2-1 



Chapter II. 



STRUCTURES FOR PROTECTING EGOS. — MASON-WASPS ; 

 MASON-BEES ; MINING-BEES. 



The provisions which are made by the different 

 species of insects for protecting their eggs, appear in 

 many cases to be admirably proportioned to the kind 

 of danger and destruction to which they may be ex- 

 posed. The eggs themselves, indeed, are not so liable 

 to depredation and injury as the young brood hatched 

 from them ; for, like the seeds of plants, they are ca- 

 pable of withstanding greater degrees both of heat and 

 cold than the insects which produce them. According 

 to the experiments of Spallanzani, the eggs of frogs 

 that had been exposed to various degrees of artificial 

 heat were scarcely altered in their productive powers 

 by a temperature of 111 of Fahrenheit, but they 

 became corrupted after 133°. He tried the same ex- 

 periment upon tadpoles and frogs, and found they 

 all died at 111°. Silk- worms died at a temperature 

 of 108°, while their eggs did not entirely cease to be 

 fertile till 144°. The larvae of flesh-flies perished, 

 while the eggs of the same species continued fertile, 

 at about the same comparative degrees of heat as in 

 the preceding instances. Tntense cold has a still less 

 effect upon eggs than extreme heat. Spallanzani ex- 

 posed the eggs of silk-worms to an artificial cold 23 

 below zero, and yet, in the subsequent spring, they 

 all produced caterpillars. Insects almost invariably 

 die at the temperature of 14°, that is at 16° below the 

 freezing point*. The care of insects for the pro- 



• See Spallanzani's Tracts, l>y Halyell, vol. i. 



