RAVAGES OF THE ARMORED SCALES. 45 



sufficient to sustain tlio weight of Hie little aeronaut, or until in its sweep 

 it becomes entangled in the branches oi' a distant tree or shrub, and 

 forms a bridge upon which the spider readily crosses. 



The warm ascending currents of spring, the southeast trade-winds 

 in Florida, excite multitudes of spiders to set out upon their travels, 

 speeding them on their way and directing their course. At this season 

 of the year, when the migrations of insects are at their height, and all 

 nature is in restless activity, Scale-insects also are most abundantly pro- 

 ductive, and the leaves and branches of infested trees swarm with their 

 young. Thus it is that in spring especially the spiders, aided by the 

 winds, carry the Bark-lice in numbers and to great distance-. 



Conditions favorable to their Increase. There is good reason to believe 

 that Bark-lice, like many other destructive insects, do not, as a rule, 

 originate the disorders which follow their attacks. An enfeebled con- 

 dition of the plant, from whatsoever cause it arises, is generally neces- 

 sary to provoke an invasion. Thoroughly healthy trees, even when in- 

 fected, may remain uninjured for years. The Scale insects upon them 

 thrive only upon the lower or inside branches, and are held in check by 

 their natural enemies and parasites. An unfavorable atmospheric con- 

 dition, such as long-continued drought, the impoverishment of the soil, 

 neglect of cultivation, and the many obscure or utterly unknown causes 

 which produce u die-back, 7 ' yellow and streaked foliage, or other indi- 

 cations of vegetable indigestion, if such it may be called, all tend to 

 foster Scale-insects and favor their rapid increase. 



In explanation of these facts, it may be conjectured, although it is 

 not, perhaps, susceptible, of proof, that peculiar conditions of the sap 

 are especially favorable to the development of Scale-insects, and affect 

 the reproductive functions, stimulating the females to greater produc- 

 tiveness. Observations show that the number of eggs deposited varies 

 considerably, and that the maximum number is produced, not by soli- 

 tary females upon vigorous p'ants, .but by individuals of the advancing 

 I. rood taken from portions of the plant plainly affected by their attacks. 



Usual course of the Pest. If it be true that outbursts of Scale-insects 

 commonly owe their origin to some disturbance in the condition of the 

 plant, it is no less a lict that their ravages not only aggravate the 

 original trouble, but entail others, it may be, far more s>jrioas in their 

 consequences. The countless throng of Bark-lice not only weaken the 

 plant by sapping and diverting its \italjuices and depriving it of nour- 

 ishment, but they also strangle the parts which they infest by coating 

 the surface and c'ogging its pores with their myriad bodies. Their 

 long, hair like sucking beaks penetrate and thread the cellular tissues 

 of the growing bark, breaking through and altering its structure so 

 that the tender bark of the twigs and younger shoots is destroyed, 

 while the thicker bark of the trunk and larger limbs hardens and be- 

 comes, as it is popularly termed, u hide-bound." 



In this condition healthy growth is impossible. If neglected and al 

 lowed to be overrun by the pest, the growth of the treo is checked; 



