464 



NA TURE 



[Oct. 8, 1874 



the first brood of larv.ie found during the early part of May, the 

 second toward the end of June, and disappearing with the dying 

 of tlie leaves, tlie latter part of July. 



The second species is a still more invariable living accompani- 

 ment of both kinds of Sanacenia mentioned. By the time the 

 wliitish efflorescence shows around the mouth of the pitcher, the 

 moist and macerated insect-remains at the bottom will be found 

 to almost invariably contain a single whitish, legless, grub or 

 "gentile," about as large round as a goose-quill, tapering to the 

 retractile head, wliich is furnished with two curved, black, 

 sharp hooks, truncated and concave at the posterior end of the 

 body. 



This worm riots in the putrid insect remains, and when fed 

 upon them to repletion bores through the leaf just above the 



Fig. 1. — Xiinthopiera Scmicrocea. rt, egg, enlarged, the natural size indi- 

 cated at side : 1^, r, larva, back and side views : ti, chrysalis ; e, moth, 

 normal form, with wings expanded ;/, pale variety with wings closed. 



petiole and burrows into the ground. Here it contracts to the 

 pupa state, and in a few days issues as a large two-winged fly, 

 which I have described in the Transactions of the St. Louis 

 Academy of Science as Sarcophaga sarracenin — the Sarracenia 

 Flesh-fly. 



The imnsense prolificacy of the Flesh-flies, and the fact that the 

 young are hatched in the ovaries of tlie parent before they are 

 deposited by her on tainted meat and other decomposing or 

 strong-smelling substances, have long been known to entomolo- 

 gists, as has also the rapid development of the species. The 

 viviparous habit among the Muscid;c is far more common than 

 is generally supposed, and I have even known it to occur witli 

 the common housc-flv, which normally lays eggs. It is also 

 possessed by some Qistridre, as, I have shown in treating of 

 CEstnis oc'is, the Sheep Bot-fly. 



But the propensity of the larvce for killing one another and 

 their ability to adapt themselves to different conditions of food 

 supply are not sufficiently appreciated. I have long since known, 

 from extensive rearing of parasitic Tachinidx-, that when, as is 

 often the case, a half-dozen or more eggs are fastened to some 



dS / 



/r 



Fig. i.Sarcophaga Samuenia. a, larva ; i. pupa ; c, fly, the hair lines 

 showing average natural lengths ; d, enlarged head and first joint of 

 larva, showing curved hooks, lower lip (f-), and prothoracic spiracle ; 

 e, end of body of same, showing stigmata (/) and prolegs and vent ; 

 /(, tarsal claws of (ly with protecting pads ; i, antenna of same. All 

 enlarged. 



caterpillar victim only large enough to nourish one to maturity, 

 they all hatch and commence upon their common prey, but 

 that the weaker eventually succumb to the strongest and oldest 

 one, which finds the juices of his less fortunate brethren as much 

 to his taste as those of the victimised caterpillar. Or, again, 

 that where the food-supply is limited in quantity, as it often is 

 and must be with insects whose larva; are parasitic or sarcopha- 

 gous, such larvx have a far greater power of adapting themselves 

 t o the conditions in which they find themselves placed, tlian have 

 herfjivorous species under like circumstances. 



Both these characteristics are strongly illustrated in Sarcophaga 

 sarracciiuT. Several larva;, and often upwards of a dozen, are 

 generally dropped by the parent fly within the pitcher ; yet a 

 fratricidal warfare is waged until usually but one matures, even 

 where there appears macerated food enough for several. And if 

 the Xanthoptera larva closes up the mouth of the pitcher ere a 

 sufficient supply of insects have been captured to properly 

 nourish it, this Sarcophaga larva will nevertheiess undergo its 

 transformations, though it sometimes has not strength enough to 

 bore its way out, and the diminutive fly escipes from the 

 puparium, only to fiud itself a prisoner unless deliverance comes 

 in the rapture or perforation of the pitcher by the moth larva or 

 by other means. This rupturing of the pitcher does not unfre- 

 quently take place, for Dr. Mellichamp writes under date of June 

 27 as follows: — "Most old leaves now examined— I might 

 almost say all — instead of being bored, seem ripped or torn, as 

 if by violence, apparently from without. Vou see occasionally 

 slireds of the leaves hanging. Surely the legless arva of Sar- 

 cophaga cannot do this 1 What then— loads, or frogs, or craw- 

 fish abounding i.i these moist, pine lands? or rather is not the 

 fat maggot the oco ision of the visits of the quail which lately I 

 have observed here ? " 



