484 
Saw-flies, Gall-flies, Ichneumons, 
in a loop over her back, with its tip on the bark of the tree, she makes a der¬ 
rick out of her body, and proceeds with great skill and precision to drill a 
hole into the tree. When the Tremex-burrow is reached she deposits an 
egg in it. The larva that hatches from 
this egg creeps along this burrow until 
it reaches its victim, and then fastens itself 
to the horntail larva, which it destroys 
by sucking its blood. The larva of Tha- 
lessa when full-grown changes to a pupa 
within the burrow of its host, and the 
adult gnaws a hole out through the bark 
if it does not find a hole already made by 
the Tremex. Sometimes the adult Tha- 
lessa, like the adult Tremex, gets her 
ovipositor wedged in the wood so tightly 
Fig. 682. 
Fig. 681 .—Thalessa sp., ichneumon-parasite of the pigeon-tremex. (After Jordan and 
Kellogg; natural size.) 
Fig. 682 .—Thalessa lunator drilling a hole in a tree-trunk, in order to deposit its egg in 
burrow of the pigeon-tremex. (After Comstock; natural size.) 
that it holds her a prisoner until she dies.” 
Another curious large parasitic Hymenopteron is Pelecinus polyturator 
(Figs. 683 and 684), the single American representative of the family Pele- 
cinidae, of whose habits little is known, but which has attracted much atten¬ 
tion because of the strange discrepancy in size between male and female. 
The abdomen of the female is slender and ij inches or more in length, while 
