The distinctive orange and black wings of monarchs (Danaus plexippus) have long been known to advertise their bitter taste and toxicity to potential predators. Recent work also showed that both the orange and black coloration of this species can vary in response to individual-level and environmental factors. Here we examine the relationship between wing color and flight performance in captive-reared monarchs using a tethered flight mill apparatus to quantify butterfly flight speed, duration and distance. In three different experiments (totaling 121 individuals) we used image analysis to measure body size and four wing traits among newly-emerged butterflies prior to flight trials: wing area, aspect ratio (length/width), melanism, and orange hue. Results showed that monarchs with darker orange (approaching red) wings flew longer distances than those with lighter orange wings in analyses that controlled for sex and other morphometric traits. This finding is consistent with past work showing that among wild monarchs, those sampled during the fall migration are darker in hue (redder) than non-migratory monarchs. Together, these results suggest that pigment deposition onto wing scales during metamorphosis could be linked with traits that influence flight, such as thorax muscle size, energy storage or metabolism. Our results reinforce an association between wing color and flight performance in insects that is suggested by past studies of wing melansim and seasonal polyphenism, and provide an important starting point for work focused on mechanistic links between insect movement and color.

Members of the public have long had a fascination with the monarch butterfly,Danaus plexippus, because of its amazing long-distance migration to overwintering sites in central Mexico, and many participate in online citizen-science programs where they report observations of its life history in North America. Here, we examine a little-studied aspect of monarch biology, the degree of overwintering in the southern United States. We compiled 9 years of sightings of overwintering monarchs in the southern United States that were reported to Journey North, a web-based citizen science program, to map the distribution of areas where monarchs are capable of surviving during the winter (i.e., in January and February), differentiating between adult sightings and sightings of breeding activity. We also statistically compared the latitudes of adult and breeding sightings, examined differences across years in latitude of sightings, and quantified the number of monarchs reported with each sighting. Of all 254 sightings, 80% came from Florida and Texas, with the remainder coming from South Carolina, Louisiana, Georgia, Alabama, Mississippi, North Carolina, and even one in Virginia. This distribution was generally consistent with the winter range predicted by prior investigators based on climatic conditions of this region. Sightings of adults were on average from higher latitudes than reports of breeding activity and there was significant variation across years in the average latitude of all sightings. The majority of sightings (94.2%) were of fewer than 10 adult monarchs per location, and there were no reports of clustering behavior that is typical of monarch overwintering in California and Mexico. The results of this investigation broaden our collective understanding of this stage of the monarch life cycle and, more generally, highlight the value of citizen science programs in advancing science.

Developed countries around the world are criss-crossed with vast networks of roadways. Conservationists have recently focused attention on roadsides as possible locations for establishing pollinator habitat, with the monarch butterfly ( Danaus plexippus ) featuring prominently in such discussions. However, roadsides are inherently loud, which could negatively affect developing larvae. We conducted a series of experiments testing if simulated highway noise stresses monarch larvae, which we gauged by non-destructive monitoring of heart rates. In two replicated experiments, larvae exposed for 2 h experienced a significant increase in heart rate (16 and 17% elevation), indicating they perceive traffic noise as a stressor. Meanwhile, experiments exposing larvae for either 7 or 12 days to continuous traffic noise both showed no heart rate elevation at the end of larval development, suggesting chronic noise exposure leads to habituation or desensitization. Habituation to stress as larvae may impair reactions to real-world stressors as adults, which could be problematic for a butterfly that undertakes an annual two-month migration that is fraught with dangers. More generally, these results could have far-reaching implications for the billions of insects worldwide that develop near roadways, and argue that further study is needed before promoting roadside habitat for butterfly conservation.