Some birds find food by opening stems of herbaceous plants.
So much possibility
Yes there is, yes there is... --Anonymous
It's hard to call it a "dead stem" when it's so full of life. --MJ Hatfield
Driving along Iowa's state highway 9 a while ago, I found my eye caught by contrast: a little patch of lightness on an otherwise rather dark wooded slope.
A pileated woodpecker tree -- one of those recently dead snags all torn up by the Upper Midwest's "Lord God bird" -- is a common enough sight around here...but this one seemed to be on a whole 'nother level.
That bird wasn't messing around!
People say pileated woodpeckers eat mostly carpenter ants, which may be true, but I've noticed they also seem to have a penchant for trees inhabited by wood-boring horntail wasps and their parasitoids, the giant ichneumons. Here's my friend and collaborator MJ Hatfield, deftly showing off these and other insects in a pileated woodpecker tree from her backyard.
Smaller woodpeckers leave sign on trees that's less drastic but no less interesting. This "woodpecker flute" has been in my natural-things collection ever since I found it on the campus of my alma mater, St. Olaf College.
Not long after I collected the "flute" I sawed off a centimeter or so on both ends to make them flat. As you can see, this also emphasized the fact that the twig -- collected from a pine tree -- is hollow all the way through. Presumably an insect (some wood-boring beetle?) hollowed it out or lived inside a pre-existing hollow in the twig. I don't know exactly which type of insect, but clearly -- judging from the amount of effort involved -- the bird really wanted that bug.
Though it's not as widely recognized, some birds are also adept at locating insects hidden within the stems of herbaceous (non-woody) plants. The classic North American example is a downy woodpecker or black-capped chickadee opening up a goldenrod gall, which contains a fly larva. (Links take you to images of the birds at work on this task.) But there are other examples, too. In this two-part post, we'll explore a handful of obscure but fascinating associations between bird, insect, and herb.
JEWELWEED
With mesmerizing orange or yellow flowers (depending on species), and droplets of rain or dew beading readily on its leaves, jewelweed (Impatiens spp.) may entrance you. In winter its dead stems are less likely to impress, but their unique pinkish or rusty color and weak knobby "joints" are still distinctive.
Inspecting such patches, you may find this:
Note the ragged, rough appearance of these holes, suggesting they were made after the plant had dried down to its currently brittle state (rather than while the plant was still succulent and green). It took me only a few minutes of searching this jewelweed colony on my friends' property (thanks, Lindy and Lee!) to find several more examples. Look carefully, and you'll see at least one hole gouged in each stem piece in these images.
Though I've not yet had the privilege of watching it happen, I believe these stems were raided by birds -- for the purpose of harvesting a particular type of insect. A mouse or other rodent could perhaps have left this sign, but to me, the small size and splintered appearance of the holes indicate they were made by a sharp, narrow object (a bird's bill or beak). A predatory wasp might hypothetically chew into a stem to harvest insects inside, but its tiny mandibles should leave a much more delicately fashioned opening.
Assuming for now that this is a bird, what exactly is it looking for? In my experience, herbaceous stems are not indiscriminately opened by birds hoping by dumb luck to find tasty things inside. Rather, birds -- being the smart bunch that they are -- have learned to recognize and exploit specific associations between plants and insects. In this case, the target is a caterpillar -- the larva of a certain species of moth (order Lepidoptera). Larvae of this moth species overwinter in dead stems of jewelweed, apparently emerging as adult moths sometime in spring. (I've tried to rear them to adulthood but haven't succeeded, so the species is unidentified as yet.)
These larvae are actually rather easy to find inside jewelweed stems at this time of year. Try finding them yourself! (Caveat: I haven't yet learned to tell the jewelweed species apart from their dead stems, so I'm unsure if it's both of our commonly encountered Impatiens species, or just one of them, that plays host to the larvae.)
FIGWORT
Plants in the genus Scrophularia, commonly called figworts, are related to garden snapdragons. In fact, their plant family is known as Scrophulariaceae (say it with me! Skroff - you - lair - ee - AY - cee - ee), which, while cumbersome, shows the importance figwort held to the people who named the family. It's a surprise, then, that figwort is not better known. I'll leave it to a couple of North America's great wildflower websites -- both Midwestern, by the way -- to help you recognize Scrophularia marilandica and S. lanceolata, which (I think) can both be found here in northeastern Iowa. Let's get to the bird damage!
