Category Archives: Caterpillars

Tussock moth caterpillar

2015-06-29 tussock moth caterpillar 001revA White-marked Tussock Moth (Orgyia leucostigma), one of the more festive of our caterpillars. They have a catholic diet, eating both evergreens and deciduous trees, a feat made possible by their robust gut chemistry.

The caterpillars not only use their hairs for defense (and advertisement of that defense), but use them to sense attacks and respond appropriately. The caterpillars drop to the ground if their hairs are jostled by a fast-moving object. They trundle away when the agitation is calmer. Thus they avoid common predators: Polistes wasps that pounce in an aerial attack, Sinea assassin bugs that launch ambushes from the leaf, and Podisus stink bugs that amble up and probe with mouthparts. Dropping is a good defense against the former two. Walking away is sufficient for the latter.

2015-06-29 tussock moth caterpillar 008The adults are also interesting, but not nearly so bright. The female is wingless and emits a pheromone that the well-antennaed male follows upwind.

“Caterpillars” in The Forest Unseen has more on this species, including some reflections on how struggles with predators change the pattern of light in the forest. Well-haired caterpillars can afford to reveal their locations by shot-gunning leaves with holes. Undefended species are more tidy eaters. Spineless? Tidy your plate.



Caterpillars taking their tithe of the carrot tops

Nightly frosts brush the garden, but botanical energy continues to surge. Carrots, lettuces, and chard are all thriving in the cool sunshine. Black swallowtail butterflies have tapped this energy, laying eggs on the carrot leaves. The caterpillars fall into an inert stupor during the cold nights, but turn into animated single-minded leaf-munchers when the sun touches their skin. They are all in their last stage of molt. The next step will be transformation into overwintering pupae.

2014-10-22 swallowtail caterpillar 0102014-10-22 swallowtail caterpillar 0042014-10-22 swallowtail caterpillar 005For reasons unknown to me, Linnaeus named many swallowtails for prominent figures in Homeric/Greek poems. The black swallowtail is named (polyxenes) for Polyxena, the daughter of Priam, King of Troy. She does not appear in the Iliad but other accounts tell that her death marked the end of the Trojan War. The connection between these tales and North American butterflies seems tenuous, at best. But Linnaeus invented the rules of nomenclature, so he could do as he pleased.

Our caterpillars need not fear Achilles and, with luck, the birds will not find them.

Spicebush swallowtail caterpillar

My colleague David Johnson’s Field Investigations in Biology class found this caterpillar on one of their forays into the woods. The animal was discovered hitching a ride on a student’s boot and was brought back to campus for the admiring crowds. I kidnapped it (the caterpillar, not the boot) for a photo shoot.

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This caterpillar does a fabulous impression of an outrageously colorful snake. Note the light “reflection spots” within each “eye.” When distressed, the caterpillar will apparently inflate its head and rear up. I poked it a little, but could get no response. I did not feel like tearing at its skin like a real predator (my inner blue jay would not come to the surface), so the snake-charming will have to wait for another day.

Spicebush swallowtail caterpillars spend their first few instars (“life stages”) looking like bird droppings. This allows them to loiter in plain view and they generally sit on the upper surface of leaves. Their last instar is the snake-mimic. At this stage they roll leaves into loose cigars and hide inside the bore of the roll. Their snaky heads face outward.

The caterpillar will shortly turn into a crusty brown pupa from which the adult butterfly will emerge in the spring. Sewanee has plenty of the species’ two host-plants — spicebush and sassafras — so this species is quite abundant, but the spectacular caterpillar is surprisingly hard to find.

Crowned Slug Moth, Isa textula

I came across this tiny (1.5 cm long) but handsome caterpillar on my walk to Piney Point this morning. It was lying immobile in the trail, under a white oak. Wagner’s Caterpillars of Eastern North America (what a great book!) notes that these caterpillars “may be active very late in the season, sometimes dropping down with autumn rains and winds.” After photographing the animal, I placed it on an adjacent oak sapling.

