24 AMERICAN HYMENOPTERA. 



common and widely distributed. This is probably due to 

 the crepuscular or nocturnal habits of the majority. O. bifo- 

 veolatus is an exception, but the others, so far as known, fly 

 at night or in the evening and are often attracted to light. 

 The adults appear in early spring, and have been taken in 

 Massachusetts from early April till late October, but are most 

 abundant in June, July and August. The date of emergence 

 will probably be earlier for tropical countries, but so far as 

 known the winter is passed in the larval or pupal state. The 

 cocoons are about half an inch long by a quarter of an inch 

 thick in the middle, slightly flattened, oval in shape, com- 

 posed of brownish silk, sometimes darker towards the ends. 

 The habits probably differ little from those of other mem- 

 bers of the tribe which are treated on page 14. 



Economic Importance- 

 The economic importance of this genus can not be esti- 

 mated, for our knowledge of their hosts is too limited, but 

 so far as known they are, with one exception, restricted to 

 Lepidoptera. O. luteus — a European form — has a host list 

 of twenty-nine or more insects, and there is no reason why 

 the American species, especially such a widely distributed 

 form as O. bilineatus, should be more restricted. O. bifo- 

 veolatus forms a noteworthy departure from the other mem- 

 bers of the tribe, and apparently preys entirely upon white 

 grubs — the larvae of Lachnosterna hisca and perhaps other 

 species of this genus. Prof. F. M. Webster records having 

 observed an insect resembling an Ophion ovipositing in the 

 larva of a sawfly — Nematus sp. — but there is doubt as to the 

 identity of the parasite, and this would be the only known 

 case of an Ophionine parasitizing a hymenopteron. 



Variation. 

 The members of this genus show no striking variation in 

 structure or color, and several of the species are so closely 

 related that it is only after careful study that they can be 

 separated. The shape of the discocubital cell and character 

 of the surface of the metathorax show in some species con- 

 siderable variation. The discocubital vein is normally angu- 



