Category Archives: Beetles

Woodland family values: carrion beetles

Matt Schrader, my colleague in the Biology Department, keeps colonies of burying beetles in his lab. He studies the evolution of their behavior, especially the care that the parent beetles bestow on their young.

Nicrophorus beetles find small carrion — mice and birds — then bustle over the cadaver, preparing it for the young. Many species shave the corpse, some roll it into a ball, and a few chew then regurgitate the meat to their young. The growing beetles therefore live under the protection of their parents, an unusual arrangement among beetles, most of whom pass childhood without knowing solicitous parental care.

Nicrophorus tomentosus (the gold-necked carrion beetle) larvae on a mouse cadaver.

Other species, especially bacteria and fungi, also want to feast on the dead meat, so the parents paint the corpse with an antibacterial exudate. When threatened, the ooze also serves as a stinking defense mechanism.

Stay away…and have a free dose of antibiotics.

Like other carrion beetles, Nicrophorus tomentosus have orange and black stripes across their wings. This is probably a warning signal to potential predators, like the bands on a poisonous caterpillar. Keep off, we taste bad. When the beetles take to the air, they reveal another signal: they sound and look like bumblebees in flight. Underwings are bright yellow and thrum just like a bee. Another layer of defense, perhaps?

Stripes.

Underwing yellow. The flight of the bumblebee, interpreted by a carrion beetle.

Another moniker for these beetles is the “Sexton Beetle”: These animals are the caretakers of the forests’ graves, with more flashy garb than their human counterparts.

Who left all these twigs in the woods? 2015 is the year of girdled hickory.

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Coleopteran work crews are trimming the forest canopy. Their leavings are scattered all over the leaf litter, in a profusion that I’ve never seen. Next spring’s hickory trees will therefore cast less shade and we’ll see the beetles’ legacy in a patchwork of sunlight. Canopy openings will admit more sky into the understory, fattening citrine spring-light with blues and reds.

The arborists are Oncideres cingulata, hickory twig-girdlers. The beetles’ bodies are stubby, just a half inch long, and their colors match the chestnut-ash blotching of hickory twigs. In late summer and autumn adults feed on the delicate bark of hickory twigs, chewing the soft phloem tissues through which the tree transports its sugars. These twigs also serve as mating sites, all-you-can-eat-buffets doubling as dating clubs.

Twigs then serve as nurseries. Females lay eggs under the bark, sometimes peppering a single twig with a dozen or more piercings. Then, the mothers go to work with their sharp mandibles, gnawing a ring around the twig. They start at the bark then, lathe-like, they rotate until the twig breaks away, leaving a few torn wood strands at the center of a clean cut. It is these shed twigs that are strewn everywhere. Lately I’ve seen one hundred or more on a short woodland walk.

Eggs hatch in late autumn and the larvae set to work within the fallen twigs, using symbiotic fungi to turn inedible wood into a paste of yum. In spring, when the weather has warmed, the larvae expand their activities, riddling the wood with tunnels. Beetle runnelling? They stay under the bark, emerging only to expel sawdust. In summer, the full-grown larvae gnaw small chambers into the twig, then curl up and pupate. The adults that emerges fly to the treetops to start on fresh twigs. Why the majority of this species’ life cycle is spent on the ground, inside fallen twigs, rather than on unfelled twigs, is a mystery. Perhaps the girdling shuts down the flow of defensive chemicals from the trees’ branches. The ground is warmer, too, giving the larvae more work days. Or woodpeckers may be less likely to drill the youngsters from fallen twigs than from standing branches. Whatever the reason, the stem litter underfoot evinces the beetles’ success.

I’ll put a girdle around the twig / In forty minutes ~ Oncideres puck

Bark scars: eggs are nestled below, inside the wood.

White pine wood for breakfast

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You can hear them from twelve feet away. Rhythmic grating sounds from within a dead white pine tree in our neighbor’s yard. Sarah heard them first on her early morning walk. We returned later in the day, but the munchers had fallen silent. It seems that their appetite is keenest at dawn.

Here are the sounds, with a labeled spectrogram of the same sound. I suspect that the crunching sounds are coming from large Cerambycid larvae (long-horned beetles). The hairy woodpecker that was diligently extracting them from under the bark would know for sure. Beetle larvae that live under bark can thrive on seemingly indigestible wood using a combination of detoxifying enzymes produced by their own guts and through use of cellulose-digesting enzymes that the insects derive from the fungi that live inside the wood. This is a bit like digesting moldy cornflakes by harnessing the power of the mold. A clever strategy, but one that I’ll leave to the beetles.

Spectrogram (time moves left to right; frequency (pitch) is on the vertical axis):

Invasion of the ladybugs. UN treaties violated.

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An airborne invasion of ladybugs has turned Sewanee into a pointillist’s drunken joke. Our house has several thousand of them jostling on the southern wall, with a few hundred making their way through hidden cracks to the interior. As I type, they bombard the keyboard. Walking outside, I get them in my hair, down my shirt, into pockets.

A plague of coleoptera? That seems to be the general opinion in town, with calls for chemical weaponry not far behind. More on that later.

Who are these creatures? They are Harlequin ladybird beetles (Harmonia axyridis), also known as Asian ladybugs or multicolored lady beetles. They’re looking for shelter over the winter. Any crack will do. The more the merrier: they call to each other with chemical attractants, possibly because there is safety in numbers.

