For a plant to be considered carnivorous, a key criterion is that experimental manipulations of its insect food supply can be shown to produce growth or developmental responses. Increases in size and biomass have been shown for Pinguicula
supplemented with appropriate animal bodies 
, a result that was not duplicated here.
The dominant pattern in Dipsacus
biomass was attributable to the natural variation between sites, initially manifest as differences in the sizes of over-wintering rosettes and probably explicable by unquantified differences in soil chemistry. The correlation between number of rosette leaves and final biomass was highly significant (r
0.84, p<0.01), agreeing with the model that the plant's final size is largely determined by energy capture in the previous growing season 
. Surprisingly, cutting each leaf base to prevent water buildup had no effect on any growth parameter. Insect nutrition had no detectable effect on biomass, either in absolute terms or as deviation from size predicted from its over-wintering rosette. However, the seed production and the seed mass:biomass ratio differed between insect-feeding treatments increasing as expected if insects were supplying mineral nutrition (). Similarly, Thum 
listed increased seedset along with other indices of overall size when Drosera
were fed supplemental flies (although based on a pseudo-replicated design). Wakefield 
found that supplemental feeding of Sarracenia
with flies did not increase size or biomass but did increase their nutrient content: in this case seed set was not quantified. Meyers 
reported Utricularia's growth is reduced by half in the absence of prey, but again seedset was not quantified.
These data allow an estimate of nitrogen fluxes. The total animal biomass added over the season was 0.33 g dry mass per plant; assuming diptera have a mean nitrogen content at 10% 
this equates to approximately 33 mg nitrogen as animal tissue added to a plant over the season. It has not been possible to find a published value for the nitrogen content of Dipsacus
seeds, but Mattson 
gives a range of 1–6% for seeds in general with lower values for non-legumes. Even assuming a low value of 15 mg/g nitrogen in seeds, the supplemental feeding supplied enough nitrogen for less than 2.5 g of seeds, while the regression lines predicted a difference between fed and control plants' seedset of approximately 7 g for a 300 g plant (), implying that the apparent seed gain involved more nitrogen than was added in food. This may be from some other nutrient being limiting, or a statistical artefact; either way the result needs duplicating.
These results provide the first empirical evidence for Dipsacus displaying one of the principal criteria for carnivory given by Juniper et al (3); the use of products absorbed from prey to increase fitness. The result needs to be duplicated, and there remain other criteria of carnivory still to be demonstrated in Dipsacus; does it actively attract insects to its basins, how are insects digested / broken down, and are there any specialist structures such as waxy scales which cause insects to slip?