PARASITES OF ANIMALS. 9 



insects properly called bugs, such as the squash-bug (figure 

 13), strawberry-bug, bed-bug, and also the cicada or "seven- 



Fig. 12, 



Fis. 13 



tccn-year locust," the plant-lice, bark-lice, cuckoo-spits, the 

 true lice, bird-lice, etc. In tliis order we find, therefore, the 

 greatest number of external parasites; The wings, when 

 present, are often crossed upon the back, and the front wings 

 are often thickened toward the base, but in other cases, as in 

 the cicada and plant-lice, the wings are transparent and not 

 crossed. The mouth organs form a sharp hollow proboscis, 

 for piercing the bark of plants or skin of animals, in order to 

 suck up the blood or sap. When not in use the proboscis can 

 be folded down upon the breast, by means of three joints. 

 The mandibles and maxillae are four, long, slender, very 

 sharp, piercing organs, often barbed near the points. These 

 are enclosed in the jointed proboscis, as in a sheath, but can 

 be thrust out through the opening in the end. The proboscis 

 is formed mostly by the lower lip or labium, but the opening 

 in the upper side is covered by the shorter upper lip. The 

 larvae of many Hemiptera resemble the adults from the first, 

 except that they lack wings ; the pupae are also active and 

 have the same habits. They therefore undergo less remark- 

 able transformations than those of the preceding orders.. 

 Many of these insects are beneficial by destroying other in- 

 sects, but most are injurious to vegetation by sucking sap. 



Figure 12. — Ap]^le-tree Borer (Saperda Candida Fabr.), natural size. Color 

 light brown with two white stripes ; the lower figure represents the larvae. From 

 Packard's Guide. 



Figure 13. — Squash-bug (Cm-eus trtstts DeGeer.), natural size. Color dark, 

 brown. From Packard's Guide. 



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