6 4 



ENTOMOLOGY 



Glandular Hairs and Spines. The presence of adhesive hairs on 

 the empodium of the foot of a fly enables the insect to walk on a smooth 

 surface and to walk upside down; these tenent hairs emit a transparent 

 sticky fluid through minute pore canals in their apices. The tenent 

 hairs of Hylobius (Fig. 98) are each supplied with a flask-shaped unicellu- 

 lar gland, the glutinous secretion of which issues from the bulbous ex- 

 tremity of the hair. Bulbous tenent hairs occur also on the tarsi of Col- 

 lembola, Aphididae and other insects. 



Nettling hairs or spines clothe the caterpillars of certain Saturniidae 

 (Automeris), Liparidae, etc. These spines (Fig. 99), which are sharp, 

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

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



FIG. 98. Section across tarsus of a beetle, 

 Hylobius, to show bulbous glandular hairs. 



After SlMMERMACHER. 



P'iG. 99. Stinging hair of a caterpillar, 

 Gastro pacha, c, cuticula; g, gland cell; h, 

 hair; hy, hypodermis. After CLAUS. 



Lagoa crispata (Fig. 100) 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 defence against birds and other in- 

 sectivorous vertebrates as well as against predaceous insects. The blood 

 itself serves as a repellent fluid in the oil-beetles (Meloidae) and Coccinel- 

 lidas, 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 sub- 

 stance, which is an almost perfect protection against birds, reptiles and 

 predaceous insects. Coccinellidae and Lampyridae are similarly exempt 



