16 WHEELER— THE PARASITIC ACULEATA. 



Pompilus rufipes (now called Psammo chares) have acquired the 

 habit of robbing other individuals of their prey which they then 

 bury and furnish with an egg. They even wage fierce battles for 

 one another's spiders. These observations acquire added interest 

 in connection with another very closely related species, P. pectinipcs, 

 which, according to Ferton (1901, 1902, 1905), enters the sealed 

 nests of P. rufipes, eats its tgg and deposits its own on the spider. 

 Ferton was thus led to advance the opinion that we hav2 in pecti- 

 nipes a parasite that has just become detached phylogenetically from 

 its host species. 



" The parasitic habit," he says, " would therefore appear to have been 

 built up in the following manner : P. rufipes, living in colonies, has acquired 

 the habit of stealing the prey of its neighbor and even of fighting for the 

 possession of prey not its own. Some individuals finally learned to steal the 

 spiders that had been buried, either by driving away the rightful owner while 

 she was sealing her burrow, or by ferreting through the soil occupied by the 

 colony in search of sealed burrows. Their descendants, inheriting this habit, 

 gave up constructing a nest and transporting the stolen prey to it and left it 

 in the cell where it was discovered, simply substituting their egg for the one 

 it bore. Thus P. pcctinipes was evolved, scarcely distinct from the maternal 

 stock in many of its anatomical characters but become a parasite on the spe- 

 cies from which it arose." 



In Sweden Adlerz (1910, 1912) found that P. campestris ex- 

 hibits a similar parasitism on P. unguicularis and P. acitleatits on 

 P. rufipes and funiipennis, and Ferton (1891) has shown that P. 

 viaticus and pulcher resemble rufipes in their habit of appropriating 

 the prey of other individuals of their own species. 



Finally we have among the Psammocharids a distinct and pecu- 

 liar genus, Ceropalcs, all the species of which are parasites on other 

 genera of the family. Lepeletier (1827) was the first to regard 

 Ceropales as a parasite, but Walsh was the first to breed it from 

 the nest of another Psammocharid. Riley and Walsh (1869), in 

 their paper on wasps and their habits, state that a male Ceropales, 

 which they described under the name C. rufiventris, but which is 

 now known as C. robinsoni Cresson, emerged from a mud cell that 

 had been constructed and provisioned by Agenia homhycina. That 

 they were fully aware of the importance of this observation is clear 

 from the following remark: 