And, inside a figwort stem* not yet raided by birds:
This insect species, once again in the form of a caterpillar that will one day be an adult moth, has been dubbed the "verbena bud moth" (scientific name: Endothenia hebesana). It's an extreme generalist, known to feed on many different plant species.** Biologists refer to this habit as polyphagy, loosely translated as "many eater" or "varied eater."
However, just because this bug is flexitarian does not mean its relationships with plants are haphazard. You can reliably find its larvae in stems of certain species of plants (and not others) at certain times of year -- which means the birds can, too. That deserves emphasis: Even polyphagous insects may establish patterns of association with particular plant hosts -- and birds, humans, and anyone else who's interested can learn to recognize these patterns.
Consider a human analogy. You may be willing to visit just about any c-store, diner, or coffee shop to get your daily caffeine buzz, but you probably have just a few places you prefer to go, and you probably go there at certain times and order certain drinks. An undercover cop trailing you to document your nefarious coffee-drinking could learn your top haunts and favorite brews easily enough. Same idea with our ecological example: Figwort stems in winter are one of this insect's preferred places...and the birds have found out!
---
If you're a caterpillar of the verbena bud moth who makes it safely through the winter inside a figwort stem, you'll most likely make a cocoon there, in which you will shed your final larval "skin" (exoskeleton) and become a pupa. In the pupal stage, you wear a unique skin that looks a bit like a caterpillar, a bit like an adult, but not exactly like either. Beneath this skin, much of your body is more or less dissolved and rearranged into a nearly-adult moth-to-be. When you're ready, you thrust yourself out of the stem, break your pupal skin, and emerge as a newly minted, scale-winged flying creature. (Lepidoptera, or "scale wing," refers to the microscopic scales that slough off the wings like dust when you handle an adult moth or butterfly.)
Finally an adult, you now get to wear a sort of gray-green camo on your brand new wings, and two little fireburst ornaments of rusty orange on your back. Pretty cool!
---
In part 2 we'll examine two bird-plant-insect connections involving the plants cow parsnip (Heracleum maximum) and wild lettuce (Lactuca spp.).
A smart bunch, part 2
---
NOTES
* You may notice that, aside from the color differences, there's at least a passing resemblance between the larvae in jewelweed and figwort. Indeed, it's possible the jewelweed moth larva may turn out to be Endothenia hebesana, too. The easiest way to tell is to raise the larva to adulthood.
** If you go checking figwort stems for evidence of bird damage, you should know that verbena bud moth larvae actually make holes in figwort stems too. However, they do this as part of their routine stem-dwelling activities, and their holes are quite different from those made by birds. I've documented a larva-made stem hole and its architect here, on Bugguide.
So much possibility
Yes there is, yes there is... --Anonymous
It's hard to call it a "dead stem" when it's so full of life. --MJ Hatfield
Driving along Iowa's state highway 9 a while ago, I found my eye caught by contrast: a little patch of lightness on an otherwise rather dark wooded slope.
A pileated woodpecker tree -- one of those recently dead snags all torn up by the Upper Midwest's "Lord God bird" -- is a common enough sight around here...but this one seemed to be on a whole 'nother level.
People say pileated woodpeckers eat mostly carpenter ants, which may be true, but I've noticed they also seem to have a penchant for trees inhabited by wood-boring horntail wasps and their parasitoids, the giant ichneumons. Here's my friend and collaborator MJ Hatfield, deftly showing off these and other insects in a pileated woodpecker tree from her backyard.
Smaller woodpeckers leave sign on trees that's less drastic but no less interesting. This "woodpecker flute" has been in my natural-things collection ever since I found it on the campus of my alma mater, St. Olaf College.
Though it's not as widely recognized, some birds are also adept at locating insects hidden within the stems of herbaceous (non-woody) plants. The classic North American example is a downy woodpecker or black-capped chickadee opening up a goldenrod gall, which contains a fly larva. (Links take you to images of the birds at work on this task.) But there are other examples, too. In this two-part post, we'll explore a handful of obscure but fascinating associations between bird, insect, and herb.
JEWELWEED
With mesmerizing orange or yellow flowers (depending on species), and droplets of rain or dew beading readily on its leaves, jewelweed (Impatiens spp.) may entrance you. In winter its dead stems are less likely to impress, but their unique pinkish or rusty color and weak knobby "joints" are still distinctive.
Inspecting such patches, you may find this:
Note the ragged, rough appearance of these holes, suggesting they were made after the plant had dried down to its currently brittle state (rather than while the plant was still succulent and green). It took me only a few minutes of searching this jewelweed colony on my friends' property (thanks, Lindy and Lee!) to find several more examples. Look carefully, and you'll see at least one hole gouged in each stem piece in these images.
