REVISION MALACOSOMA HUBNER IN NORTH AMERICA 21 



The spumaline serves several functions. It is an adhesive which holds 

 the eggs in place. It is not w^aterpi-oof as has been erroneously supposed 

 in the past, but is definitely hygroscopic (Hodson and Weinman, 1945), 

 absorbing moisture from the air which helps to prevent the eggs from 

 drying out. It also protects the eggs from parasites, which are successful 

 only in attacking eggs exposed at the edges of the egg mass. It is worth 

 noting that the eggs of M. tigris are not covered by spumaline, yet 

 they do not dry out and parasitism was very low in those collected 

 during this study. The lack of spumaline in this species, however, possi- 

 bly is compensated for by the eggshell being somewhat thicker than that 

 of those species which cover the eggs with spumaline. It is also interest- 

 ing to note that the reservoirs of the accessory glands of female tigris 

 contain as much spumaline as those of any other species, yet only 

 enough spumaline is used to hold the eggs in place. 



The spumaline of all species except M. calif ornicum is homogeneous. 

 In some, but not all, populations of californicum, the spumaline contains 

 numerous minute, dark objects which appear to be scattered through- 

 out, more or less at random; these are termed "specks" (fig. 118). They 

 should not be confused with particles of dirt which collect on the outer- 

 most bubbles of spumaline and inside broken bubbles, but which are 

 not present on the inner unbroken layers of bubbles. These specks are 

 discussed in some detail since they are useful in separating certain 

 populations of Af. californicum from other populations oi calif ornicum, and 

 from M. incur vum. 



It is not difficult to observe the specks on fresh egg masses, since there 

 are many unbroken bubbles which can be examined. On older egg 

 masses, however, where the spumaline has been worn away by weather- 

 ing or eaten away by the caterpillars as they hatched, the best way to 

 observe the specks is to look for small unbroken bubbles between the 

 eggs. The edge of the bubble where it adheres to the egg should be 

 examined as the light-colored egg provides a contrasting background, 

 and the specks are most concentrated in the thickened areas where the 

 bubbles adhere to the eggs or to each other. 



Tests with various organic, inorganic, and enzymatic reagents have 

 established that the specks are an organic substance which is probably 

 the same material as the rest of the spumaline and only distinguishable 

 by its darker color. It is not known why the pigment should concentrate 

 into specks like this and whether or not it has a function, but the specks 

 are present in the spumaline while it is still in the reservoirs of the acces- 

 sory glands before the eggs are laid, so they are not the result of some 

 reaction which takes place after the spumaline has been deposited. 



This means that the presence or absence of specks in a given popula- 

 tion can be checked by one of two methods: either by examination 