Murphy, Lill and Epstein’s study in the Journal of the Lepidopterists’ Society has some interesting background information on these caterpillars. They belong to the Limacodidae family, the so-called “slug caterpillar moths,” a group named for their strange offspring. All the species in the family have caterpillars that look like gummy worms going through a punk adolescence. Studs and spiky hair adorn colorful pudgy bodies. They can deliver quite a sting, as I noted a few weeks ago in my post about the saddleback, a different species in this family.

Murphy et al. confirm Wagner’s statement about the lateness of the species. This species is one of the season’s last active caterpillars, and are “frequently found feeding on leaves in the midst of turning color in late October, right up until leaf drop.”

Once they have finished growing, the caterpillars find a safe nook, then make a cocoon in which they enter a state of suspended animation (known as “diapause” in the zoological world). In the spring they make a pupa within the winter cocoon, then transform into an adult moth.

Saddleback caterpillar, Acharia stimulea

The pain receptors on Marianne Tyndall’s arm found this impressively spiny caterpillar on some garden vegetation yesterday. The caterpillar is about two inches long. Its sting causes pain that feels like a combination of burning skin and tearing muscle. Pretty impressive. The pain is bad enough to cause some people to call a poison center, as reported here. Note that the paper in this link uses the old genus name, Sibine. The paper also relates events in Louisiana where people evidently have different attitudes to caterpillar attacks — in Sewanee, we suck up the pain, then carefully gather the caterpillar to bring it to fellow naturalists.

The stinging hairs deter predatory wasps and assassin bugs. Wasps learn to recognize the caterpillars and after a few inspections, leave them well alone.

The colorful caterpillar turns into a fuzzy brown moth.

Goslings and caterpillar

Continuing with the theme of cute animals, I was in Chattanooga today and took time out for a bike ride along the Riverwalk. Young animals from two very different parts of the tree of life caught my attention.

This mixed brood of Canada goose goslings was making its way upstream along the Tennessee River. There are at least two families, possibly three, in this “crèche.” Mixing families like this is common in waterfowl, although less so among Canada geese. There is safety in numbers, so these goslings benefit from each other’s presence.

This pipevine swallowtail caterpillar was crossing the concrete path. Although it looks fearsome, it is harmless to handle. But any would-be predator foolish enough to try to eat the caterpillar will soon regret its decision. These caterpillars feed on poisonous pipevine plants and sequester the toxins in their bodies. The toxins then get passed to the adult butterfly. The adult tastes so nasty that half a dozen other species of butterfly mimic the butterfly’s blue and black colors, gaining protection through deception. Predators generally leave these mimics alone for fear of biting into a pipevine swallowtail. The photo below is from last summer — note the remarkable iridescent blue. Although I frequently encounter the adults I have never before seen the caterpillar. So a close encounter with this bristly rubbery beast made my day. I put it back in the vegetation, away from the walkway.

Inching into the future

I’m visiting the University of Richmond where, just like Sewanee, spring is in full force and many weeks early. In addition to great people and beautiful buildings, the campus is populated by millions of inchworm caterpillars. Just walking between buildings results in the acquisition of half a dozen hitch-hikers, each one hanging by a silk thread from above, presumably drfiting down to new feeding areas or places to pupate. These caterpillars belong to the Geometrid moths, a family of brown moths named for the looping walking habit of the caterpillars — they appear to “measure, metron, the Earth,Geo,” as they walk along.

These seemingly insignificant creatures are one of the hinges on which our changing world swings.

The caterpillars come out when the oaks and other trees first unfurl their leaves. The young leaves have not yet had time to accumulate toxins to deter the inchworms, so the little caterpillars feast quickly, then their numbers dwindle.

Migrant birds time their arrival to catch the burst of caterpillars (food!). But, lately, the caterpillars are emerging so early that by the time the migrant birds arrive, the party is over. In Europe, this mistiming is so severe that it has caused significant population declines in some birds.

How or whether these dissonant changes in tempo will resolve is unclear.