April 1, 1893.] 



KNOWLEDGE. 



61 



^^ AN ILLUSTRATED ^K< 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: APRIL 1, 1893. 



CONTENTS. 



Caterpillars' Dwellings — I. By E. A. Btjtlee 



Woodpeckers. I'.y IIaket F. AViTHEnBT 



Deep Sea Deposits. — Second Paj^er. By the Rev. H. N. 



Hutchinson, B.A., F.G.S 



The Distribution of tlie Stars. By Miss A. M. Cleeke ... 



Thie 1) Argus Nebula. By A. C. Eanyard 



Science Notes 



Letters: — E. Ltdekker; Chaeles Xielsen; B. J. Hopkins; 



W. H. S. MONCK ; Gr. E. MiTTON ; EdWTN AnTHONT ; 



W. Stanifoeth 



Tine Constitution of Gases. By J. J. Stewart 



The Face of the Sl<y for April. By Herbert Sadler, 



F.R.A.S 



Chess Column. By C. D. Locock, B.A.Oxon. 



PAGE 



61 

 (U 



65 

 6fi 

 6!) 

 70 



73 

 75 



78 

 79 



CATERPILLARS' DWELLINGS.-I. 



By E. A. BuTLEK. 



AMONGST the caterpillars of butterflies and moths, 

 the architectural instinct is developed chiefly in 

 two directions. Some live in communities and 

 construct a common dwelliog-place ; others, which 

 are solitary in habits, either rear amongst the 

 foliage of their food-plant some sort of tent or covering to 

 serve as a snug and safe place of retreat and shelter, or 

 else construct a portable receptacle into which the greater 

 part of the defenceless body is thrust while the insect 

 travels in search of food. In the formation of a common 

 dwelling-place, no such wonderful ingenuity is displayed as 

 characterizes the workmanship of bees, ants, or wasps, and 

 for this several reasons may be assigned. In the first 

 place, the architects are not perfect insects, but only 

 immature creatures which live a very vegetative sort of life. 

 Their communities, again, do not reach that high degree 

 of organization which is implied in the term " social " ; 

 they form what were called by Kirby and Spence " im- 

 perfect societies," i.e., the individuals of the tribe, though 

 sharing in the construction of the abode which serves as a 

 common means of defence, do not contribute to the common 

 support, nor supply one another's needs in the way of food, 

 but each looks after its own interests, and recks not what 

 may befall the rest. And again, though they are larval 

 forms, each is able to provide for itself from the moment 

 of hatching ; thus there are no helpless young to be tended, 

 and this at one stroke removes the necessity for the multi- 



farious duties that occupy so much of the time of truly 

 social insects, and at the same time renders any elaborate 

 structure unnecessary. Lideed, there is little more than 

 their common descent from one batch of eggs, and the 

 presence of the common food in their vicinity, to induce 

 them to form any bond of association at all. Hence they 

 are more appropriately styled gregarious than social. The 

 common domicile, moreover, is not made by the heaping 

 up of particles of foreign matter, nor by the excavation of 

 galleries in earth or wood, so that no toilsome journeys in 

 search of buUding materials, nor hard labour in the exca- 

 vation of tenacious matter are requisite. The caterpillars' 

 lives are much too fully occupied with eating to leave time 

 or energy for such undertakings. The material made use 

 of is simply silk spun from their own bodies, and the 

 supply keeps pace with the increasing necessities of the 

 case, till at last an extensive web is formed, whose dimen- 

 sions are such that it lodges the whole community and 

 still leaves plenty of room to spare. 



There are not many British species that adopt this 

 practice ; those that do fall chiefly into three groups. One 

 of these occurs amongst that interesting division, the rather 

 large-sized and heavy-bodied moths called Bombyces, 

 some of the densely hairy larvse of which we have already 

 discussed ; the second, amongst a set of small moths called 

 " knot-horns " ; and the third is a genus called Hypo- 

 nomeuta, which belongs to the division containing the 

 smallest Lepidoptera in the world, and known as the 

 Tinese. To take these latter first. Most owners of gardens 

 sooner or later come into collision with representatives of 

 the genus Hi/ponowi'uta. They are called " small ermine 

 moths" (Fig. 1), and the different species are all very similar, 

 having narrow, whitish or slate- 

 coloured fore-wings with rows of black 

 dots, and lead-coloured hind-wings 

 with long fringes, and a clear trans- 

 parent space at the base of the wing. 

 The expanse of wings is generally 

 under three-quarters of an inch ; but 

 when the moth is at rest, with its 

 wings closed, it becomes a narrow 

 cylindrical object, showing nothing more than the spotted, 

 ermine-like fore-wiugs. 



Hedges of hawthorn, apple trees, and euonymus shrubs 

 are the particular kinds of vegetation most attacked by 

 these elegant but destructive little pests. The young, fresh 

 shoots of the shrubs are found spun together in early 

 summer by a quantity of silken threads like a cobweb, and 

 in the midst of the mass are to be seen a number of small 

 black-spotted caterpillars, which are of a smoky or yellowish 

 colour, according to the species. On being disturbed they 

 WTiggle violently, and either crowd together side by side in 

 the centre of the web, or drop out of it, descending to the 

 ground at the end of an improvised thread. Under the 

 shelter of the web, they devour the surface of the foliage 

 of the shrubs, thereby causing the remainder of the leaves 

 to wither and shrivel up and turn brown. Apparently the 

 caterpillars do not suffer fi-om the assaults of birds, for the 

 sticky and clinging threads would greatly incommode and 

 annoy any bird that ventured to tamper with them ; and 

 as pretty good proof that they are amongst Nature's 

 favourites may be cited their extreme abundance, which 

 is often far greater on the Continent than even in this 

 country, so that their ravages become sometimes a source 

 of serious loss to the agriculturist. It is thus clear that 

 they have found web-making an exceedingly paying 

 transaction. 



The early history of these little creatures is rather peculiar. 

 The eggs are laid on the stems of the food-plant at the end 



Fro. 1.— Small Ei-- 

 iiiine Moth (Si/pono- 

 mcida padflla). 



