Monday, October 31, 2011

Don't Eat Me, I Don’t Taste Good

I recently attended a meeting of our local field naturalist society where the speaker lectured on the strategies some animals (mostly insects) adopt to avoid being eaten by predators.
Research indicates that effective strategies can involve unpalatability, toxicity, the use of warning colours, markings and startling movement. While not a lot of research has yet been done, some of our long-held beliefs are already being exposed as myths.

Adult Monarch Butterfly

One defense is thought to be “mimicry”, where a palatable insect “mimics” the appearance of an unpalatable one. Likely the best known example is of the Viceroy and Monarch butterflies.
Monarch larvae feed on milkweed plants which are toxic and the larvae are said to become distasteful to predatory birds and small animals.
Viceroy butterflies very closely mimic Monarchs and for a long time have been thought to be avoided by predators because of that similarity, even if Viceroy larvae don’t eat milkweed.

It’s a great theory. Trouble is, it quite possibly isn’t correct.

Adult Viceroy Butterfly. Note diagnostic dark bar on hind wing.

Recent research indicates that Viceroys may be unappetizing in their own right and their similarity to Monarchs may be no more than coincidence.

So another myth bites the dust.

The bight colouration of Monarch Butterfly larvae is thought to be a warning - "don't eat me, I don't taste good". But this Stink Bug finds Monarch larvae tasty enough. (A Stink Bug's defence against predators may be the foul odour these guys exude when disturbed.)

More interesting to me is how the predators come to know they should avoid certain insects.
Most lepidopterists and many scientists believe it is a learned behavior - a bird grabs a Monarch butterfly and is repelled by the taste. Ever after, that bird avoids both Monarchs and Viceroy butterflies.
But does it really happen that way? Or is this just another fanciful theory without foundation.

Could the explanation be much deeper and more mysterious? Something like inherent fear?

Why not?

Any farmer will tell you how chickens, hatched in an incubator and raised without other adult birds, will demonstrate abject fear at the sight of a predatory bird on the distant horizon. How do the chickens know that bird is a threat?

What about the innate fear of snakes common to many horses?

Toss a length of garden hose into an enclosure with horses and watch the hose be chopped into small pieces in short order.

From where do the chickens and horses get that inherent fear?

There is so much of the natural world we simply don’t understand.

Another protective phenomenon can be deceptive appearance. The following two images of Viceroy larvae resemble nothing more than bird droppings and would likely be ignored by most hungry birds.

My on line stock photo catalogue now has more than 11,000 images like the ones in this newsletter available for use in advertising, publication and on the internet.

Just drop me a line.

Links to some of my butterfly and insect pages:

Link to Monarch Butterfly photos.

Link to Viceroy Butterfly photos.

Link to Monarch Butterfly life cycle photos.

Link to photos of extinct and extirpated butterflies.

Link to selection of butterfly photo galleries.

Link to 32 other selected insect groups.

1 comment:

  1. I often wonder how much information, memory etc is encoded in the DNA. I think that makes scientific and esoteric sense as well! A joy to read your blog, as always.