Category Archives: Insects

A fruit fly with swagger

It’s all about how you hold your wings. A seemingly unassuming fly, resting on gray denim, wings folded like calm hands:

Then twack the wings pop:

The peacock fly!

This dandy belongs to the picture-winged fly family (Ulidiidae), a clan for whom romance is expressed through ornamented dance. Wings quiver, feet stomp, heads tap. They seek rocks, twigs, and even human legs as ballrooms. Like other fruit flies, they feed by slurping sap and rotting fruit. Females lay eggs under punky bark or in rotting vegetation. The larvae squirm, a proto-dance of kinds, perhaps. This costumed strutter lingered for half an hour, playing the light through his wings, leaving only when his human Marley flooring moved on.

Dipteran-discovery, phone-camera, and choreography consultation credits: Katie Lehman.

Hair wax for sawflies

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A tuft of dog hair in the tree? No, the tangle is walking, hair a-tremble.

A closer look: legs, head, and puckered skin dotted with hair-nozzles.

These photos are old — from a few weeks ago — not not so old that the 1980s might serve as an excuse. Instead, these waxy locks are mouth-gumming defenses, reminiscent of my favorite aphid (oh the choice was hard), the boogie-woogie beech blight aphid. This is no aphid, though, nor a caterpillar, but a sawfly larva, the leaf-chewing life stage of Eriocampa juglandis, the “Butternut Woollyworm.”

Sawflies are wasps, not flies (Symphyta, within the Hymenoptera, for those playing ento-bingo). The “saw” in their name comes from the serrated ovipositors that the females use to lay their eggs inside plants. Eriocampa females oviposit in the midrib vein of the leaf, using the blades on the tips of their abdomens to pierce the plant and nestle sawflies-to-be in a bed of food. After an egg-laying female is done, the midrib looks like an evenly-stitched hem, punctured by two dozen or more regularly-spaced holes.

The young sawflies chew holes in leaves, often working in teams lined at leaf margins. Only when they reach their older years, after several molts, do the larvae grow their fabulous hair-dos.

Sand tracks

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“In every outthrust headland, in every curving beach, in every grain of sand there is a story of the earth.” Rachel Carson, writing in Holiday magazine, 1958.

From the curving beach of St Catherines Island, another blog post in the grapheme series (parts I, II, and III). Sand scribblings. For the full coastal Georgia effect, view in a steam room with the heat turned up to one hundred degrees. Click on any image for the slideshow:

Aphids: The Sequel

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I’ve been keeping my eye on the funky residents of the beech aphid colony, watching them groove the summer away. I found the colony back in late July when it was already quite large. It then grew a little, adding new clusters of young aphids, but gradually waned through September. This week, the last beech aphid departed, leaving just a few wisps of wax on the ground below. Over the weeks, the colony added more and more winged individuals. These are the individuals that disperse and mate; all others are asexual and sedentary.

Winged Beech Aphids, feeding among wingless forms (Grylloprociphilus imbricator)

Discarded strands of Beech Aphid wax on the mosses and lichens below the aphid colony

Discarded strands of Beech Aphid wax on the mosses and lichens below the colony

The day before I saw the last beech aphids, two newcomer species arrived on the twigs that had been the colony’s home. One was another aphid, a huge one. I thought at first that the beech aphids had somehow swelled and transformed, but another look confirmed that these new aphids are in fact a different species, the appropriately named giant bark aphid, (Longistigma caryae). For an aphid, they’re monstrously large, perhaps eight times the volume of a typical aphid. They also have long, sturdy hind legs, giving them a cricket-like appearance.

Giant bark aphid (youngsters on left, adult on right)

Like other aphids, this species feeds by sliding its needle-like mouthparts into plant phloem and eating the pressurized sugary sap that squirts through the needle into their guts. In their thirst for dilute nutrients like amino acids, they void the excess sugar, dropping sticky honeydew below. This is all too much for many gardeners and the ag extension agencies continue their long tradition of suggesting chemical sledgehammers to crush these nuisances. Malathion and Orthene? Really?

Hidden for now from the nozzleheads, these bark aphids took up residence in exactly the same spot as the beech aphids. I mean exactly: down to the centimeter. Are they exploiting the feeding holes or weakened bark left by their departed distant cousins? The coincidence is striking. The beech tree no doubt let out a sigh. One load of sugar-suckers gone — at last! — and another bunch of free-loaders show up. Bring on the freeze? Come hither migrant warblers?

