RELATIONS OF ANTS TO OTHER INSECTS. 347 



way the Russian author interprets also the waxy secretion which may fall 

 on and pollute the limpid drops of excrement, but this is certainly not 

 true of all wax secreting aphids. The common alder blight (Pem- 

 fihiyns tcsscllatiis) secretes wax in abundance, but is, nevertheless, 

 eagerly attended by several species of ants. It is difficult to understand 

 why some aphids should repel the advances of the ants when other 

 species apparently derive so much advantage from their companionship, 

 for, although no complete list has as yet been published of the species 

 of aphids and the ants with which they are always or only temporarily 

 associated, we know, nevertheless, that a few species of the former 

 are definitely symbiotic with ants, and that there are others with more 

 or less pronounced proclivities of the same kind. Wasmann (1804) 

 cites Forda fonnicaria as regularly myrmecophilous and Shouteden 

 ( 1902 ) mentions Paraclctns ciinicifonnis as living only in the nests of 

 ants. Both of these species are radicicolous, that is, they occur on the 

 roots and not on the aerial portions of the plants. But there is also, 

 at least in North America and Europe, a long series of radicicolous 

 aphids that occur with more or less frequency in ant nests. Shouteden 

 records no less than seventeen species, representing nine genera (Gcoica, 

 Forda, Tetrancitra, Schizpneura, Pcuiphiyiis, Trania, Chaitophorus, 

 J [>Jtis and Microsiphum ) as occurring in the nests of Lasius nigcr 

 alone. In North America varieties of this ant, and especially L. ncarc- 

 ticiis, brci'icornis and the various members of the subgenus Acantho- 

 myops, harbor in their subterranean galleries a great many aphids. 

 Mrs. W. P. Cockerell (1903) has shown that these include species of 

 Tychca and Forda (F. kingi, inter jecti, lasii and pallid ula}. Mord- 

 wilko cites Lasius brnnucns as living exclusively at the expense of 

 species of Stoinacliis, which are found on the stems and leaves of 

 plants. Further studies of ants and aphids by investigators familiar 

 with the species of both of these groups will unquestionably bring to 

 light many additional instances of such intimate symbiosis. 



Much of what lias above been said of the aphids will apply also to 

 the scale-insects and mealy-bugs (Coccida? ). These are even more sed- 

 entary than the aphids, and may also occur on both the roots and aerial 

 surfaces of the plants. They are, however, more largely confined to 

 warm countries, whereas aphids are more abundant in temperate 

 regions. Abdominal tubules are absent in coccids, but they protect their 

 bodies by secreting a covering of powdery white wax or a hard or 

 tough scale. Like the aphids, they excrete honey-dew, often in con- 

 siderable quantities, from the anal orifice. The manna of Biblical 

 tradition is now known to be the honey-dew of one of these insects 

 ( Gossyparia mannifera ) which lives on the tamarisk. This excretion 



