Butterflies are nectar feeders and require frequent access to the sugars and amino acids that nectar provides. How do they find the flowers and inflorescences that provide them with nectar, and how do they locate the nectar once they have arrived at a flower?
Butterflies may be specialists, i.e. visiting only one, or a few types of flowers; or generalists, visiting a large number of different nectar sources. Clearly, evolution has had a part to play in this, and species with long proboscises are better adapted to extracting nectar from flowers with long, deep corollas. But there are many exception to this rule, and butterflies with short proboscises still have a go at some of the flowers where nectar is deep and hard to get at!
Butterflies can learn, and learning plays an important role in shaping what flowers they come to prefer and use in order to obtain nectar, even though some preferences are hard-wired (i.e. innate). They learn which flowers provide the best rewards, and use a variety of different cues (or signals) to find a flower, land on it and position themselves in order to extract its nectar.
The smell (floral scent) and colour of a flower are probably the two most important cues that a butterfly uses. For example, Indian red admirals, depend primarily on the colour of a flower, and less on its scent, during visits (Ômura & Honda, 2005). Is this also true for our Red admirals (below) in Europe? I don’t know, but it would be interesting to find out. In other species, floral scents are more important than colours in helping the butterfly find nectar sources.
The size and shape of the flower also affect what a butterfly will visit, and individual species will have preferences and priorities, even if they are generalists. In practice, butterflies will use a variety of cues to obtain what they need.
Exactly how a butterfly knows where to place the tip of its proboscis when it arrives at a flower is a bit of a mystery, but according to Professor Harald W. Krenn, an expert on the proboscis of butterflies, butterflies perform similar flower-visiting behaviour, and the probing movements of their proboscises show a
characteristic pattern. A butterfly usually approaches an inflorescence with a loosely unrolled proboscis (below).
The proboscis is then fully unrolled and bent into a characteristic position, with the first one third of the proboscis held out horizontally, and the remaining two thirds pointing downwards (below).
The shape of the bent, or bend, region – the point of inflection (below) – varies from species to species, depending on the length and proportions of the proboscis (Krenn, 2008).
Butterflies engage in a characteristic series of movements, which allow them to probe flowers for nectar using the tip of their proboscises. This is probably best seen in skippers (below). The movements of the proboscis are mainly up and down; only the tip can be bent from side to side. Typically, according to Krenn (2008), the proboscis is raised up until the tip no longer touches the surface, then the bend region is extended or flexed, thereby moving the tip of the proboscis forward or backwards.
Finally, the proboscis is lowered down towards the nectar source, until the tip makes contact with the flower.
The speed and dexterity with which butterflies maneuver their proboscis is truly amazing. Whether they learn to some extent how to do this, or are completely proficient from the moment they become adults, I don’t know. I expect they get a bit more skilled as they get older!
As always, there is a lot more to this topic than I have covered here, with a vast literature that also relates to other pollinators, such as bees. Nevertheless, there remains, I think, a huge amount more to discover, especially concerning the techniques used by different butterfly species on different flowers. I described a little of the form and function of the butterfly proboscis in a previous blog, but if you are interested in the details I would strongly recommend the papers of Harald W. Krenn, some of which are available via his website, here.
References
Andersson, S. (2003). Foraging responses in the butterflies Inachis io, Aglais urticae (Nymphalidae), and Gonepteryx rhamni (Pieridae) to floral scents. Chemoecology, 13(1), 1-11.
Andersson, S., & Dobson, H. E. (2003). Behavioral foraging responses by the butterfly Heliconius melpomene to Lantana camara floral scent. Journal of chemical ecology, 29(10), 2303-2318.
Goulson, D. (1999). Foraging strategies of insects for gathering nectar and pollen, and implications for plant ecology and evolution. Perspectives in plant ecology, evolution and systematics, 2(2), 185-209.
Krenn, H. W. (2008). Feeding behaviours of neotropical butterflies (Lepidoptera, Papilionoidea). Denisia, zugleich Kataloge der oberösterreichischen Landesmuseen Neue Serie, 88, 295-304.
Ômura, H., & Honda, K. (2005). Priority of color over scent during flower visitation by adult Vanessa indica butterflies. Oecologia, 142(4), 588-596.
Tiple, A. D., Khurad, A. M., & Dennis, R. L. (2009). Adult butterfly feeding–nectar flower associations: constraints of taxonomic affiliation, butterfly, and nectar flower morphology. Journal of Natural History, 43(13-14), 855-884.
Weiss, M. R., & Papaj, D. R. (2003). Colour learning in two behavioural contexts: how much can a butterfly keep in mind?. Animal Behaviour, 65(3), 425-434.
Tang, Y. C., Zhou, C. L., Chen, X. M., & Zheng, H. (2013). Visual and olfactory responses of seven butterfly species during foraging. Journal of insect behavior, 26(3), 387-401.
What a fascinating order. I’ve already visited Krenn’s website. A true treasure trove. Thank you for sharing.