While this interpretation has been challenged by Grimaldi and Engel (2005) as being perhaps attributable to mites, repeated by others (Nel et al., 2007), there are significant factual problems with asserting a mite as a causal agent, as mites are an order-of-magnitude smaller in size, even during the Pennsylvanian, and all of the internal features of the gall, including barrel-shaped coprolites,
mandibulate bite marks, exit hole plugs, and nutritive tissue formation in the host plant strongly suggest a holometabolan galler (Labandeira and Phillips, 1996, 2002).
Moreover, interspecific competition occurred far more frequently between sap-feeding species such as aphids and scale insects than between
mandibulate folivores like lepidopterans and beetles, a finding which has been previously reported (Lawton and Strong 1981, Karban 1986, Denno and Roderick 1992).