1966] 
Cooper — Eumenine Wasps 
245 
the egg, and the duration of instar- 1 entered in the table includes 
the time (about 45 minutes) involved in hatching. The average 
duration of instar- 1 after rupture of the chorion is 16 hours. 
4. Exit from the nest 
All who have reared large numbers of mason wasps in the labora- 
tory from intact nests are familiar with the sharp, rasping scratches 
which foretell emergence of the imagos, as well as with the dessicated, 
powdery debris of the cut walls and terminal plug that remains long 
after the wasps have cleared the nest. But all are equally familiar 
with nests from which few or no wasps finally emerge, despite earlier, 
prolonged audible indications that emergence had been attempted. 
When such nests constructed in burrows are cut open, dead wasps 
may be found jammed in single file at the terminal plug, with the 
remains of dismembered and chewed sibs pushed to the rear. I sus- 
pect that such observations have led to the quite general belief that 
mason wasps simply cut their way out with their mandibles, as well 
3S to the general wonder that they can do so from nests so hard, 
cement-like and thick as those, say, of masarid wasps (e.g., see David- 
son 1913, Ferton 1921, Hicks 1927, 1929). That they sometimes 
fail to do so seems to be taken as only natural. 
It is true that the eumenid and masarid wasps (at least Psendo- 
masaris vespoides [Cress.] ) do cut their way out with their mandi- 
bles, but the task is lightened in at least two ways. For one, it is 
easier to pass through a plug or wall from the inside than from the 
outside. This is because the inner faces of plugs and crosswalls are 
necessarily irregular and less compact in texture, as well as somewhat 
convex, for the masoning wasp is unable to control the irregularities 
and to press them down tightly with her head. For this reason por- 
tions of the inner faces of walls and plugs more readily break off 
when pried or rasped. For another, these wasps treat refractory 
regions just as their mothers did when first compounding the mortar; 
the eclosing adults soften the walls by moistening them to mud, as 
Nielsen (1932) first discovered in the case of emerging Symmorphus 
smuatus (Fab.). Reg'ons of walls softened in this way may then 
be cut with ease. 
This certainly is the case for emerging Ancistrocerus antilope 
(Panz.), A. cats kill (Sauss. ), A. tigris (Sauss.), Symmorphus crista- 
tus (Sauss.), Par ancistrocerus fulvipes (Sauss.), Monobia quadridens 
(Linn.), Rygchium foraminatum (Sauss.), and R. megaera (Lepel.) 
among the eumenines, as well as for Pseudomasaris vespoides 
(Cress.), all of which I have studied. When wasps fail to cut their 
way out of a nest, it is often the case that one or more plugs are so 
thick and unworkable (a terminal plug may be as much as 20 mm 
