256 Transactions. — Zoology. 



Art. XXIII. — A Fly and a Spider (Pompilidae, Salius mo- 

 nachus, Srn. ; and Porrhothele antipodiana). 



By Ambrose Quail, F.E.S. 



[Read before the Wellington Philosophical Society, 18th March, 1903.] 



Plate XXIX. 

 It is proverbial that spiders are cunning and ferocious, and it 

 is popularly supposed that their physical strength surpasses 

 the strength of flies, yet just as tiies are helpless under a 

 spider's bondage, so, literally speaking, in the hands of some 

 flies are spiders helpless. 



To begin with, a class of flies having four wings, a sting, 

 and which construct a nest wherein they deposit eggs and 

 their young afterwards mature, are known to naturalists as 

 Hymenoptera Aculeata. Examples of this class are the bees 

 and wasps. In my young days I derived amusement from 

 the antipathy that spiders have for flies of this class. A strong 

 cunning spider will lie low and concealed when some one or 

 other of these four-winged flies happens to be in its vicinity. 

 Put a wasp in the web of a spider — one of the Epeira_ group — 

 and watch results. (The species on which I used to experi- 

 ment was E. diadema.) The spider almost invariably would 

 be most anxious to be relieved of her visitor, to effect which 

 she will frequently sacrifice part, often a large part, of her 

 laboriously constructed web. In feverish haste, keeping all 

 the time well out of reach, the spider severs the strands above 

 its captive, the weight of the insect breaking away the lower 

 strands. 



I question much whether E. diadema gained knowledge of 

 the formidable character of its captive from actual individual 

 experience ; certainly they fear the consequences of coming to 

 close quarters. Is the antipathy instinctive ? Can it be that 

 generations of spiders have witnessed the hapless fate of their 

 neighbours when some four-winged Hymenopteron, descending 

 from above, like an eagle upon a lamb, has carried away a 

 spider captive, to incarcerate her in a cell or mud-hole, para- 

 lysed and helpless, doomed to form the fresh meat on which 

 the young of its captor will feed and mature? 



The advantage possessed by the fly is in the powerfully 

 poisonous secretion which it injects by means of its sting into 

 some portion of its victim's anatomy, with instantaneous 

 paralysing effect. Peckham,* having broken off the leg of a 

 small crayfish, induced a wasp to sting it at the exposed part 



* " Instincts and Habits of the Solitary Wasps." 



