LICHENS AS FOOD 397 



are, however, not equally palatable. Bitter' observed that the insect Psocus 

 {Orthoptera) had a distinct preference for certain species, and restricted its 

 attention to them probably because of their chemical constitution. He noted 

 that in a large spreading thallus of Graphis elegans on holly, irregular bare 

 spots appeared, due to the ravages of insects — probably Psocus. In other 

 places, the thallus alone had been consumed, leaving the rather hard black 

 fruits (lirellae) untouched. In time the thallus of Thelotrema lepadinuni, 

 also a crustaceous lichen, invaded the naked areas, and surrounded the 

 Graphis lirellae. The new comer was not to the taste of the insects and was 

 left untouched. 



Petch^ says that lichens form the staple food of Termes monoceros, the 

 black termite of Ceylon. These ants really prefer algae, but as the supply 

 is limited they fall back on lichens, though they only consume those of 

 a particular type, or at a particular stage of development. Those with 

 a tough smooth cortex are avoided, preference being given to thalli with a 

 loose powdery surface. At the feeding ground the ants congregate on the 

 suitable lichens. With their mandibles they scrape off small fragments of 

 the thallus which they form into balls, varying in size from r5 mm. to 2'5 mm. 

 in diameter. The workers then convey these to the nests in their mandibles. 

 It would seem that they carry about these balls of food, and allow the ants 

 busy in the nest to nibble off portions. Lichen balls are not used by termites 

 as fungi are, for "gardens." 



Other observations have been made by Paulson and Thompson' in their 

 study of Epping Forest lichens: "Mites of the family Oribatidae must be 

 reckoned among the chief foes of these plants upon which they feed, seeming 

 to have a special predilection for the ripe fruits. We have had excellent 

 specimens oi Physcia parietina spoiled by hidden mites of this family, which 

 have eaten out the contents of the mature apothecia after the lichens have 

 been gathered. One can sometimes see small flocks of the mites browsing 

 upon the thallus of tree-dwelling lichens, like cattle in a meadow." The 

 Oribatidae, sometimes called beetle-mites, a fam.ily of Acarinae, are minute 

 creatures familiar to microscopists. They live chiefly on or about mosses, 

 but Michael^ is of opinion that a large number frequent these plants for the 

 fungi and lichens which grow in and about the mosses. In Michael's 

 Monograph of British Oribatidae, four species are mentioned as true lichen- 

 lovers, Leiosoma palmicinctiiin found on Peltigera canina and allied species ; 

 Cepteus ocellatus and Oribata parmeliae which live on Physciae, the lajtter 

 exclusively on Physcia {Xanthoria) parietina; and Scutovertes maadatus 

 which confines itself to lichens by the sea-shore. Another species, Notaspis 

 lucorum, frequents maritime lichens, but it is also found on other substrata; 



' Bitter 1899. ^ Fetch 1913. ' Paulson and Thompson 1913. 



* Michael 1884. 



