There’s an old adage that the higher you climb in elevation, the darker your fly should be. Why would this be? Is there any credibility to this claim? Actually, there is! Detailed in M.S. Mani’s 1968 publication on high alpine insects, darker body pigmentation increases with elevation, known as “high altitude melanism”. The higher you climb, the more melanin produced, and dark body pigmentation is a pronounced trait in almost all high alpine insects. The higher you climb, the darker a bug’s coloration. But that doesn’t just mean black. Browns, reds, oranges, and even deep yellows can be common. Spots or banding patterns also darken compared to insects from lower elevation meadows.
Evolutionary Advantages
Why would insects want to be darker at high elevations? Well, regardless of the exact color, these prominent colors compliment blues, effective for absorbing and neutralizing high intensity light, common as atmosphere thins at high altitudes (Harris et al. 2013). Without a thick overhead atmosphere, damage from UV light can pose greater risks at high elevations compared to lowlands. Over time, insects have developed strategies to ward off the threats of high energy UV light. The production of melanin darkening insects acts like an electrical ground to dissipate the dangers of high UV light. Further, darker colors can help warm up these cold blooded insects during the short alpine summer.
Figure from Kohler et al, 2017 showing darker brown grasshoppers found at higher elevations, while the same grasshoppers take on a greener coloration at lower elevations.
This example highlights the altitudinal groupings of body color for meadow hoppers. Researchers noted how altitude leads to changes in meadow hopper colorations, and was present in males and females. This suggests that the brown coloration helps thermoregulate at high altitudes (Kohler et al, 2017).
Angler Strategies
You don’t need to overhaul your flow box for that next alpine outing. Simply make sure to include some dark variants of Elk Hair Caddis, Hippy Stompers, Humpies and Parachute Ants. Royal Wulffs and other flies with peacock herl should work well too. I always carry too much and would still bring some light colored flies just in case, but they shouldn’t take up too much room.
If fish get picky, color might be an important factor to consider for alpine fly selection.
Sources:
Mani, M.S. 1968. Chapter 3: Ecological Specializations of High Altitude Insects In Ecology and Biogeography of High Altitude Insects. Series Entomologica. 4.
Harris, R., McQuillan, P., & Hughes, L. 2013. A Test of the Thermal Melanism Hypothesis in the Wingless Grasshopper Phaulacridium vittatum. J Insect Sci. 13:51. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3740933/
Kohler, G., Samietz, J., Schielzeth, H. 2017. Morphological and colour morph clines along an altitudinal gradient in the meadow grasshopper Pseudochorthippus parallelus. PLoS One. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0189815
Author Bio:
Andy Witt, scientist and angler obsessed with chasing and understanding all gamefish, writes on the intersection of science, conservation, and fly fishing for Due West Anglers, based out of Denver, CO.
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