250 INSECT LIFE 



XVIII 



the entrance, cannot see her enemy audaciously 

 perched on the hind quarters of the prey, or, if she 

 suspects the bandit's presence, cannot drive it away, 

 having no freedom of movement in the strait 

 passage, and in spite of all precautions to facilitate 

 speedy entrance, cannot always vanish underground 

 with the celerity required, so quick is the parasite. 

 In fact, this is the only propitious moment, since 

 prudence forbids the Dipteron to penetrate into the 

 den, where other Diptera, far stronger than itself, are 

 served up as food for the larvae. Outside, in the 

 open air, the difficulty is insurmountable, so great 

 is the vigilance of the Bembex. Let us give a 

 moment to the arrival of the mother, when the nest 

 is being watched by the Miltogramma. 



Some of these flies — more or fewer, generally 

 three or four — have settled on the sand and are 

 quite motionless, all gazing at the burrow, the 

 entrance of which they know very well, carefully 

 hid though it be. Their dull -brown colour, their 

 large crimson-red eyes, their intense stillness, have 

 often made me think of bandits who, dressed in a 

 dark material, with a red kerchief over their heads, 

 are lying in wait to do some evil deed. The 

 Hymenopteron comes, loaded with prey. Had she no 

 anxieties she would alight straightway at her door. 

 Instead, she hovers at a certain height, descends 

 slowly and circumspectly, hesitates, and vibrates her 

 wings, producing a plaintive hum denoting appre- 

 hension. She must have seen the malefactors. 

 They too have seen the Bembex. The movement 

 of their red heads shows that they are following her 

 with their eyes ; every gaze is fixed on the coveted 



