190 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



Female neustrium can be easily separated from castrensis and franconicum 

 by the length of the antennal rami. At a point halfway to the antennal 

 tip, the rami oi neustrium are approximately twice as long as the diameter 

 of the flagellar segment from which they arise (fig. 55) ; those of castrensis 

 andfranconicum are approximately as long as the diameter of the flagellar 

 segment from which they arise (fig. 56). No good characters for sepa- 

 rating female castrensis from franconicum were found except for differences 

 in the wing scales. Two basic kinds of scales are present on the wings of 

 both species — long, hairlike ones and flattened, shinglelike ones. 

 Both kinds are numerous on the wings of castrensis, and they completely 

 obscure the wing membrane. On the wings oi franconicum both kinds 

 of scales are smaller and less numerous except cilong the veins, and the 

 wing membrane is easily visible between the scales, especially near the 

 center of the wing. This makes it appear somewhat transparent. In 

 addition, many of the shinglelike scales are less heavily pigmented 

 and stand at right angles to the wing membrane on franconicum, thereby 

 increasing the transparency of the wing. These characteristics are even 

 more striking in male franconicum. 



From this short summary of differentiating characteristics and basic 

 similarities, it can be seen that these three Palearctic species form a 

 group of species which are more closely related to each other than any 

 of them is to any of the North American species. This is particularly 

 evident when it is pointed out that all three lay helical egg masses and 

 build large tents — a combination that is not found in any North 

 American species. In addition, the ovipositors of females are similar, 

 but difierent from any North American species, and the male terminalia 

 are more similar to each other than to any of the North American 

 males. Perhaps M. neustrium is closest to tlie North American M. 

 disstria, and M. castrensis and M. franconicum are closest to the North 

 American M. tigris, but they are still very distant. 



The Relationships Between the North American 



Species 



When everything is considered, the North American species fall into 

 two groups. One group is made up of disstria, tigris, and constrictum. 

 The most important similarities are that all three lay helical egg masses, 

 build little or nothing in the way of a tent, have their forewings crossed 

 by lines which are darker than the background color, and have females 

 with relatively small ovipositors. Within this group disstria is alone in 

 building no tent at all, having a large, distinctive epiphysis (especially 



