ANATOMY AND PHYSIOLOGY 



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extremity of the hair. Bulbous tenent hairs occur also on the tarsi of 

 Collembola, Aphididae and other insects. 



Nettling hairs or spines clothe the caterpillars of certain Saturniidae 

 (Automeris), Liparidae, etc. These spines (Fig. 101), which are sharp, 

 rittle and filled with poison, break to pieces when the insect is handled 

 and cause a cutaneous irritation much like that made by nettles. In 

 Lagoa crispata (Fig. 102) the irritating fluid is secreted, as* is usual, by 

 several large hypodermal cells at the base of each spine. These irritating 

 hairs protect their possessors from almost all birds except cuckoos. 



Repellent Glands. The various offensive fluids emitted by insects 

 are also a highly effective means of defense against birds and other in- 

 sectivorous vertebrates as well as against predace- 

 ous insects. The blood itself serves as a repellent 

 fluid in the oil-beetles (Meloidae) and Coccinellidae, 

 issuing as a yellow fluid from a pore at the end of 

 the femur. The blood of Meloidae (one species of 

 which is still used medicinally under the name of 

 "Spanish Fly") contains cantharidine, an extremely 

 caustic substance, which is an almost perfect pro- 

 tection against birds, reptiles and predaceous insects. 

 Coccinellidae and Lampyridae are similarly exempt from 

 attack. Larvae of Cimbex when disturbed squirt 

 jets of a watery fluid from glands opening above the 

 spiracles. Many Carabidae eject a pungent and often 

 corrosive fluid from a pair of anal glands (Fig. After PACKARD. 

 148); this fluid in Brachinus, and occasionally 

 in Galerita janus and a few other carabids, volatilizes explosively 

 upon contact with the air. When one. of these "bombardier-beetles" 

 is molested it discharges a puff of vapor, accompanied by a distinct 

 report, reminding one of a miniature cannon, and this performance 

 may be repeated several times in rapid succession; the vapor is acid and 

 corrosive, staining the human skin a rust-red color. Individuals of a 

 large South American Brachinus when seized "immediately began to 

 play off their artillery, burning and staining the flesh to such a degree 

 that only a few specimens could be captured with the naked hand, 

 leaving a mark which remained for a considerable time." (Westwood.) 

 As malodorous insects, Hemiptera are notorious, though not a few 

 hemipterous odors are (apart from their associations) rather agreeable 

 to the human olfactory sense. Commonly the odor is due to a fluid 

 from a mesothoracic gland or glands, opening between the hind coxae. 



FIG. 102. sting- 



