10 THE DENIZENS OF AN OLD CHERRY TREE. 



for December, 1893, he records the bred specimens above, the 

 pupae of which were found in April in burrows of Pemphi-edon 

 lugubrts, the flies, of both sexes, emerging during April and May. 

 In each case, the pupa of FI. /estiva was found close to the aphi- 

 dal remains of the Femphredon larder, and in two instances a 

 pupa was adjacent to a pupal case of Omalus^ showing the 

 parasitical dipteron connected in its economy with the parasitic 

 hymenopteron. From the same burrows of Pemphredon, during 

 April and May, appeared three specimens of Lonchcea vaginalis^ 

 the last bred dipteron of our list. 



We now come to the four remaining fossorial hymenoptera of 

 our cherry stump, all species of the extensive genus Crabro, whose 

 predaceous members provision their nests with Diptera. This 

 genus may always be determined by the constant neuration of the 

 wing (see Fig. 8, PL II.). The species have been tabulated by 

 Mr. Edward Saunders in The Transactio)is of the Entomological 

 Society^ 1880, pp. 280-281 ; also in his chief work on The 

 Hymenoptera Aciileata of the British Isles^ now being issued. 

 Fig. I, PI. I., shows a male of Crabro leucostofnus, a black shining 

 insect, and also four of the tough, sepia-coloured cocoons spun by 

 its larvae, from one of which the Crabro has emerged ; these are 

 all drawn natural size. The female is larger than the male, and, 

 from more than forty cocoons observed in our boxes, only seven per- 

 fect imagines appeared daring May, all of which were males. In the 

 burrow, each cocoon is in the position previously occupied by the 

 stores of the larder, some of the remains of which are usually seen 

 attached to one end of it, consisting chiefly of the harder portions 

 of the pretty green, metallic-looking dipteron, Microchrysa polita^ 

 sometimes mixed with fragments of a brown and yellow species 

 of Melanostoma^ probably M. mellinum, a genus of the family 

 Syrphidcs. As this species was in the pupal stage when the cherry 

 wood was first examined in April, we did not find the larva. In 

 the larval stage this Crabro is subject to the attacks of the larva of 

 a small hymenopteron, Pteromalus apum, shown magnified (Fig. 9, 

 PI. II.). It is parasitic on many bees and wasps, and is a member 

 of the large family ChalcididcE, of which over one thousand British 

 species have been recorded. Each larva of Crabro leticostotmis 

 attacked by this little fly is destined to support several specimens 



