LARViE OP DEILEPHILA EUPHORBI^E. 321 



which is best adapted for conspicuousness in any usual position. The 

 larvae so invite attention as to suggest inedibility, and an experiment I 

 tried confirms the suggestion. The very obliging landlord of the 

 Thermes Hotel readily agreed to shut up for a few hours eight or ten 

 chickens that he had, varying in size from three parts to full growth, 

 so as to make them a little hungry, and I threw among them sixteen 

 larvas, mostly full grown or nearly so. The fowls, which were in a 

 confined space about eight feet by four, on bare ground, in general took 

 no notice of them, though the caterpillars made themselves very 

 conspicuous by crawling as well as by their colours, even when the 

 birds trod on them as they often did. One of the fowls, however, 

 attacked a large larva, giving it five or six pecks, but then desisted. I 

 am almost sure it was this fowl — certainly it was one of the only two 

 brown ones — that almost immediately afterwards visited the water- 

 trough in which it dipped its beak many times, a thing I did not see 

 done by any of the others. Another fowl pecked once or twice at a 

 larva, but did not return to the charge. I tried the fowls again later, 

 with similar general results. I may mention that I had collected 

 many of the larvae in the hotel grounds over which the fowls often 

 wandered, so that the larvte could scarcely have been unknown to them. 

 I could not try the experiment with lizards, as these were exceedingly 

 scarce at Vals-Platz, and I did not see more than three in all my walks 

 there. The larv* were in thousands, distributed over the hillside from 

 4000 to 5500 feet above the sea, perhaps higher. Possibly the scarcity 

 of lizards in this valley, which is a cool and humid one, having a general 

 inclination towards the north, may make it a successful breeding-ground 

 for the insect. I had written thus far, when I referred to Weismann's 

 Studies in the Theory of Descent, and found there that though a lizard 

 would not eat the somewhat similar larva of D. galii (a species found 

 by me in this valley in small numbers) it at once attacked and 

 swallowed a large larva of D. euphorbiae ; and it seems possible that 

 the scarcity of lizards and the distastefulness of these larvae to birds — 

 at all events to some birds — may have a connexion with their abundance 

 in this locality. Of wild birds there was the scarcity usually observable 

 in Switzerland. I saw none but redbilled choughs in large numbers, 

 but not seen by me lower than about 6000 feet, and a few other crows 

 and hawks including one or two kestrels. One would like to know what 

 it is that prevents D. euphorbiae from increasing to an overwhelming 

 degree. Suppose a pair produces not less than 150 eggs, it must happen 

 that, taking one year with another, 148 die before becoming parents. 

 The larvte seem hardy and are easily reared. I have not found them 

 attacked by insect parasites nor by disease, nor have I heard that they 

 are so. The perfect insect is known to fly far, and doubtless large 

 numbers take flight into the neighbouring regions where lizards 

 abound ; possibly this may be one of the means by which their numbers 

 are kept down. May I venture to suggest that books which aim at 

 giving a complete description of insects, by describing their lives and 

 habits as well as their structure, should, at least in dealing with the 

 dominating types, endeavour to give not merely what they feed on, but 

 what feeds on them and to what extent — their effective enemies, as well 

 as their commissariat — facts of cardinal importance in judging of the 

 causes which lead to their prevalence or to their disappearance ? Without 

 full information as to the destructive as well as the productive forces, 



