INDIEECT BENEriTS DERIVED FROM INSECTS. 247 



their food from the insect tribes : even in winter the pupae of 

 Lepidoptera, as Mr. White tells us, are the grand support of 

 those that have a soft bill.^ 



I shall close my list of the indirect benefits derived from 

 insects, by adverting to the very singular apparent subserviency 

 of some of them to the functions of certain vegetables. 



You well know that some plants are gifted with the faculty 

 of catching Jlies. These vegetable Muscicapce, which have 

 been enumerated by Dr. Barton of Philadelphia, who has 

 published an ingenious paper on the subject^, may be divided 

 into three classes : — First, those that entrap insects by the 

 irritability of their stamina, which close upon them when 

 touched. Under this head come Apocynum androscBmi- 

 folium, Asclepias syriaca and curassavica, Nerium oleander, 

 and a grass described by Michaux under the name of Leersia 

 lenticularis. The second class includes those which entrap 

 them by some viscosity of the plant, as many species of 

 Rhododendron, Kalmia, Robinia, Silene, Lythriim, Populus 

 halsamifera, &c.'^ And under the third class will arrange 

 those which ensnare by their leaves, whether from some irri- 

 tability in them, as in Dioncea, Drosera, &c., or merely from 

 their forming hollow vessels containing water into which the 

 flies are enticed either by their carrion-like odour, or the 

 sweet fluid which many of them secrete near the faux ; as in 

 Sarracenia, Nepenthes, Aquarium, Cephalotus, &c., the tubular 

 leaves of which are usually found stored with putrefying in- 

 sects. In this last class may be placed the common Dipsacus 

 of this country, the connate leaves of which form a kind of 

 basin round the stem that retains rain-water, in which many 

 insects are drowned. To these a fourth class might be added, 

 consisting of those plants whose flowers smelling like carrion 

 (^Stapelia hirsuta, &c.) entice flies to lay their eggs upon them, 

 which thus perish. 



I White's Selborne, i, 181. 2 philos. Mag. xxxix. 107. 



3 Small flies are sometimes found sticking to the glutinous stigma of some of 

 the Orchideae like birds on a limed twig (Sprengel, Entdecktes Geheimniss, 21.) ; 

 and ants are not unfrequently detained in the milky juice which the touch of even 

 their light feet causes to exude from the calyxes of the common garden lettuce. — 

 Ann. of Bot. ii. 590. 



R 4 



