LARVA OF DEILEPHILA EUPHORBIZ. 321 
which is best adapted for conspicuousness in any usual position. The 
larvee 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 
larvee, 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 m 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 larve in the hotel grounds over which the fowls often 
wandered, so that the larvee 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 larve 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 larvee to birds— 
at all events to some birds—may have a connexion with their abundance 
in this locality. Of wild birdsthere 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. ewyhorbiae 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 larvee 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, 
