The long-tongued nectar thief

There’s a famous story about a very long, skinny flower.

In Madagascar, there is an orchid in which the nectar is about 30 centimeters away from the opening of the flower. When examples of these flowers arrived at Charles Darwin’s doorstep in 1862, he knew that most orchids in this group were pollinated by moths. But there was no known moth that was big enough to do so.

Later that year, in a book on flower pollination, Darwin wrote, “in Madagascar there must be moths with proboscises capable of extension to a length of between ten and eleven inches!’ In other words, Darwin predicted a giant moth.

Okay, a moth with a giant tongue, if you want to be precise about it.

Darwin didn’t live to find out if he was correct. He died in 1882, but a moth was found in 1903 that had a long enough tongue, and his prediction was considered confirmed.

That story has strongly influenced how people view specialized flowers: that anything that evolves the necessary machinery to exploit the flower must be in a relationship that benefits both the flower and the animal.

A new paper by Bauder and colleagues looks at a wonderful butterfly, Eurybia lycisca. Check out this beauty:

Lovely blue! And look at that tongue! The tongue is about twice as long as the body of the butterfly!

The authors in the paper are looking at Calathea crotalifera, and they looked at the behaviour of the butterfly around the flower. They were able to show that the butterfly was able to get nectar from the flower, but they never saw a butterfly lifting any pollen from the flower. And if the butterfly doesn’t get any pollen, there’s no way it can transfer pollen from one flower to another.

That busted the idea that this butterfly and this flower had co-evolved. The butterfly is stealing the nectar rather than the traditional tit-for-tat we think of with insects visiting flowers, where “we both get what we want.”

What does pollinate this flower? Bees, as it turns out. The authors don’t describe the behaviour of the bees closely, but I expect that they bees are smaller and crawling down into the flower in a way that the butterfly can’t.

It’s also mentioned in the discussion that the caterpillars of this species also feed on the leaves of this species. Based on this, you might expect that this flower is in an arms race with this butterfly. It would be interesting to see if the butterflies are exerting selection pressure on the flowers for longer corrola tubes or some other sort of chemical defense.

Reference

Bauder J, Lieskonig N, Krenn H. 2010. The extremely long-tongued Neotropical butterfly Eurybia lycisca (Riodinidae): Proboscis morphology and flower handling Arthropod Structure & Development: in press. DOI: 10.1016/j.asd.2010.11.002

Kritsky G. 1991. Darwin's Madagascan hawk moth prediction. American Entomologist 37(4): 206-210. http://www.ingentaconnect.com/content/esa/ae/1991/00000037/00000004/art00006 PDF