Though I've not yet had the privilege of watching it happen, I believe these stems were raided by birds -- for the purpose of harvesting a particular type of insect. A mouse or other rodent could perhaps have left this sign, but to me, the small size and splintered appearance of the holes indicate they were made by a sharp, narrow object (a bird's bill or beak). A predatory wasp might hypothetically chew into a stem to harvest insects inside, but its tiny mandibles should leave a much more delicately fashioned opening.
Assuming for now that this is a bird, what exactly is it looking for? In my experience, herbaceous stems are not indiscriminately opened by birds hoping by dumb luck to find tasty things inside. Rather, birds -- being the smart bunch that they are -- have learned to recognize and exploit specific associations between plants and insects. In this case, the target is a caterpillar -- the larva of a certain species of moth (order Lepidoptera). Larvae of this moth species overwinter in dead stems of jewelweed, apparently emerging as adult moths sometime in spring. (I've tried to rear them to adulthood but haven't succeeded, so the species is unidentified as yet.)
These larvae are actually rather easy to find inside jewelweed stems at this time of year. Try finding them yourself! (Caveat: I haven't yet learned to tell the jewelweed species apart from their dead stems, so I'm unsure if it's both of our commonly encountered Impatiens species, or just one of them, that plays host to the larvae.)
FIGWORT
Plants in the genus Scrophularia, commonly called figworts, are related to garden snapdragons. In fact, their plant family is known as Scrophulariaceae (say it with me! Skroff - you - lair - ee - AY - cee - ee), which, while cumbersome, shows the importance figwort held to the people who named the family. It's a surprise, then, that figwort is not better known. I'll leave it to a couple of North America's great wildflower websites -- both Midwestern, by the way -- to help you recognize Scrophularia marilandica and S. lanceolata, which (I think) can both be found here in northeastern Iowa. Let's get to the bird damage!
And, inside a figwort stem* not yet raided by birds:
This insect species, once again in the form of a caterpillar that will one day be an adult moth, has been dubbed the "verbena bud moth" (scientific name: Endothenia hebesana). It's an extreme generalist, known to feed on many different plant species.** Biologists refer to this habit as polyphagy, loosely translated as "many eater" or "varied eater."
However, just because this bug is flexitarian does not mean its relationships with plants are haphazard. You can reliably find its larvae in stems of certain species of plants (and not others) at certain times of year -- which means the birds can, too. That deserves emphasis: Even polyphagous insects may establish patterns of association with particular plant hosts -- and birds, humans, and anyone else who's interested can learn to recognize these patterns.
Consider a human analogy. You may be willing to visit just about any c-store, diner, or coffee shop to get your daily caffeine buzz, but you probably have just a few places you prefer to go, and you probably go there at certain times and order certain drinks. An undercover cop trailing you to document your nefarious coffee-drinking could learn your top haunts and favorite brews easily enough. Same idea with our ecological example: Figwort stems in winter are one of this insect's preferred places...and the birds have found out!
---
If you're a caterpillar of the verbena bud moth who makes it safely through the winter inside a figwort stem, you'll most likely make a cocoon there, in which you will shed your final larval "skin" (exoskeleton) and become a pupa. In the pupal stage, you wear a unique skin that looks a bit like a caterpillar, a bit like an adult, but not exactly like either. Beneath this skin, much of your body is more or less dissolved and rearranged into a nearly-adult moth-to-be. When you're ready, you thrust yourself out of the stem, break your pupal skin, and emerge as a newly minted, scale-winged flying creature. (Lepidoptera, or "scale wing," refers to the microscopic scales that slough off the wings like dust when you handle an adult moth or butterfly.)
Finally an adult, you now get to wear a sort of gray-green camo on your brand new wings, and two little fireburst ornaments of rusty orange on your back. Pretty cool!
---
In part 2 we'll examine two bird-plant-insect connections involving the plants cow parsnip (Heracleum maximum) and wild lettuce (Lactuca spp.).
A smart bunch, part 2
---
NOTES
* You may notice that, aside from the color differences, there's at least a passing resemblance between the larvae in jewelweed and figwort. Indeed, it's possible the jewelweed moth larva may turn out to be Endothenia hebesana, too. The easiest way to tell is to raise the larva to adulthood.
** If you go checking figwort stems for evidence of bird damage, you should know that verbena bud moth larvae actually make holes in figwort stems too. However, they do this as part of their routine stem-dwelling activities, and their holes are quite different from those made by birds. I've documented a larva-made stem hole and its architect here, on Bugguide.
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