These insects were first brought from east Asia to America in an attempt to enlist them in our never-ending fight against aphids. So the legions of ladybugs banging against our walls are a testament to the foresight of the USDA and a witness to the prodigious numbers of aphids that, despite their new Asian foes, crowd like feedlot cows on twigs and flower stems.

If swarms of colored beetles were a rare occurrence, the military-industrial-wedding-complex would be charging big bucks for uplifting releases of these merry air-dancers. No such luck: these insects have crossed the cultural threshold that divides purty from plague. How to deal with them? Some companies make lures and traps, decoying the beetles with a mimic of their aggregation pheromones. I have no experience with these devices, but I suspect that they are only partly successful. Like a liquor store on the edge of a college town, you’ll grab some of the swarm, but many others will BYO and head straight to the party. Vacuums work well on smaller swarms and a mesh or nylon stocking placed inside the suction tube (trap it between tube sections) will keep the doomed beetles out of your bag. Or just wait and they’ll disperse or die on their own. Eventually.

But this is not just a story about Homo vacuumus. These beetles may quite literally have a silver lining. Their ecological success is partly due to their invulnerability to disease, a super-power conferred by their “hemolymph” (insect blood). The potency of this vital essence is easily confirmed: poke a beetle and see the defensive yellow ooze of blood emerge from chinks in their legs, staining your hand and releasing a powerful odor. Studies of the antimicrobial properties of the blood show that it contains a chemical, harmonine, that inhibits both TB and malaria. Knowing this, I pick the ladybugs out of my hair with new found respect and even a sense of hope that medical wonders may yet emerge from the entomological onslaught.

The weaponry story does not end here, though. These insects not only carry chemical defenses in their blood, they may also attack competitors with biological weapons. A microbe that lives peacefully on the harlequin ladybug appears to be lethal to native ladybugs. When these natives prey on the eggs of the harlequin ladybug, the microbe attacks and death follows.

In sum: we’re under attack from insects that are in violation of multiple international arms agreements. Enjoy the spectacle.

Dead wood, ashes.

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One of Shakerag Hollow’s giant trees has fallen. An ash that until last week held its arms in the highest reaches of the canopy now sprawls across the forest floor, its body utterly torn. I’ll go back soon and “measure” things (how tall? what weight of wood came slamming down?), but for now: just awe.

I did not see the fall, but came by soon after. The trunk was … indescribable. Some grand words are needed, for barely imaginable violence had been at work. Rent asunder!? The whole wide trunk was twisted and split open, lengthways, in several long gashes. Other trees, themselves no mere saplings, were smashed into the ground. Large boulders were shifted as roots reared and cracked. The air was infused with the odor of fresh-split wood. An overtone of bitterness, like cut oak, but mostly a sweet smell, almost honeyed.

I found the tree in the morning and returned in later in the day for another look. As I stepped closer in the warm afternoon, I hesitated then held back. There were wasp-like creatures, big ones, swarming over one of the thick exposed roots. These insects were scurrying, flickering their wings, crawling over each other. A frenzy.

Black with bold yellow stripes. Buzzing as they flew. Had the tree fall unearthed a buried wasp nest?

But something was not quite right about these wasps. I moved forward slowly and saw their fat hind legs, too beefy for a wasp. Crickets? No. Then the wing cases, striped in black and yellow: beetles! Wasp-mimicking beetles of some kind. I moved to the side of the tree and saw hundreds of them, racing up and down the bark. They were on no other trees nearby. Half of the beetles were copulating; the other half seemed intent on colliding with the mating pairs. Even though I now knew that they were harmless, their waspy nature made me cautious. Even their short curved antennae were creepily hymenopteran in style (oh yes, those hymenoptera have style).

Who were they? To identify them, I spent some time in the online funhouse known as the Photographic Atlas of the Cerambycidae of the World. This is an amazing site devoted to a single family of beetles, the so-called longhorns (although many of them do not have long antennae). The family contains twenty thousand species, an impressive number when we remember that there are fewer than six thousand mammal species. Some of these cerambid beetles run afoul of humans when they bore into trees and wood that we’d rather they stayed out of. A few of them are “invasive exotics,” killing off native plants. But the beetles in Shakerag were natives: Banded Ash Borers (Neoclytus caprea (Say) 1824). They have an interesting life history, finding recently downed ash and oak trees, then laying their eggs in the bark. The larvae then chew on the wood below the bark, emerging next spring to start the hunt for a newly downed tree.

So I was not the only creature in Shakerag following my nose to the smell of ripped up wood. How many huge ash trees have fallen lately? Not many. Every banded borer within miles must have been at this party. Those flickering antennae are surely tuned to the chemical particularities of newly opened ash wood.

The beetles were one of the very first arrivals in the tree’s new existence. When a large tree falls, its ecological life still stretches out into the future. Perhaps half of the animals (and many more of the fungi) that the tree will nurture during its existence arrive after the tree has fallen. The ecological vitality of a forest can be judged by how may large trees are lying around, feeding beetles, hiding salamanders, growing fungi.

To paraphrase Mr. Faulkner, “Dead wood is never past, it’s not even dead.”

Eastern Hercules beetle — Dynastes tityus

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I found this impressive beetle lying dead alongside the trail in Abbo’s Alley. The two large horns identify it as a male. The somewhat fearsome appearance belies the animal’s nature. Hercules beetles are harmless creatures, feeding on rotting wood as larvae (fat white grubs, usually found in dead wood or tree holes) and nibbling on leaves or plant sap as adults. The horns are used as wrestling aides when males tussle during the mating season.