Most butterflies and moths consume liquids using a proboscis, which is a conduit composed of different structures. The purpose of this study was to determine if proboscis structures of Painted lady butterflies (Vanessa cardui) show allometric growth relationships with body weights and proboscis lengths. We hypothesized that potential differences in structural configurations might affect fluid uptake rates. To test this, we fed larvae different treatments of artificial diet to prompt size differences in adults. We measured six proboscis characters and used the allometric growth equation. There was a significant allometric relationship among the measured characters and body weight and proboscis length; however, there was a lack of significance when fluid uptake rate was considered the dependent variable of measured characters, even though trends indicated positive allometry. Our results indicate the presence of allometric relationships in proboscis structures; however, these changes do not greatly influence fluid uptake rates.