Saturday, May 30, 2015

Lepidopteran Pollinators & the Proboscis

So I've talked about various types of bee pollinator, fly pollinators, and even wind. But I haven't talked much about Lepidopterans (butterflies).

Today, while out enjoying the weather in the wooded portion of the Notre-Dame-des-Neiges cemetery, I encountered a couple of common butterflies that, unusually, held still long enough for me to photograph them, so I'm going to take my opportunity to talk a little bit about this group of pollinators.

First up, we have the very common Glaucopsyche lygdamus couperi ('Silvery Blue' butterfly), a native of North America with a fairly broad range [1] which you have probably seen before:

Glaucopsyche lygdamus couperi - this individual very obligingly held still for me so I could get a few photos
 Lepidopterans tend to be nectar-feeders, so plants that have co-evolutionary relationships with them will generally produce it in reasonable quantity. They are not as efficient at pollen transfer as bees, as their bodies tend to be lifted up on long legs that prevent the extensive physical contact that we often observe between bee and stamen. Nevertheless, they are valuable and effective pollinators.

Glaucopsyche lygdamus couperi on Vicia cracca (cow vetch) - this is what the underside of the wings looks like
Lepidopterans have one piece of handy equipment that other pollinators do not: a proboscis. The proboscis is a tubular mouthpart that serves essentially as a straw. It varies in length depending on species and, in the case of the longer ones, can be extended or coiled as needed.

So if you're a plant that would benefit from attracting butterflies and excluding other pollinators (perhaps in order to devote your resources to a single, more loyal species rather than take your chances with more fickle visitors), what kind of structure is most suitable? A deep nectar spur (pocket where nectar is produced and stored) that can only be accessed with an insecty straw, of course! So the more exclusively Lepidopteran-pollinated a species, the more likely it is to have a long nectar spur which can only be accessed via proboscis.

I got a fantastic shot of the very common Poanes hobomok ('hobomok skipper' butterfly) using its proboscis to suck up some nectar from Vicia cracca (cow vetch):

Poanes hobomok collecting nectar from Vicia cracca
Poanes hobomok, like G. lygdamus couperi, is native to this region and also very common [2], so it's very likely you've seen one of these before.

Of course, Lepidopterans can and do get nectar from a variety of flowers, many of which aren't specialized exclusively to them, such as Vicia cracca (cow vetch). This introduced species is originally native to Europe which is now broadly distributed in North America (range map here). It is listed as invasive but with low current threat status in Minnesota [3]. Apparently the spread of this species is also leading to a range expansion for the native Lepidopteran G. lygdamus couperi [1].

Vicia cracca
The peas produced by this plant are edible [4] though in my experience not that tasty (starchy, bland).

Vicia cracca
The USDA forest service has a little blurb page about butterfly pollination for those interested. And, a bonus picture:

Poanes hobomok on Vicia cracca

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