LICHENS AS FOOD 399 



A minute organism, Hymenobolina parasitica 1 , first described by Zukal 

 and doubtfully grouped among the mycetozoa, feeds, in the plasmodium 

 stage, on living lichens. The parasitic habit is unlike that of true mycetozoa. 

 It has recently been recorded from Aberdeenshire. 



b. INSECT MIMICRY OF LICHENS. Paulson and Thompson 2 give instances 

 of moth caterpillars, which not only feed on lichens, but which take on the 

 coloration of the lichens they affect, either in the larval or in the perfect 

 moth stage. "One of the most remarkable examples of this protective 

 resemblance to lichens is that of the larva of the geometrid moth, Cleora 

 liclienaria, which feeds upon foliose lichens growing upon tree-trunks and 

 palings, and being of a green-grey hue, and possessed of two little humps 

 on many of their body-segments, they so exactly resemble the lichens in 

 colour and appearance as to be extremely difficult of detection." Several 

 instances are recorded of moths that resemble the lichens on which they 

 settle : perfect examples of such similarity are exhibited at the Natural 

 History Museum, South Kensington, where Teras literana, Moma orion, and 

 other moths are shown at rest on lichen-covered bark from which they can 

 hardly foe distinguished. 



Another curious instance of suggested mimicry is recorded by G.E. Stone 3 . 

 He spotted a number of bodies on the bark of some sickly elms in Massa- 

 chusetts. They were about ^ of an inch in diameter " with a dark centre 

 and a drab foliaceous margin." They were principally lodged in the crevices 

 of the bark and Stone collected them under the impression that they were 

 the apothecia of a lichen most nearly resembling those of Physcia hypoleuca. 

 Some of the bodies were even attached to the thallus of a species of Physcia; 

 others were on the naked bark and had every appearance of lichen fruits. 

 Only closer examination proved their insect nature, and they were identified 

 as belonging to a species Gossypina Ulmi, an elm-leaf beetle common in 

 Europe where it causes a disease of the tree. It had been imported into 

 the United States and had attacked American elms. 



It is stated by Tutt 4 that the larvae of many of the Psychides (Lepi- 

 dopterd) live on the lichens of trees and walls, such as Candelaria concolor, 

 Xanthoria parietina, Physcia pulverulenta and Buellia canescens, and that 

 their larvae pupate on their feeding grounds. Each species makes a "case" 

 peculiar to itself, but those of the lower families are usually covered exter- 

 nally with grains of sand, scraps of lichens, etc. The " case " of Narcyria 

 nwnilifera, for instance, is somewhat raised on a flat base and is obscured 

 with particles of sand and yellow lichen, giving the whole a yellow appearance. 

 That of Luffia lapidella is roughly conical and is held up at an angle of 30 

 to 45 when the larva moves. The " cases " of Bacotia sepium are always 

 upright; they measure about 5*5 mm. in height and 275 mm. in width and 

 1 See also p. 267. 2 Paulson and Thompson 1913. 3 Stone 1896. 4 Tutt 1900, p. 107. 



