THE AMERICAN ENTOMOLOGIST. 



131 



gradually become shorter weaker and less num- 

 erous. Another school of pliilosophers will 

 maintain, that its legs are bristly, in order to 

 complete the Plan of the Creation, and carry 

 out the System of Nature, and g;ive full and free 

 expression to the Thoughts of the Creator. 

 Which explanation be the more rational and in- 

 telligible, the reader must judge for himself. 



Two other such cases, which may be explained 

 upon similar principles, have been briefly re- 

 ferred to by Dr. Packard in his (luide to the 

 Study of Insects (pp. 165 and 169). In these 

 cases two species, belonging respectively to two 

 genera of Digger "Wasps (Larrada and Sphex) , 

 all the other known species of which burrow in 

 the ground to form their nests and have legs 

 covered with thorns and bristles, have been as- 

 certained to make their nests above ground in 

 the fold of a leaf. AVe might consequently ex- 

 pect them both, if they were both primordially 

 created with such abnormal instincts, to have 

 perfectly smooth legs like the True Wasp 

 (.EM»?ene«)figured below (Fig. 110, «),whicii gen- 

 erally attaches its nest to the stem of some weed 

 or to a leaf in the open air. It is pretty nearly 

 but not exactly so; for it is recorded that one of 

 these insects has its front legs perfectly smooth, 

 and that the other one (the Sphcx) has its front 

 legs almost but not quite destitute of spines and 

 bristles. We liavc but to refer to the sketch 

 of a dilTercnt species of this latter genus (Sphe.v) 

 given above in Figure 99, the Ichneumon-like 

 Digger Wasp, which species is known to be a 

 burro wer in the ground, to see how very dif- 

 ferently its front legs are armed. The difference 

 can be explained in the mode that best suits 

 the reader. 



But, from discoveries of our own, we are 

 enabled to point out still another link in the 

 chain which connects the Digger Wasps with 

 the True Wasps, and still another thread in the 

 complicated web which binds together all 

 living organisms, wlietiier animal or vegetable. 

 There is a genus, or, as Mr. Cresson considers 

 it, a sub-genus {Ayenki) of the Spider Wasps 

 (Pompilus sub-family) — a very extensive gronj) 

 of tlie Digger Wasps, all the other genera of 

 which, with a single exception, to be hereafter 

 noticed, burrow in the ground to form their 

 nests, and have thorny and bristly legs. Tliis 

 genus (Agenia), however, has perfectly smooth 

 legs, with the exception of a very few species, 

 which have the merest rudiments of bristles or 

 thorns, on their thighs or shanks. Singular to 

 relate, although the French entomologist, St. 

 Fargeau, has described thirty-five species of 

 these smooth-legged Spider Wasps, found in 



various parts of the world, and although our 

 countryman, Cresson, has described as many as 

 twenty-eight species, found in Xorth America, 

 yet, up to this day, nobody can tell for certain 

 what are the general habits of the genus, from 

 anything that has as yet been published. 

 Shuckard, judging from .the structure of its 

 legs, guesses that it must bore into wood to 

 make its nest.* St. Fargeau, for the same 

 reason, guesses that these smooth-legged Spider 

 Wasps must be what may be called " Guest 

 Wasps," building no nests of their own, but 

 depositingtheir eggs, like the European Cuckoo 

 and our American Cow-bird, in the well-pro- 

 visioned nests of allied nest-building species. f 

 The real truth of the matter is, that they are nei- 

 ther Wood-borers nor "Guest Wasps ;" but make 

 little " mud-dabs " of their own, usually under 

 the bark of standing trees, or under prostrate 

 logs, in which, precisely as does the well- 

 known Mud-dauber, figured above (Fig. lOi), 

 they rear their y-oung. Hence, we see at once 

 why, like this last-named wiisp, they have 

 smooth, ' or very nearly smooth, legs. The 

 reason is simple. Thorns and bristles on their 

 legs, though of great service for digging nests 

 in the ground, or in decayed wood, v^ould be 

 of no manner of use to them in building nests 

 with mud ; and therefore, they either have 

 none at all, or mere rudimental ones. 



Why certain species have rudimental thorns 

 on their legs, may be explained in either of the 

 two modes referred to above. Why, on the 

 other hand, certain other species have perfectly 

 smooth legs, we can readily understand if we 

 adopt the former of these two hypotheses ; but, 

 if we adopt the latter hypothesis, this fact be- 

 comes an insoluble and nnintelligible enigma. 



AVe present herewith sketches drawn from 

 nature, of the " mud-cells " made by four dis- 

 tinct species of this very remarkable genus, 

 which, hitherto, has been such a puzzle to the 

 entomological student. All four kinds of cells 

 are occasionally connected logetlier, end to end, 

 like a string 

 of beads, as 

 i) shown in the 

 figures of three 

 of them. These 

 three, a, b, and 

 c, are given in 

 c..ir,i-riax-Tcii..«. Figure 10J,and 



the fourth in Figure 106, a, all of them of ' 

 the natural size; and along with the fourth 

 mud-cell, we give an enlarged drawing of 



•Quoted by Westnood, Introduction, II, p 20S. 

 tSt. Fargeau, Hi/menopleres, HI, p. 441. 