The new residents brought their own private security team. The guards are paid with sugar and they take their work seriously. I’ve visited several times in the last week and the bark aphids always have three or four large honey-colored ants in attendance. The ants gather honeydew from the aphids, then stand and wait from the next drop. One ant filled her abdomen, then scuttled up the branch and found a skinny-looking sister. They stood head-to-head and the nectar was transferred, causing the second ants’ abdomen to swell into an amber globe. The first ant returned to her charges; the second scurried up the twigs into a blueberry bush, then I lost sight of her. I have no idea where the ants may be nesting. I’m keeping my eyes open.

I’d love to know more about the identify and natural history of the ants that are tending these aphids. Myrmecophiles, your insights would be received with gratitude. [Addendum: The ant is likely a carpenter ant, perhaps Camponotus americanus. . Thank you, Ann Fraser and AntWeb!]

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Nested sets

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Sandy Gilliam brought by this nest of a colony of bald-faced hornets (Dolichovespula maculata). The nest was attached to the wall of his barn.

bald faced hornet nest

Bald-faced hornets are well-known for the vigorous defense of their nests, a strategy that often follows the Bush Doctrine of pre-emptive strike. Unlike honeybees, the female wasps can sting repeatedly without harm to themselves.

But this nest had no angry occupants. It was abandoned last year when the winter set in. This is part of the normal life cycle of the species: a solitary female starts a nest in the spring, builds a large colony through the summer, then the whole colony dies except for young queens who overwinter alone.

A glance at the nest’s entrance (located at the bottom tip of nest) shows that this is a special nest. Straw and feathers protrude. We can peek into the opening and see a tunnel of dry stems.

bald faced hornet nest inside from bottom

The nest was built against a wall, so it has no backing. Now that the nest is down we can easily see inside: another nest! House sparrows had climbed into the old insect nest, added some bedding of their own, then set up shop to breed.

bald faced hornet nest inside

This was a stroke of avian genius. No chipmunk or squirrel would be stupid enough to try to raid this nest. (In the tropics, some birds take this further, protecting themselves from raiding monkeys by nesting next to active wasp nests.) The nest also comes with its own insulation system. The hornets build multiple layers of cellulose around the core of their nest, allowing them to stay warm through the night and thereby start work earlier than most insects (see The Thermal Warriors by Bernd Heinrich for more on the the various ways that insects manipulate their thermal environments). The incubating mother bird no doubt benefited from the extra warmth.

bald faced hornet nest wall

The nest retained its old comb, revealing the hornets’ kinship with bees. Here are the hexagonal arrays again, but this time built from chewed wood, not wax.

bald faced hornet nest comb

bald faced hornet nest comb close

Entomological enthusiasts should note that although we call these insects “hornets,” they are more accurately called “wasps” or “yellowjacket wasps.” True hornets belong to the genus Vespa and have bulkier heads and abdomens than the more slender “yellowjacket” species (Dolichovespula and Vespula).

I’ll close with my thanks to Sandy for bringing this remarkable nest-in-a-nest to my attention.

Parasitic ants, unwise language, and a little glimpse of Darwin

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Several weeks ago I came across a curious highway of ants. They were streaming across the leaf litter in a column about a foot wide. The column started under an oak tree, traversed the leaf litter and hiking trail, then ended abruptly about forty feet away in an otherwise unremarkable patch of fallen leaves. Ants traveling away from the tree were carrying white, ant-sized objects in their jaws. Ants moving in the opposite direction were empty-mouthed. At the destination, a few smaller ants milled about, seemingly at ease among the larger ants that I was watching.

I suspected at the time that I was witnessing a raid by a so-called slave-making ant species. My skills as an ant taxonomist are limited and I turned to my colleagues for help. Thanks to James Trager and Ann Fraser, I’ve confirmed my suspicion and been able to tentatively identify the species in question as Formica subintegra and Formica subsericea (an aside: Ant Blog is a great place to seek answers about ants). The first species, the larger one, was attacking the nest of the other and carrying away eggs and larvae. These captured youngsters will be raised in the “den of thieves” and, when they emerge as adults, the newly pupated ants will have no idea that they do not belong. Because ants take their cues from the chemical milieu in which they grow up, the stolen ants consider themselves full members of the alien colony. This trickery buys the captors a work force to maintain the nest and rear more young. In some ant species, the captors are so dependent on the captured workers that they cannot survive without them, having lost the ability to feed themselves and take care of the brood.

