J. H. MERRILL 139 



least soft. As the borer enters, the sheaths make a larger and 

 larger loop on one side of the body, or even a valve on each side. 

 . . . In withdrawing the ovipositor the reverse action takes 

 place and the loops of the outer sheaths gradually become 

 smaller and smaller; the ovipositor is again forced back into the 

 tough bladder-like membrane between the sixth and seventh 

 joints dorsally and we have a repetition of the appearance." 



The old idea was that the Megarhyssa probed a burrow with 

 her ovipositor until she came in contact with the larva of a 

 Tremex, which she pierced and deposited an egg therein. The 

 observation has also been made that the insect is lignivorous and 

 not parasitic. Both of these conclusions have been shown to 

 be false. Riley quotes J. A. Lintner,^'' as follows: 



". . . In all instances wdiere I have found the female 

 depositing, it has been in trees infested with Tremex columha, 

 and I have found her more numerous on badly affected or injured 

 trees, or even on stumps or broken trunks already partly decayed. 

 The instinct to reach the egg or larva of Tremex, so dwelt upon 

 in popular accounts, is imaginary. She bores directly through 

 the outer parts of the tree, and doubtless probes for a burrow; 

 but her egg is consigned anywhere in the burrow; the young larva 

 seeks its prey, and lives and develops without penetrating the 

 body of its victim, but fastened to the exterior. This habit 

 among parasites is much more common than is generally sup- 

 posed. A great many Rhyssa (i. e. Megarhyssa) larvae doubtless 

 perish without finding food, and a great many females die in 

 probing for a burrow, especially when they burrow through wood 

 that is sound and hard. " 



In this same paper, Riley in speaking of some personal observa- 

 tions, says, ''. . . We examined the burrows very carefully 

 and found Thalessa (i. e. Megarhyssa) in all stages at that time — 

 larvae, pupae of both sexes, and imagines of both sexes within 

 the tree — the larvae being of various sizes and invariably external 

 to the Tremex: i. e. not within, but holding on to its victim and 

 sucking the latter's life away, without in any case entering the 

 body." 



The insect remains within the tree until it becomes adult, then 

 it gnaws its way to the surface and escapes. The males usually 



" Country Gentleman, xlix, 1S84, p. 331. 



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TRANS. AM. ENT. SOC, XLI. 



