Wild Birds and Distasteful Insect Larvæ

Abstract

DR. W. E. COLLINGE gives in NATURE of July 24 some most interesting details about the distastefulness of insects to birds. He observes that both the larva and imago of Abraxas grossulariata are eaten by various species. I would like to add the following observaitions:—During the last few years I have bred several I thousand larvæ, including those of A. grossulariata, in order to study their genetics. Owing to the impossibility of setting all the imagines, a certain number were set free as soon as recorded. In this way I have thrown out of my window imagines of the following species:—A. grossulariata, Spilosoma mendica (larvæ and imagines), and both type and melanic forms of Tephrosia consonaria, Boarmia consortaria, and B. abietaria. I have noticed the following points:—(1) The birds round the house, chiefly sparrows, would eat the imagines of all five species, but A. grossulariata the least readily, tearing off the wings and devouring the body on the spot (it was too late in the year for them to be feeding young). (2) My larvæ of S. mendica were suffering from a disease (a filter-passer, I believe, for smears revealed no micro-organisms), and when an entire brood was past hope I used to throw them into the garden. Some were dead and many dying, but they were cleared away in a few minutes, in spite of their evil smell. (3) The imagines of B. consortaria and B. abieiaria were eaten with the utmost avidity. No sooner had one or two insects been thrown out than a number of birds, would crowd round waiting for the next, and if this were hidden in the ivy round the house they would hunt for it until it was found. On one occasion some insects were hidden in a flower-pot on the window-sill, but the birds soon found them, and would afterwards return to the edge of the pot, as if waiting for more. These birds would even carry off dry pinned insects, possibly for their nests. The fact that birds will not eat A. grossulariata readily, but will eat the diseased larvæ of S. mendica, seems to support Mr. Speyer's view, especially since the parasites mentioned do not live in the alimentary tract. For this reason they contain no proteolytic enzymes, and can therefore be of no conceivable harm to young birds.