42 Mr. F. Smith's Observations on the Economy of 



cessfuUy confutes the theory of St. Fargeau, who observing that, 

 amongst this tribe, many species were destitute of cilia on their an- 

 terior tibiae, and also of spines externally down the posterior pair, 

 suggested the probability of such species being parasitic; the P. 

 j)unctum is one of the species tlius circumstanced, and here we have 

 a clue to the complete explanation of the apparent anomaly — an 

 insect which constructs mud cells has no need of the cilia or 

 'spines, so useful to an insect which forms its burrows in sand ; the 

 cilia on the anterior tibiae forming as it were a brush, with which 

 to sweep out the particles of sand, from time to time, in forming its 

 burrow, and the spines, placed exteriorly on the posterior tibise, 

 which in burrowing are placed against the sides of the tunnel, 

 which gives the creature a purchase whilst scratching, or disen- 

 gaging the sand with its mandibles. 



The structure of the Pompilus in question naturally calls to the 

 mind of an Hymenopterist another insect, which long suffered 

 under the imputation of being a parasite — I allude to Pelopceus. 

 My friend, the late Edward Doubleday, had, it is true, ever since 

 his return from America, asserted the contrary, but it remained 

 for Mr. Gosse, in the second volume of the "Zoologist," to pub- 

 lish one of the most amusing and graphic sketches of insect archi- 

 tecture which I ever had the good fortune to fall in with ; this 

 set the matter, as regards the Pelopccl, at rest ; and if any be 

 wanting, I thing the discovery of the P. punctum being a con- 

 structor of mud cells, similar to those of Pelopceus, furnishes de- 

 cisive testimony against the theory of St. Fargeau, 



My own experience does not furnish a single instance of para- 

 sitism in the whole tribe of fossorial Hijmenoptera ;* and, if I am 

 not trying your patience too far, I will take this opportunity of 

 adding the results of my own observations in further elucidation 

 of this interesting subject. I will, in the first instance, make a few 

 observations upon the various insects mentioned in Mr. Shuckard's 

 paper above alluded to. 



The first insect I would observe upon is the Sapyga quadrigut- 

 tata, which I have captured conveying its prey, a small Lepidop- 

 terous larva, and have also found its cells, formed in a sand-bank, 

 filled with similar larvae ; when the larva of Sapyga is full fed, it 

 spins a tough brown cocoon, very similar to that of an Osmia. 

 The genus Trypoxybn, were St. Fargeau's theory correct, would 

 be parasitic, but I have repeatedly observed the different species 

 conveying their prey, and have also repeatedly bred the insects. 



* I here speak of British insects; the Scoliadce are known to be parasitic — and 

 I suspect that Tiphia is the parasite of Aphudius. The Mutilluicc are also said to 

 be paiasitic. 



