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Hello Chris! The corps-feeding in Tabanidae is well known phenomenon, at least it's role in the mechanical transmission of tularemia and antrax. For those who interested I can recommend to search in the old soviet scientific papers (but I'm afraid the knowledge of russian language is prerequisite for doing so :P, although some english abstracts could be found across the web, e.g. http://www.cabdirect.org/abstracts/19432700638.html;jsessionid=C29BCCBF025A5AFC7BB774046F1D0077 ).
In short, this issue is reviewed in the Olsufjev's fundamental work- Olsufjev, N.G. - 1977- Horse flies. Family Tabanidae. -In Fauna SSSR. - Zoological Institut, Academy of Sciences of the USSR, Insecta, Diptera New Series, No.113, Vol.7, part 2, 436 pp. [In Russian].
By the way, nice photos! It's very nice and important to have such an illustrations.