IV INTRODUCTION. By L. B. Prout. 



a few naturalists there. From Peru and other parts of tropical South America very extensive collections have 

 of recent years been received in Europe, provided with accurate data as to the season of capture, and yet they 

 reveal scarcely a trace of seasonal variation. In Europe, seasonal dimorphism is well known in the genera 

 Cosymhia, Lythria, Eilicrinia and Selenia ; but even in this region it cannot be regarded as a very general occurrence. 



The habits of the Geometridae are about as varied as would be expected amongst so large a family. In- 

 formation is, however, regrettably deficient as regards the habits of most of the exotic "species. Some points 

 have been discussed above, in connection with protective resemblance. As there indicated, the usual time 

 of flight is in the evening or later at night, although during the day they can, for the most part, be rather easily 

 disturbed from their resting-places in the trees, bushes or herbage. In Britain, of which I can speak from per- 

 sonal experience, the favourite time of flight is about sunset or in the early dusk, although a few species {Abraxas 

 grossulariata, CromMis elinguaria, Cidaria pyraliata, etc.) do not usually become active until towards midnight. 

 The flight is usually rather gentle and not extremely long-sustained; but Ourapteryx and a few others dash about 

 more wildly and irregularly. The great majority are provided with tongues and feed more or less at various 

 flowers, flowering rushes or other natural sweets, but are on the whole much less greedy feeders than the Noc- 

 tuidae, and although a long list might be made of the species which have occasionally been attracted by ,, su- 

 gar", yet they visit it only in quite small numbers, and on many nights do not seem to be attracted to it 

 at all. On the other hand most, if not indeed all, of the species may be attracted by light, and they are usually 

 easily captured in this way. Eupithecia and many others do not, as a rule, continue to flutter round long when 

 under the influence of this attraction, but settle down quietly with the wings pressed flat against the glass, or 

 sometimes on some object near by — especially if there be a white wall or ceiling within the radius of the light. 



The localities most favoured are the edges of woods or bushy places, or rough broken ground with a 

 wealth of vegetation. Open grass-land is apparently much less productive. A fair number of species, 

 however, reach high altitudes in the mountains and high latitudes in the Arctic Region. Generally speaking, 

 the species which reach the extreme limits seem able — perhaps on account of the comparative absence of com- 

 petition — to propagate themselves in great abundance, and there are several records of the appearance of a 

 particular species in Arctic Norway or Iceland m prodigious numbers, the air being sometimes filled with them 

 as though there were a snow-storm. The subfamily which thrives best under rigorous climatic conditions is the 

 Larentiinae, and it is probable that a previous (even where there is not a present) circumpolar distribution ac- 

 counts for the fact that the great majority of the species common to the Palearctic and Nearctic Regions belong 

 to this subfamily. It is interesting that a good proportion of the Geometrid fauna of the inhospitable Magellan 

 and Tierra del Fuego district and almost all the Geometridae we have yet seen from the Falkland Islands belong 

 also to the Larentiinae. The Hemitheinae and Acidaliinae, by contrast, are very poorly, when at all, represented 

 in the extremes of northern and southern latitude. 



On account of their comparatively weak flight, there are very few migrants among the Geometridae. 

 Orthonama ohstipata and Rhodometra sacraria are the chief examples, and little, if anything, is known as to the 

 means of their dispersal. Occasionally, however, and apparently under the same meteorological influences which 

 prompt the migratory birds, certain common sedentary species migrate in enormous swarms. Thus on 

 Heligoland, in three or four different years, such companies of Erannis defoliaria, and aurantiaria have been 

 observed, always travelling westward; and on at least one occasion thousands of Ennomos quercinaria. 



The Geometridae are of no ascertained value to economic entomology. On the other hand one species in 

 particular, and several others to a lesser degree have to be reckoned among the prominently injurious insects. 

 The outstanding example is Operophtera hrumata, Avhose ravages among fruit-trees, and the best means for its 

 destruction, have been discussed in every European work on economic entomology since the Swedish Academy 

 invited essays on the subject in the days of Linnaeus. Fortunately as its $ is apterous, the warfare against this 

 pest is waged under somewhat more advantageous conditions than would otherwise be the case, it being possible 

 to destroy immense numbers on the tree-trunks before they reach the branches. Incredible as it may appear, 

 it is now, however, definitely stated by several independent and trustworthy witnesses, that the ^ is sometimes 

 capable of carrying the $ in copula, although one may still venture to doubt whether this is more than a flutter 

 which could scarcely lift her in an u^Dward direction. The larvae of some other species multiply in certain sea- 

 sons so as to be scarcely less destructive, either to orchards or to forest trees, as the case may be, but it is not 

 necessary to particularize these in this place. 



The Geometridae are small or moderate-sized (rarely large) moths, usually of slender build. Palpus 

 rarely very strong, third joint scarcely ever with remarkable modifications of shape or scaling. Antenna very 

 variable in form. Thorax rarely strongly crested. Abdomen with basal cavity beneath the pleura of the (much 

 swollen) second segment. Legs seldom very hairy, but ^J hindtibia often furnished with strong hair-pencil. Fore- 

 wing usually with four or five subcostal veins, the fourth and fifth (and nearly always the third) stalked to- 

 gether; various forms of anastomosis frequent. Second radial from centre of discocellulars, or above, scarcely 

 ever connate with third radial. First submedian wanting. Hindwing with costal vein making a bend into humeral 

 angle, never connected or anastomosing with subcostal beyond end of cell, second radial never connate with 

 third, often absent, first submedian wanting. Egg flat. Larva a looper, usually with only two pairs of claspers. 



