252 



KNOWLEDGE 



[November 1, 1890. 



functions. The insect is said to require in all about eleven 

 weeks to reach maturity, but the exact duration of its 

 metamorphoses is no doubt greatly dependent upon the 

 regularity and amount of the supply of food. In the 

 adult condition it can certainly endure long fasts with im- 

 punity ; De Geer kept several in a sealed bottle for more 

 than a year without food. It is also a well-kno-n-n fact 

 that bugs sometimes absolutely swarm in houses that have 

 for a long time been uninhabited. In such cases it is 

 ob\ious that they have managed to exist without access to 

 human blood ; still it does not necessarily follow that they 

 have been entirely without food of any kind, and when we 

 remember that their human parasitism is probably an 

 acquired habit, their appearance under such conditions 

 will be less difficult to understand. 



It has been supposed that they are able to abstract 

 juices sufficient to support life from the wood- work of 

 buildings, and if we take mto consideration the absorptive 

 properties of unpainted soft woods, such as deal, it seems 

 far from incredible that such may be the case. That an 

 insect which has been accustomed during the greater part 

 of its individual life to subsist upon animal matter should 

 suddenly change its diet and feed upon vegetable sub- 

 stances, or upon mere inorganic moisture, and the slight 

 amount of organic matter that may contain in solution, 

 would in most cases be an unprecedented proceeding, and 

 there are hosts of insects which would rather starve than 

 do it. But it is not at all an imusiial circumstance in the 

 order Hemiptera, and several of the wild bugs seem to be 

 quite indifferent as to whether they are supplied with an 

 animal or a vegetable diet. Another suggestion by which 

 it has been proposed to account for their presence in \m- 

 inhabited houses is that the colony having been estab- 

 lished during the human occupation, they have, since the 

 desertion of the premises by their hosts, preyed upon one 

 another, and so sustained life. But an obvious objection 

 to the theory is that by such a course their numbers would 

 be speedily thinned, and the colony would probably soon 

 become extinct, a resvJt which by no means talMes with 

 experience. If in such cases the bugs really found any 

 difficulty as to the commissariat, of course migration 

 would be open to them, and it is difficult to believe that, 

 enterprising as they are, they would not avail themselves 

 of such an expedient, if reallv hard pressed by famine. 



While it may be admitted that the hard-skinned, un- 

 growing adidts can subsist for long periods without food, 

 it is probable that the younger and softer skinned forms, 

 in whose bodies the vital processes are more rapid, require 

 more frequent supplies. Such, at any rate, is the expe- 

 rience of those who have attempted to rear any of the 

 wild species of Hemiptera with which our woods, fields, 

 and hedges swarm. As the surest and safest way of 

 avoiding bugs in the house is the cultivation of scrupidous 

 cleanliness, it would seem probable that the miscellaneous 

 material included under the name " dirt," which is, much 

 of it, of organic origin, may contribute in some way to 

 their support ; but still it must be borne in mind that, 

 owing to the peculiar structure of their mouth organs, 

 whatever be the nature of the material ft-om which they 

 derive their food, only its liquid portions can be partaken 

 of. Anyhow, there seems little doubt that human blood 

 is not an absolute necessary of life to this disgusting para- 

 site, and perhaps may be more correctly regarded as a 

 luxury ; and it is quite possible that before its association 

 with mankind, Acanthin lectvtaria may have been a 

 purely vegetable feeder, subsistmg on the sap of trees. 

 Southall declares that he fed the numerous families he 

 kept on such food as this, using chiefly deal for the pur- 

 pose. Hard woods, such as oak, walnut, and mahogany. 



or scented woods such as cedar, they failed to extract any 

 nutriment from, and died if confined with these alone. 



In our last paper a passing reference was made to the 

 ( '(iri.ni', as exliibiting some of the most beautiful develop- 

 ments of hind-wings' to be met with in the whole order 

 Hemiptera. The photographs accompanying the present 

 article give the opportunity of contrasting the fore-wing 

 of one of these insects with the rudimentary scale-like 

 elytron of the bed-bug, as well as of comparing it with that 

 of the field-bug figured last month. It will be observed 

 that there is a similar composite structure of the wing — 

 corium, clavus, and membrane being present, though no 

 part of the first-mentioned is divided off from the main 

 body to form a cuneus. It is perhaps difficult to realise at 

 first sight that insects so widely different in appearance 

 and habitat as the ' 'orira and the Bed-bug, nevertheless 

 belong to the same order. Though so utterly dissimilar 

 in shape, however, the two insects are constructed on 

 what is essentially the same type or plan, their mouth 

 organs being almost identical in form and arrangement, 

 and the method of their growth and development, and the 

 cycle of changes they pass through, entirely similar. 

 Hence we see tiiat an msect's systematic position is to be 

 determined, not by its habits or method of life, nor by 

 the actual form even of its body or of many of its organs, 

 since similarities in these respects often co-exist with 

 profound differences in other and more important parti- 

 culars ; and, on the other hand, the greatest divergence in 

 habits, form of body, and nature of limbs and antennae, 

 may be observed in insects that are in other and more 

 essential respects closely alike. Attention should there- 

 fore be paid specially to three points in determining the 

 systematic position of any insect, \'iz. the nature of its 

 mouth organs, the structure of its wings, and the kind of 

 metamorphoses it passes through ; insects which are 

 alike in these respects may be regarded as intimately 

 related to one another, and as referable to the same 

 order, however they may differ in other ways. 



Like all other insects, bugs, of course, breathe by in- 

 haling air, not at the mouth, but at certain openings in 

 other parts of the body, whence it is passed along delicate 

 tubes {tnicln'ie) to all parts of the system. The stigmata, 

 or openings to the trache*, are in the present instance 

 extremely small, and therefore not easy to trace. They 

 are situated on the under surface of the abdomen, not far 

 from the edge of the body. Perhaps the best way to see 

 them is to remove the ohitinous band which forms the 

 boundary of any of the central abdominal segments on 

 the under side, and, after relieving it of any adhering 

 viscera, to examine it with the compound microscope. A 

 low power will be sufficient to show the stigmata, one on 

 each side, as minute roundish openings surroimded by a 

 rim-like lip. From these pass the main tracheal trunks, 

 the branches of which, like tiny threads of silver, run 

 hither and thither over the body. Their silvery appear- 

 ance is due to the air they contain. The body of the 

 living or fresUy-killed bug is usually sufficiently trans- 

 parent for some of the chief branches to be traced from 

 the outside. 



The accompanying photographs show the corresponding 

 organs of a water-beetle and a silkworm, and will serve 

 to indicate, more clearly than any verbal description can 

 do, the sort of thing that is to be looked for in a dissec- 

 tion. The structural details cannot be properly made out 

 till the tubes are removed from the surrounding organs 

 and freed from the air they contain. The fine thread 

 which projects round their inner walls prevents coUapse ; 

 and so well does it perform its function that even in the 

 dead and th-ied bodies of bugs, however ancient, such as 



