Hie Progress of the Hessian Fly. 
447 
of a fourth of an inch. It is black, with yellow colourings on 
the tibiae, tarsi, and antenna^. There is a dark-green metallic 
tinge upon the head and thorax. The wings are fringed ; the 
veins of the wings are distinct, and dark brown in colour. 
According to the careful comparative description of Lindeman 
of this insect with the Russian species, termed by him Merisus 
inter medius, there are clear differences of colour and specific 
difference in the antennae of the two species.* 
rig. I. — Semiotellus (Merisus) destructor. Say. 
Insccl magnified. Lines sliowing natural size. 
Professor Riley describes four other kinds of parasites upon 
the Hessian Fly in America. Of these the most important is the 
Platygaster Herrickii, shown in Fig. II. (p. 448), whose method 
of attack is different from that of the Semiotellus, inasmuch as it 
deposits its eggs within the eggs of the Hessian Fly. Packard 
remarks upon this, and quotes Herrick's account of the process. 
" I first saw it, September 23, 1833, in the act of depositing its 
eggs in the eggs of the Hessian Fly. From subsequent observa- 
tion it appears that five or six eggs are laid in a single egg of the 
Hessian Fly. The latter egg hatches, and the animal advances 
to the pupa state as usual, but from the puparium no Hessian 
Fly comes forth." f Professor Riley, it is fair to say, does not 
accept this without verification. 
The Platygaster Herrickii is about the same size as the 
Semiotellus, shining black in colour, with brown tibiae and tarsi. 
The wings are fringed but have no venation. 
Dr. Lindeman has found a species of Platygaster in Russia, 
named by him Platygaster minutus. It is smaller than Platy- 
gaster Herrickii, and has yellow tarsi and tibiae, and does not 
lay its eggs in the eggs, but in the larvae of the Hessian Fly.f 
* ' Die Ptcromaliucn iler Ilesseu Flicgc,' von Professor K. Lindeman. 18SG. 
t Op. cit. 