In the biological literature this arrangement has, for many years, been called “slave-making.” This makes me deeply uncomfortable. Using a term — slavery — from a human institution that all (or nearly all) modern human societies have agreed is morally unacceptable seems unwise. Further, the “ant slavery” term implies a biological equivalence that does not exist. There is not a single biological parallel between the details of the situations in humans and ants (ants raid other species, ant societies and nervous systems differ radically from ours, etc). By using a term derived from human society, a term that comes with considerable moral heft, we blind ourselves to the otherness of the ants. So in addition to the moral argument (which is strong enough on its own, I think), there are scientific reasons for not using the term: our preconceptions may cause us to fail to understand ant biology.

In other areas of biology, we’ve thankfully tidied up our terminology a bit. Textbooks on animal behavior were formerly strewn with terms like divorce, rape, and prostitution. These days, textbooks generally leave these loaded terms at the door, although more popular media outlets and some scientists continue the unfortunate practice. For example: Wikipedia (of course), BBC, and The Independent (note how the coverage slips so easily into discussion of what is natural for humans; Hume shudders, as explained (of course) on Wikipedia). My point is not that conflict, coercion and suffering do not occur in nature (of course they do), but that the use of human categories to describe animal behaviors can lead us into trouble. This is especially true when those categories carry with them a strong emotional, intellectual or moral charge.

Back to the ants. I was particularly excited to see this process unfold because it has a place in the history of biological ideas. Darwin was fascinated by these ants and used them in Chapter Eight of On The Origin of Species as an example of how natural selection could mold behavior (or “instinct” as he called it). He writes:

We shall, perhaps, best understand how instincts in a state of nature have become modified by selection by considering a few cases. I will select only three, namely, the instinct which leads the cuckoo to lay her eggs in other birds’ nests; the slave-making instinct of certain ants; and the cell-making power of the hive-bee: these two latter instincts have generally and justly been ranked by naturalists as the most wonderful of all known instincts.

Darwin dug up and manipulated a number of nests in England, experimenting with the ants to better understand the nature of the “slaves” and “masters” as he termed them (Darwin was not shy here or elsewhere in his writing about linguistic cross-over from human behavior). He concludes that:

…natural selection might increase and modify the [parasitic] instinct—always supposing each modification to be of use to the species—until an ant was formed as abjectly dependent on its slaves as is the Formica rufescens.

The complete account is available in the many online copies of The Origin (or in the treasured copy of this volume on your bookshelf).

In the years since Darwin, hundreds of studies have been conducted on the socially parasitic ants, many of which are summarized in a short review by Buschinger. One recent study of particular note is the discovery of retaliation by a genus of ant that is frequently attacked by parasites. The host genus is Temnothorax — tiny ants that nest inside acorns (!) and hollow twigs — and the parasite is Protomognathus americanus. Unlike the larva-robbers that I observed, Protomognathus parasitic ants invade and take over the nest of the host. Temnothorax adults are killed and their young are co-opted to work for the parasite. It appears that these attacks are so common that natural selection has produced a counter-measure: genes in some of the host workers cause them to attack the parasite, killing the developing Protomognathus pupae.

The authors regrettably use the terms “slave rebellion” and “revolt against their oppressors” to describe the behaviors that they describe. Surely a human rebellion against slavery is biologically and morally different than a gene variant causing an ant to use chemical cues to bite a pupa? My grousing about language aside, this is a remarkable study. Darwin would have loved to add this co-evolutionary tale to his chapter on the evolution of animal behavior.

From now on, I’ll be examining acorns more closely.

Carpentry

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I’ve been using some salvaged wood to make repairs to the goat barn. One of the pieces seemed unusually light. I flipped it over and found a perfectly round hole on one side: the entranceway of a female Eastern carpenter bee, Xylocopa virginica.

The bee that left this hole used her mandibles to gnaw into the wood, then she slowly tunneled through the timber. I’ve seen these bees at work on the rafters of several of the small barns that we’ve built for animals and hay. On a quiet day in early summer you can hear the crunching of chitin on wood as the bees make their slow progress. Below the holes, small piles of sawdust accumulate.

I’ve seen many entrance holes, but never had the opportunity to see the extent of the tunnels inside. So I made a series of longitudinal cuts in my wood scrap, a 4×4 dissection of sorts. Inside, I found the tunnels extended about a foot away from the hole. One or two tunnels branched. This is an impressive hidden network, like a subway with just one exit. No wonder the piece of wood was so light.

The bees make these tunnels for their young. The female makes a ball of pollen and nectar, then lays an egg. All this is sealed into the tunnel with a slug of compressed sawdust. Once the passage is sealed, the mother leaves her offspring to their fates. These futures sometimes involve woodpecker beaks. The drilling of these hungry birds will finish what the bees started. The two species, bee and bird, are an anti-carpentry team. But I also think of these animals as supreme carpenters: they’ve been making homes from wood for millions of years and they spend their lives happily sprinkled with the sawdust of their labor. So they are both über- and anti-carpenters.

