AucxDST 1, 1892.] 



KNOWLEDGE 



145 



■nhich, oil the contrai-y, calmly acquiesce in the appropria- 

 tion which renders much of their labour abortive ; hence 

 the parasites fly freely about amongst them, and pass in 

 and out of the burrows without opposition. An interesting 

 observation of Mr. F. Smith may be quoted in point. The 

 host in this case was a brownish stout-bodied bee, the 

 female of which (Fig. 3, a) is a good deal like an Anthaphoni 



A B 



Fig. S. — A. Solitary bee {Eiicera loiigicornis, female). B. Its 

 parasite (Xomada sexf-asciala), slightly magnified. 



in shape, while the male may be easily distinguished from 

 all other British bees by its enormously long antennsp, 

 which are nearly as long as the body, whence its name 

 F.wcni loni/iconiis, both parts of which refer to this feature ; 

 when freshly out it is a handsome insect with rich brown 

 hairs on its thorax, but it soon fades on exposure to 

 the sun and becomes weatherworn, old specimens 

 appearing with dirty grey thorax and ragged wing-edges. 

 The Xomailn parasitic upon this is one of the largest and 

 finest of the genus ; it is called A', .s/wfuscintti (Fig. 3, b), 

 in reference to the six yellow adornments of its abdomen, 

 ■which consist of three bands and three pairs of spots. Mr. 

 F. Smith says that, whilst watching a colony of Km-era, 

 the males of which were sportively flying round in circles, 

 while the females were intent upon their maternal duties, 

 returning every now and then heavily laden from their 

 expeditious, he saw the piarasites sometimes enter the 

 burrows. Sometimes a laden female would return to its 

 burrow just after a Xamadn had entered it. On discovering 

 the presence of the intruder she did not give battle, though 

 much the stouter and heavier insect, but would simply 

 retreat, fly off to a little distance, and wait patiently till 

 the parasite issued from the burrow, when she would 

 return to deposit her load. At a later season he unearthed 

 some of the cells, and found the young parasites in them, 

 two in each cell. The bees of this genus, Xomoda, have 

 not got their parasitism so definitely settled as those of 

 the former genus Mehctn ; some of them are attached to a 

 single species of industrious bee, but others are less 

 particular, and depend upon a variety of hosts. Moreover, 

 they do not, as a genus, confine themselves to a single 

 genus of hosts, but divide their attentions amongst several 

 that are of similar habits. 



In the leaf-cutter bees we have a very peculiar and 

 distinct set of insects, and, as might be expected, then- 

 parasites are equally distinct. The hosts line the cells 

 they construct for their yoimg with fragments of the leaves 

 of shrubs, and everyone has probably noticed the ap- 

 pearance the leaves of rose-bushes present in gardens when 

 they have been mutilated by these insects for this purpose. 

 Semi-circular pieces are seen to have been cleanly cut out 

 from the sides of the leaf; several such cuttings being 

 often made from the same leaf when it is large enough. 

 The bees themselves are not so often noticed ; they belong 

 to the genns Mniiichlle, and are remarkable, not only for 

 the leaf-cutting habit, but also because they have the 

 whole of the under surface of the abdomen densely covered 

 with hairs, which they use as their pollen-collecting 

 apparatus. After visits to flowers, this part of the body 



Fio. 4.— Section of 

 cell of leaf-cutter bee 

 (^eg a chile), with 

 cocoon. Magnified 



2 diameters. 



may be seen to be heavily laden with the precious grains. 

 The construction and furnishing of the cells is quite a 

 work of art. A tunnel is first excavated to a length 

 sufficient to accommodate perhaps half a dozen or more 

 cells; the cells themselves (Fig. 4), which are composed 

 entirely of leaves, are fitted into this, 

 and placed one after the other along 

 its length. An oval leaf fragment 

 being placed so as to cover the end 

 and a little of the sides of this tunnel, 

 a number of semi-oircular, neatly cut 

 fragments are next placed round the 

 sides in regular order and laid close, 

 one upon another, each partially over- 

 lapping its neighbour, thus making a 

 lining to the tunnel of several layers 

 thick ; the number of layers appears 

 to depend upon the nature of the 

 material in which the tunnel is ex- 

 cavated, and its condition as regards 

 moisture, kc. : a specimen now before 

 me has four such layers. A mass 

 of mixed honey and pollen is now introduced, an egg is 

 laid, and then some rin-iilnr pieces of leaves brought to 

 cover up the opening, just in the same way as the house- 

 wife puts a layer of paper over the jam in the recently 

 filled jar ; the specimen above mentioned has also four of 

 these. A second cell is then built up in a similar way at 

 the end of this, and so on till the whole set is complete : 

 the whole tunnel is thus lined with leaves, and there are 

 at regular intervals cross partitions, which are the tops 

 and bottoms of the cells, and the leaves serve to protect the 

 food from contamination by the walls of the tunnel, as 

 well as to prevent loss of its more liquid component by 

 soakage. When the larva has devoured the food, it is full 

 grown ; it then forms an oval lining of silk in the cylindrical 

 cell, taking care to shut in the excrement which has 

 accumulated during its larval life, between the walls of 

 this silken lining and the outer leafy hangings of the cell. 

 Within this cocoon it becomes a pupa. 



These leaf-cutters are subject to the parasitism of a 

 genus of cuckoo-bees called CnUoxi/s, which are black, 

 almost hairless, cruel-looking insects, with pointed abdomen. 

 They present a great contrast to our last illustrations, the 

 Xoiini(hr, for instead of the gay colours, graceful proportions, 

 and fragrance which distinguish that genus, they exhibit 

 a sombre and funereal appearance and a less elegant form, 

 and give out a disagreeable odour, which, no doubt, helps 

 to secure them from attack. It is evident that they must 

 keep a constant watch on the doings of their hosts, in 

 order that they may introduce the egg just in the nick of 

 time, after the cell has been sufficiently provisioned, and 

 before the first layer of its many-plated lid has been put 

 on, and hence they are usuaUy to be found in the 

 neighbourhood of the burrows of the leaf-cutters. 

 (To be continued.) 



ON THE CAUSE OF EARTHQUAKES. 



By the Eev. H. N. Hutchinson, B.A., F.G.S. 



RECENT investigations have shown that terni lirmn 

 is a phrase indicating a condition of things which, 

 scientifically, has no existence. The crust of the 

 earth is in a state of constant movement. Geo- 

 logists have begun to study systematically the 

 phenomena of earth-movements of all kinds, and some of 

 the results are such as cannot fail to interest even the 

 general reader. We aU have a stake in the condition of our 



