To Charles D. Wise, Esq., Estate Office, Toddington, Winchcombe, Gloucestershire.
Torrington House, St. Albans,
April 16, 1896.
Dear Mr. Wise,—If it would not give you too much trouble I should be very glad of some information about the case of Caddis worms attacking water-cresses. You will know these grubs quite well as the creatures that go about in shallow ponds or ditches with a case formed round them. Sometimes this is of very little shells, but at home the commonest kind was made of little morsels of rush or stick, with little leaves webbed up with it.
There is a very large trade in water-cresses from the little river here, but there are such quantities of trout in it, that probably these keep the Caddis worms in moderate limits, and I only now and then see their flies, the so-called “Water moths” in the summer. Mr. Richard Coe, Weston Farm, Guildford, has kindly sent me some excellent specimens of Caddis worms and cases, which I am very glad to have. The chief natural helpers against over-presence of Caddis worms appear to be fish of various kinds, but the increase of birds which naturally feed on fish—herons, &c.,—destroys the balance of nature, and Caddis worms increase.
[Miss Ormerod, quoting Mr. Coe in her Report for 1896, says (p. [156]):—
“Whenever we find a bed of cresses attacked, we clear away all the plants, drain off the water, and leave the bed perfectly dry for two or three weeks in the autumn, previous to the winter planting. If afterwards we find traces of the worm, we wait until the plants are well established, then we increase the volume of water and swim the bed, and pass the backs of wooden rakes over the tops of the plants very thoroughly. This process brings the bulk of the worms to the surface, and they are let off down-stream with the surplus water.”
Water moth, magnified, and lines showing natural size (after Westwood); Caddis worm “cases” of Limnephilus flavicornis, magnified.
FIG. 33.—CADDIS WORMS, LARVÆ OF CADDIS FLY OR WATER MOTH, MORMONIA NIGROMACULATA.
To Dr. Fletcher she also wrote as follows:—