Science and Mathematics Faculty Publications

Measure up: The impact of various ecological factors on lepidopteran proboscis length

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Feeding adaptations occur in many organisms due to their diets and foraging strategies, impacting the morphological structure of their mouthparts and, ultimately, their survival. Lepidopterans have a mouthpart known as a proboscis and this long, thin, tube-like structure allows butterflies to access nectar from flowers. Previous studies have shown a positive correlation between the corolla length of certain flowers and the proboscis length of the insects that feed from those flowers, demonstrating the benefit of having a longer proboscis to access a wider variety of flowers. Within Lepidoptera, monarch butterflies (Danaus plexippus) are a unique study system because of their multi-generational migration. In the summer, a generation of non-migratory monarchs stays in the northern regions of Eastern North America. In the fall, their offspring migrate southwards to Mexico where they overwinter, and they then remigrate northwards during the following spring. Previous research has already determined morphological differences between migratory and non-migratory monarchs, but it is unknown whether the length of their proboscis is also affected by migratory status. Even though the proboscis is not directly linked to flight, it is still important to consider because it is how migratory monarchs access the nutrients along the way that are needed to sustain such a long flight during migration. Since the length of the proboscis plays such a vital role in lepidopteran feeding and survival, it is important to consider what factors might affect proboscis length. In this study, I measured the proboscises of monarchs and other non-migratory butterflies in Ohio to understand how proboscis length is affected by the following factors: 1) seasonality or migratory status, 2) sex, and 3) developmental conditions and anthropogenic influences. Other butterfly species were included in this study to determine whether any trends found in monarchs also extend to other butterflies, or if they are unique to monarchs and part of their migratory syndrome. To answer these questions, I measured the proboscis lengths of summer and fall monarchs captured over the last five years (2018-2022) and of other butterflies captured during 2022. My results indicate that proboscis length is not part of the monarch migratory syndrome, but it is affected by sex and developmental conditions. These differences in proboscis length between sexes could be the result of differing foraging strategies and energy requirements of male and female monarchs overall. I also found that temperature and light play a role in monarch development, since monarchs that were raised in captivity had shorter proboscises and larger thoraxes than wild-caught monarchs. Additionally, I found no overarching patterns across other lepidopteran species regarding the effect of seasonality, sex, and anthropogenic influences on proboscis length.


Ecomorphology, proboscis length, monarchs, migratory syndrome, Lepidoptera, sexual dimorphism