THE AMERICAN ENTOMOLOGIST. 



133 



more than any other group of insects. From .a 

 lot of the kind of mud-cells sketched in Figure 

 K Jo, c, we long ago bred great numbers of a mi- 

 nute Chalcis&Y (Fteromalus) only oue-twcntieth 

 of an inch long; and from a lot of those shown 

 in Figure 10.5, ri, about a dozen specimens of a 

 beautiful undescribcd Ichneumon-fly, about one- 

 third of an inch long, banded with black and 

 white, and with a white horse-shoe ou the hind 

 part of its thorax, to which we liave given the 

 manuscript name of the Horse-shoe Ichneumou- 

 fly (Mesostenusfemtm-equinum) . 



It is well known to entomologists that among 

 the solitary Bees — whose habit it is to provision 

 tlieir nests with pollen, and not, after the fashion 

 of the Digger Wasps and solitary True "Wasps, 

 with living insects — there arc many genera, 

 physically incapacitated from collecting pollen, 

 which lay their eggs surreptitiously in the nests 

 of the true pollen-collecting Bees, and thus ap- 

 propriate for their own offspring the rich stores 

 laid up for anotiier's. Not only in the case of 

 the group of Spider Wasps just now referred to 

 (Ayenia), but in that of several other genera of 

 Digger Wasps {Trypoxi/lon, Pe/op(eus and 

 Sapyya), has a similar habit been inferred by 

 several authors to prevail. We suspect that, in 

 these particular cases, erroneous inferences have 

 been drawn from seeing the supposed Guest 

 Wasps entering old l.ist year's nests made by 

 true Digger W.asps, or by Bees, which nests 

 they afterwards appropriate for their own use, 

 haviug tirst in many instances repaired and re- 

 modeled them. As regards the tirst of the tliree 

 genera enumerated above {Trypoxylon). West- 

 wood has shown this to be so ;* and, at the risk 

 of being tedious, we will give some additional 

 proofs of this and certain other analogous facts, 

 which have been observed by ourselves for a 

 long series of years. 



Almost every American knows the so-called 

 '• mud-dabs," constructed by the common Mud- 

 dauber (Fig. 101), to be composed ofoneormoi'e 

 layers or tiers of clay tubes, arranged side by 

 side like a set of " Pan's pipes," and cemented 

 on to some surface pretty well protected from 

 the weather. In a i)articLilar locality — the rocky 

 cliff's near Black Hawk's Watch-tower, in Rock 

 Island county. Ills. — we have always, for many 

 years back, found these " mud-dabs " to contain 

 in the winter months the cocoons of the wasp that 

 makes them, and those of another Digger AVasp 

 of a uniform black color, and belonging to a very 

 distinct family {Trypoxylon albitarse, Fiihr). 

 Figure 107, promiscuously intermixed in .ibout 

 equal proportions. There can bo no mistake 



• Introduclion, Ac, If., p, 104. 



[Fig. 107.] 



CoUirs— I'olisln.-a black, with (lie- liiml paw.'^ whitish. 



here, because the cocoon of the former, after 

 stripping off" the thin semi-opaque flossy outer 

 membrane, characteristic of all those made by 

 Digger-wasps, is about eight-tenths of an inch 

 long, elongate oval, Ave times as long as wide, 

 of a shining transparent tawny color, as thin 

 almost as gold-beater's skin, and with the tail 

 end docked, thickened and blackened; while 

 the cocoon of the latter has a mere vestige of 

 outer membrane, and is only about half an 

 inch long, only thrice as long as wide, cylindri- 

 cal but often with the head end expanding, like 

 a cooper's rivet, into a more or less wide flange, 

 of a dull opaque black color except the head 

 end, which is ash gray, with the tail end docked 

 but not otherwise dift'ering from the rest of the 

 cocoon, and the whole of a pretty firm and solid 

 consistence. In most cases the elongate mud- 

 cell of the Mud-dauber, when it has been ten- 

 anted by the Black AV'asp spoken of above, is 

 partitioned off' by a clay diaphragm in the mid- 

 dle into two cells, each of which contains a dis- 

 tinct cocoon : but occasionally such a cell con- 

 tains but a single cocoon, especially when the 

 cell is rather shorter than usual. It is well 

 known that the Mud-dauber provisions its nest 

 M'ith spiders, and fragments more or less com- 

 plete of spiders may often be found in the cells 

 occupied by its cocoons. Precisely the same 

 thing occurs in the cells tenanted by the cocoons 

 of the Black Wasp, showing that its larva must 

 h.'ive fed upon spiders just as does that of the 

 Mud-dauber. Lastly, from the cocoons shaped 

 like a cooper's rivet, isolated in a separate ves- 

 sel, we have repeatedly bred, not the Mud- 

 dauber (Fig. 104), butthe Black Wasp (Fig. 107). 

 Now, here is a mass of evidence amounting 

 to what lawyers would call prima f<trie proof, 

 that this Black Wasp is really a Guest-wasp, 

 not building .and provisioning any nest for itself, 

 but laying its eggs in the nest built and provis- 

 ioned by the Mud-dauber, and thus fraudidently 

 appropriating for its own future progeny, the 

 provision of spiders, laid up for the progeny of 

 the Mud-dauber, by that poor hard-working in- 

 <lnstrious insect. Otherwise, whv should the 



