210 



MR. A. M. ALTSON ON THE LIFE-HISTORY AND 



that tlie seDse-organs in the antenna? and the palps of the 

 ovipositor had suddenly received the odour of the carrion aud 

 stimulated the insect to oviposit. The males are also attracted 

 hy carrion — apparently a sexual tropism to enable them to locate 

 the females. Marshall (3) observes :— " They " (both sexes) " scent 

 the aroma of carrion at a surprising distance, as I once had 

 occasion to observe in watching the remains of a dead rook, upon 

 which they descended in constant succession, apparently from the 

 sky, like vultures. The males generally alighted on blades of 

 grass close to the attractive object, as if to wait for their 

 partners, without interi'upting tliem in their unsavoury occu- 

 pation." 



As soon as the females have alighted, they begin theii- search 

 for the larvae, and if the initial efibrt to insert the ovipositor is 

 successful, they remain depositing eggs until they die, either from 

 exhaustion or because their task is completed. A few have been 

 observed to leave the larva? and go in search of food and not 

 return the same day. 



Only one egg is deposited in each larva by an individual 

 female, at least, under conditions wliich are approximately 

 natural— e., where the larva has means of escape by disappearing 

 into the meat or earth. 



The ovipositor is inserted diagonally under the integument of 

 the larva when the attack takes place in the thoracic or 

 abdominal regions. The larva makes every effort to escape, 

 wriggling and squirming, and frequently damaging the female. 

 These frantic efforts to escape are put an end to by the effect of a 

 poison injected with the insertion of the ovipositor. The 

 immediate effect of the insertion of tlie ovipositor is to cause the 

 larva to vomit and void. The poison produces a paralyzing 

 effect, and causes the larva to conti-act and then lie motionless 

 whilst the egg is deposited. This operation varies in time, and 

 may take 30 seconds to 5 minutes* — the more exhausted the 

 female is, the longer it takes. 



The "temporary paralysis" of the larva lasts from one to two 

 minutes, so that when an exhausted femaJe delays the with- 

 drawal of the ovipositor the larva endeavours to release itself ; 

 normally though, when the ovipositor is withdravvU, it is still 

 motionless, and remains so for some seconds. The female then 

 Rioves off in search of another victim. The first movements of 

 a larva recovering from the " temporary paralysis" are to extend 

 itself to its full length, and then, still slightly under the influence 

 of the poison and the unpleasant ovipositor, it goes through a 

 series of extraordinary convulsive and constrictive movements, 

 which ripple the integument either from the cephalic to the 

 anal end or vice versa, as though it was endowed with intelligence 



* One female, which had -.lOt oviposited in more than a dozen larvge, was ol)served 

 to retain the ovipositor within a larva for 21 minutes, and as the initial dose of 

 poison did not suffice to keep it motionless, further doses were apparently 

 administered each time it moved. Needless to say, this larva died. 



