76 ENTOMOLOGICAL NEV/s. [March, '03 



introduced. It was while attempting to procure such succu- 

 lent morsels that I happened to make the observation I am 

 about to record. I had removed a one chambered mud-nest 

 of Pelopaeus [the nest probably belonged to the blue mud- 

 dauber (/*. caeruleus Lin.) which was the most common form in 

 the neighborhood, though P. cevietitaritim Drury was sometimes 

 met with] from a protected portion of the north wall of a 

 stone house, and on opening the sealed receptacle I did not 

 find, as I had expected, a larva surrounded by its paralyzed 

 prey nor a pupa beginning to show the definite shape of the 

 parent form, but instead a densely woven grey cocoon which 

 fitted snugly against the concave wall. When with difficulty 

 I tore open the tough cocoon in order to see its contents, there 

 fell from it a full grown female Mutilla vesta. It was evident 

 that the ^'g^ of the Mutilla had been placed by some unknown 

 means in the mud-dauber's nest and had there hatched out. 

 The larva having consumed the stored up spiders and the larva 

 of Pelopaeus, had completed its growth and spun its cocoon 

 in the mud-cell of its host, and was aw^aiting the time when it 

 should emerge as a perfect Mutilla. 



Mutillidae in Texas are always found running on the sur- 

 face of the ground or rarely climbing the stems of low plants. 

 In the case above considered, the mother Mutillid, in order to 

 place her eggs in the Pelopaeus nest, was forced to leave the 

 ground and creep up a rough stone w^all for a vertical distance 

 of about ten feet where the nest was situated. If Pelopaeus 

 is the normal host of M. vesta, the latter undoubtedly has 

 more difficulties to surmount than does her European sister, 

 M. europoea, which is said to live in the nest oi Bom bus agro?^m 

 and to deposit her egg in the growing Bombus larva by means 

 of her ovipositor which she thrusts through the aperture made 

 in the wall of the cell by the worker Bombus for the purpose 

 of passing in food. It does not seem possible that the female 

 Mutilla vesta, in the act of ovipositing could have perforated the 

 hard mud wall of the cell in order to place her egg in the con- 

 tained larva ; but it seems probable that the egg was deposited 

 by her among the earliest spiders stored and before the Pelo- 

 paeus had laid her own egg and sealed the chamber. Further 