Away from wood, the bees do good work as pollinators. They are eager visitors to many species of flowering plant. Some farmers even erect pieces of wood to attract them into their orchards. I’m OK with a few at our place, but a year ago we had an invasion of battalions of barn-destroyers. So I relived my glory days of college squash-playing, dispatching them with a killer backhand from a dustpan. I felt bad, but not as bad as I would have had the barn needed rebuilding. These days we just have a few carpenter bees buzzing around and I leave them alone.

Three-way partnership = bad news for a two-by-four

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This old piece of pine lumber (the stub end of a two-by-four) has been devoured by termites. The rest of our garage has been spared their attentions, so far.

A weighty block has turned to crumbly paper. The insects responsible for this impressive work were scurrying nervously in the too-bright light of day, each one looking like a fat grain of rice from a milk pudding. Add sugar and I’m ready to become an myrmecophage (yes, anteaters love termites).

Termites are like cows, they graze on plant material that is completely indigestible to them. Only by harboring an internal band of helpers can termites (and cows) free the nutrients and energy locked in woody tissues. The termites’ helpers are in the hind part of the gut. Here single-celled protists (relatives of “amoebae”) engulf small wood particles and digest them. But these protists are cows too…they have within their cells a peculiar group of bacteria, the critters that do the actual work of making wood-destroying enzymes. So helpers live within helpers.

The fact that only a few obscure groups of bacteria can digest cellulose (the main component of “wood”) explains a lot about our world. If more creatures could digest wood, then trees likely could not exist (their trunks would be gobbled up in short order), wooden structures would last about as long as gingerbread houses (which are, I’m told, digestible, explaining perhaps their limited popularity outside of confectioners), and our great stockpiles of coal (old compressed wood) would not exist. No forests, no houses, and no industrial revolutions (at least not coaly ones…and what other kind has there been?).

Cute larvae. Adults are a different story.

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Looking down on this fast-flowing stream in Shakerag Hollow we see wavy lines on the submerged rocks. Moss? Algae? No, ...

...these are clusters of blackfly larvae (Fanily Simuliidae). Each larva is attached to the rock with claspers on its rear end; silky threads provide additional anchorage. They prefer the fastest flowing parts of the stream, so these attachments are strong.

With a flash photo, we can see the larvae leaning with the current. They thrive in the oxygenated water of unpolluted streams.

Two fan-like feeding appendages crown each animal. The fans are used to sieve bacteria, algae, and small pieces of plant material from the flowing water. In good conditions, every few seconds the fans sweep food into the animal's mouth.

After a few weeks, the larvae pupate underwater (still attached to the rock in flowing water), then emerge as the infamous flying adults. Males feed on nectar, but females want blood. Unlike the swarms that emerge in northern states, blackflies are seldom numerous here.

Sing on, grave crickets

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This morning, before the rainy front moved in, I heard a remarkable thing — crickets singing softly from the long grass under a powerline (field crickets, genus Gryllus, I think). We’ve had several hard freezes, two modest snowstorms, and the days are about as short as they get. Yet, they sing on.

Our culture has a long tradition of moralizing about these singing orthopterans, starting but not ending with Aesop.

Wastrel Fools! Squandering summer while the provident ants buckle under and work.

Or, Happy Fools! Sing while you can, for tomorrow we die.

As the title of this post suggests, the crickets seem to me to offer an alterantive to Dylan Thomas’ rage — why not sing, sing as you go gentle into that good night? A song is more defiant than rage.

So far, so good. These little tales are hardly masterful works of nuanced allegory, but they make their point. What the literary encrustations don’t do is honor the actual insects. We see ourselves reflected in their lives, but the mirror itself is invisible.

Here’s a brief take from a biologist’s perspective: evolution has molded each species to the particularities of the ecological situation. There are many ways of being a successful insect. Diversity wins the day.

Crickets overwinter as eggs, a thrifty strategy that requires no food stores. In the spring and summer, the eggs will hatch and several generations of crickets will follow before the winter comes again. Ants overwinter as colonies of sterile workers tending their fecund queen (she truly is “the 1%”). Because the colony has so many workers, it needs food stores to make it through the winter. Both strategies have worked for tens of millions of years.

Ironically, ants also eat cricket eggs to make it through the winter. In fact, hungry ants are a major source of mortality for cricket eggs. So, it seems that we need each other after all.

Hello? Aesop, are you there?