Take a walk in a winter forest and you can’t help but notice beech trees. Silky smooth bark and sand-colored dry leaves stick out like Christmas lights against a dull and gloomy background. While every other leaf drifted to the forest floor months ago, beech leaves hold tight like cat hair on a sweater.
It’s called marcescence – these leaves that just won’t drop – and it’s common in oak and beech (the trees are close relatives). But why keep the leaves? Are these trees just photosynthetic versions of hoarders?
One possible reason may be to protect that bud, the thin tapered structure often described as “cigar-shaped.” Inside the scaly covering are the beginnings of the new year’s growth. Hungry deer can ruin a tree’s plans for spring. But with beech trees, deer tend to get a mouthful of dry leaves whenever aiming for a yummy bud. (1)
What about attacks from smaller enemies? Insects seem to prefer infesting trees with leaves hanging on over winter. R. Karban decided to yank all the leaves off a few dozen small oaks and compare infestation levels of a tree-noshing wasp. (2) His numbers indicate that wasps prefer leaf-hoarding trees three-to-one compared to his denuded ones.
I believe Nature is constantly sending messages of wisdom if we’ll just listen. In this case, perhaps she’s saying “every action has an upside and downside, but with diversity, there’s always hope for a better future.”
- Svendsen, Claus R. 2001. Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests. Alces 37(2): 475-482.
- Karban, R. 2007. Deciduous leaf drop reduces insect herbivory. Oecologia. 153: 81-88.
Many flowers use insects to transfer pollen from one plant to another. Some flowers attract bees or butterflies. The corpse flower, though, uses carrion beetles and flesh flies. What attracts these pollinators? The color of decaying flesh, putrid scents, and the warm temperature of a freshly dead body. Lovely.
While we humans tend to focus on color, beetles and flies who pollinate the corpse flower may be more attracted to the scent and temperature. Angioy et al. (2004) showed that certain insects have the abilities to “see” temperatures and are attracted to heat. The heat generated by the spadix of the flower is unusual in the plant kingdom. Not many plants expend tons of energy to warm up to around 100 degrees Fahrenheit. Those few that do are called “thermogenic plants.” It’s generally accepted that the heat increases the range of the odors (Barthlott et al. 2009), which is true of course. But wouldn’t all plants benefit by increasing scent ranges? Yet this mechanism is found in plants that only mimic carcasses to attract pollinators – plants like the skunk cabbage and voodoo lily.
While most flowers give their pollinators a reward of some kind (think nectar), the corpse flower seems to just take, take, take. The plant mimics carrion, where pollinators normally lay their eggs, yet gives the pollinators no food or reward. Or could it?
I personally found it interesting that the spathe of the corpse flower closed back up after it bloomed. It’s probably protecting the developing fruit. Yet the fruit takes 6-9 months to mature. At the Chicago Botanic Garden, the spathe of their corpse flower wilted after about 3 months, exposing yet unripe fruit. Could the flower serve as protection for the developing carrion beetles? Is there any food supply for those youngsters when they hatch? Or is it just a dead end (pun intended)?
FYI: while other arums smell like corpses too (my personal favorite is the “pig-butt arum”), some species of Amorphophallus smell like bananas or carrots.
- Angioy AM et al. 2004. Function of the heater: the dead horse arum revisited. Proceedings of the Royal Society Biological Sciences. 271(3) S13-15.
- Barthlott W et al. 2009. A torch in the rain forest: thermogenesis of the Titan arum (Amorphophallus titanium). Plant Biology 11. 499-505.
Two robins (Turdus migratorius) hopped through the yard this week – spring is on its way. The sound of lawn mowers now drift through the air, confirming the avian prediction. Shockingly, these two very distinct signs of warming weather are actually related, according to a backyard research study conducted in 1979.
L.A. Eiserer conducted a series of scientific (well, somewhat) studies examining the impacts of lawn mowing on robin-hunting behaviors. Robins spend more time foraging when grass is short, especially just after it has been mowed.
So is it the mowing or the height of the grass that impacts robin behavior? Eiserer mowed his lawn to two different heights, 2.5 and 4.5 inches. (I wonder if his neighbors complained.) The robins spent 10x as much time in the shorter patch. Apparently, the birds eat different foods when exposed to different heights of grasses. In short grass, robins go for worms; in longer grass, they pluck small insects off the blades. The short-grassed hunting grounds may just be more efficient for finding a heartier meal.
But that doesn’t discount the act of mowing. Observations over the same time of day show the birds prefer hunting in a freshly mowed yard rather than the day after. No difference in grass height, but perhaps the act of mowing disturbs invertebrates, allowing for a more successful hunt.
Overall, I miss the days when a researcher could sit on a suburban porch and time how long a couple of robins spend looking for food. As I struggle to teach my students how to think like scientists, reading a study like this makes me long for the good old days.
Eiserer, L.A. 1980. Effects of Grass Length and Mowing on Foraging Behavior of the American Robin. The Auk. 97(3) 576-580.
I recently ran across this gorgeous beetle while hanging out with writer Scott Huler on his ambitious Lawson Trek. I didn’t know what species it was, but figured it would be pretty easy to ID when I got home (it was). As I began researching this insect, I quickly realized that the Patent-Leather Beetle (Odontotaenius disjunctus) should be nominated for a Best Insect Award.
1. Great Personality
This very large beetle with scary looking mouthparts won’t hurt you. It rarely flies and it’s a pretty slow walker… so no sudden movements and no buzzing around your head. I like that in an insect. And those horrifying chompers? They’re used to chew through logs, not people. Thank you, evolution.
2. Cool Appearance
Ooo, shiny! Plus, it’s a terrific insect for anatomy practice. First, no microscope needed. Second, that clear-cut case of head, thorax, abdomen? Not so fast. The abdomen-looking structure is actually a grooved set of hardened wings called elytra. And that thorax-looking structure? Well, it is PART of the thorax. The other section is underneath those elytra. Way to keep things interesting!
3. No Sexism
Both males and females contribute to rearing their young and keeping the home safe and tidy. This social structure is not common among beetles (see another post about equality-minded beetles).
4. Ecological Service
Patent-leather beetles don’t just raise their family in logs. They also eat and decompose the wood, recycling nutrients back to the forest floor.
5. Kiss Language
These beetles communicate with each other through a number of different calls. Many calls sound like the noise you make when blowing someone a kiss. Larval patent-leather beetles even have a modified third set of legs that create noises to communicate with parents (“Ma, I’m hungry!” “Watch me, Dad!”)
Want to learn more about the awesome Patent-leather beetles (and hear their kiss-calls)? Here’s a great resource from the University of Florida.
Dragonflies hover, swoop and twirl but never walk. They use their legs to trap their insect prey in a tiny six-barred prison before devouring them head-first. When guarding its territory along the water’s edge, this Blue Dasher (Pachydiplax longipennis) grasps a reed or blade of grass and waves his blue abdomen as a warning for other males. Females, in general, aren’t blue at all; they’re black with yellow lines running down their bodies While the name “dragonfly” may be confusing, other names – “snake doctor” or “devil’s darning needle”, for instance – are equally perplexing. No, dragonflies do not treat ailing snakes (or bring them back to life) and the insects don’t sew up any parts of you (although my Grandmother convinced me not to lie with the threat that dragonflies would sew my lips shut if I did). And in case you were wondering about that species name, it means “long wings”… not what you were thinking.