[Here follow some technical facts and descriptions of interest 

 only to specialists.] 



These two insects are the only species of any size that can in- 

 vade the death-dealing trap with impunity wliile the leaf is in 

 full vigour, and the only other species which seem at home in 

 the leaf are a minute pale mite belonging apparently to Nolo- 

 thynii, in the GamasidK, and which may tjuite commonly be 

 found crawling within the pitcher ; and a small Lepidopterous 

 leaf-miner, which I have not succeeded in rearing. There must, 

 however, be a fifth species, which effectually braves the dangers 

 of the bottom of the pit, for tlie pupa of Sarcophaga is some- 

 times crowded with a little chalcid parasite, tlie parent of which 

 must have sought her victim while it was rioting there, as larva. 



But all other insects, so far as we know, tumble into the tubn 

 and there meet their death. The moth is doubtless assisted in 

 wallcing within the tube by the spurs on the legs which it, iy 

 common wilh niojt other moths, possesses; while the Flesh-fle 

 manages to hold its own by its widely extended legs and stout 

 bristles. Dr. Mellichamp says that when disturbed it buzzes 

 violently about, just as if an animated sheep bur had fallen into 

 the tube — not apt to go down, because it will hitch and stick, 

 and finally, by main force, it generally emerges, but once in a 

 while also succumbs. 



Two questions very naturally present themselves here: — (i) 

 Wliat gives the Flesli-fly more secure foothold on the slippery 

 pubescence than the common house-fly exhibits ? (2) \Vhat 

 en.ibles the larva of the Flesh-fly to withstand the solvent 

 property of the fluid which destroys so many other insects? I 

 can only offer, in answer, the following sugg stions : the last 

 joint of the tarsus of the common hoasc-fly has two movable, 

 sharp-pointed claws and a pair of pads or " pulvilli," These 

 pads were formerly supposed to operate as suckers, and all 

 sorts of sensational accounts of this wonderful sucker have been 

 given by popular writers, who forgot that there are any number 

 of minute insects having no such tarsal apparatus, which are 

 equally indifferent to the laws of gravitation so far as walking on 

 smooth, upright surfaces, or on llie ceiling, is concerned. In 

 reality, these pads are thickly beset on the lower surface with 

 short hairs, most of which terminate in a minute expansion kept 

 continually moist by an exuding fluid — a sort of perspiration. 

 Take the human hand, moistened by perspiration or other 

 means, and draw it, with slight pressure, first over a piece 

 of glass or other highly polished surface, and then over some- 

 thing that has a rougher surface, such as a planed board, a 

 papered wall, or a velvety fabric, and you will experience much 

 greater adhesion to the smoother objects, and may understand 

 the important part which these moist pads play in the locomo- 

 tion of the fly ; they also act, in part, like tlie cushions of a cat's 

 paw in protecting and preventing abrasion of the claws, which 

 are very useful on the rougher surfaces, where the pads are less 

 serviceable. 



Now, compared vi\i\\ Miisca jL'iiwsliiii, the claws of A/rcc/Z/rt^v; 

 sarracotiiC are much the longest and strongest, and the pads 

 much the largest, presenting three or four times the surface. 

 These differences are, 1 think, sufficient to explain the f;rct tlut 

 wliile the common fly walks with slippery and unsteady gait on 

 the smooth pubescence (the retrorse nature of this pubescence 

 sufliciently explaining the downward tendency of the movements), 

 its sarcophagus congener manages to get a more secure fooling ; 



