THE AMERICAN ENTOMOLOGIST. 



131 



gradually become shorter weaker and less inun- 

 eroii.s. Another school of philosophers will 

 maintain, that its legs are bristly, in older to 

 complete the Plan of the Creation, and carry 

 out the System of Nature,' and give full and free 

 expression to the Thoughts of the Creator. 

 AVhich explanation be the more rational and in- 

 telligible, the reader must judge for himself. 



Two other such cases, which may be explained 

 upon similar jjrinciples, have been brietly re- 

 ferred to by Dr. Packard in his Guide to the 

 Study of Insects {^^. 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. "We might consequently ex- 

 pect them both, if they were both primordially 

 created with such abnormal instincts, to have 

 perfectly smooth legs like the True AVasp 

 (iJ?<jHe?ies)flgured below (Fig. 1 10, ly), which 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 Sphex) has its front 

 legs almost but not quite destitute of spines and 

 bristles. AVc have but to refer to the sketch 

 of a difl'erent species of this latter genus {Sphex) 

 given above in Figure 09, the Ichneumon-like 

 Digger AVasp, which species is known to be a 

 burrower 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 "VVasps with 

 the True Wasjis, and still another thread in the 

 complicated web which binds together all 

 living organisms, whether animal or vegetable. 

 There is a genus, or, as !Mr. C'resson considers 

 it, a sub-genus (v((/c»u'«) of the Spider Wasps 

 {Pompihis sub-family) — a very extensive group 

 of the 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. This 

 genus (Ar/enia), 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 AVasps, 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 tills 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 uests 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, ill which, precisely as does the well- 

 known Mud-dauber, figured above (Fig. 104), 

 they rear their young. Hence, we see at once 

 why, like this last-named wasp, 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, would 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 ruiliinental 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 nnintelligiblfe 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 together, end to end, 

 [KiK in.-) 1 like a string 



of beads, as 

 shown in the 

 figures of three 

 of them. These 

 three, «, 6, and 

 c, are given in 

 coior-ciaj -yciinw. Figure 105,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 Westwood, Introduction, 

 tSt. Fargeau, Hijmenopleres , III. p + 



p 20S. 



