- 

 worms averaged about three eggs apiece, and consequently two-thirds 

 of the eggs of the Tachina must have perished witliout arriving at ma- 

 turity." 



" My Tachina eggs, so far as I noticed, did not hatch till the larva 

 had gone under ground ; but from information received from Mr. Emery, 

 I have reason to believe that, under certain circumstances, this, or an 

 allied species, hatches out above ground, adhering externally, and 'grow- 

 ing rapidly, while its victim decreases in size.' They uniformly devoured 

 the larva before it transformed into the pupa state. The time for the 

 entire transformation of such as I experimented upon from egf^ to fly, 

 was from fifteen to nineteen days." * * * "Jefferson Eussell, an in- 

 telligent farmer, had repeatedly, on damp, cloudy mornings, watched a 

 large, bluish-green fly, about the size of a blow-fly, attacking the army- 

 worm, and depositing its eggs on the shoulders of the victim, as he as- 

 certained by a double lens. As they were attacked, the army-worms 

 kept dropping to the ground and gathering in clusters, or hiding under 

 clods, until finally the wheat on wliich they occurred was entirely free 

 from them." Mr. Eiley says that in 1875 fully 80 per cent, of the army- 

 worms which he noticed were attacked hy the TacJiina Hies. "They 

 never abound or travel from one field to another, but they are accom- 

 panied by a number of two-winged flies, which are often so numerous 

 that their buzzing reminds one of a swarm of bees." — (Eighth Eeport.) 

 This fact supports the opinion of Wagner (see p. ) that insect-para- 

 sites usually increase in proportion to their hosts. 



Eijg. — When first laid, spherical, 0.02 inch in diametei", smooth, opaqne white: cov- 

 ered with a glistening, adhesive lluid; shell delicate, becoming faintly iiridesceut and 

 more soi'did before hatching. — (Riley.) 



Larva. — When first liatohed, 1.7 

 millemeter in length; dull white, 

 and a largo dark head. 



In the first and second stages, 

 the two front pairs of abdominal 

 legs are atrophied so as to necessi- 

 tate a looping gait. In the third 

 stage the looping habit is lost, but 

 the front abdominal legs are still 

 somewhat the smallest. In the Fig. C— Pup.a 

 fourth stage, the color is dull, dark ^F Chrysa- 

 greeu,and thechanieleonitic brown ^^* 

 lines appear. — (Riley.) 

 The mature larva is about an inch and a half long. Its cylindrical body, divided 

 into thirteen rings, becomes more contracted and wrinkled at each end, and is sparsely 

 covered with short hairs. The head is covered by a net-work of confluent spots, while 

 along the middle of the face run two lines diverging at each end. A light-colored Avaved 

 line, just above the legs, is succeeded by a dark one ; then a light one, edged with two 



Fig. .'). — Full-grown Northern Armj-worm. 



