Camo caterpillars and the birds that eat them

 

A Red-eyed Vireo (Vireo olivaceus) in a characteristic hunting posture. The bird is searching for its major prey, the caterpillars of moths. It has its head cocked upwards, searching the lower surfaces of the leaves above, as that's where many caterpillars hide during the day. Lepidopteran larvae - and those are OVERWHELMING moth caterpillars (not butterfly caterpillars) - are the vireo's major food source. During a long summer day, the roughly 130 million Red-eyed Vireos breeding in the U.S. and Canada consume something on the order of 4 billion caterpillars. Hard to believe but based on what is known of their foraging rate and dominant prey items, that's how the numbers shake out.

A Prothonotary Warbler (Protonotaria citrea) with a freshly harvested caterpillar (unsure of species). Almost all of the 38 warbler species that breed in eastern North America eats scads of caterpillars, and so do most groups of songbirds. So do some nonpasserine species, most notably the cuckoos. Many of these birds are migrants that winter in more southerly haunts, often in Central or South America, and migrate northward during the breeding season to exploit the eastern deciduous forest region's vast bounty of caterpillars. As this is crop is only seasonally available, many of these bird species must travel back to warmer climes for the winter - where they undoubtedly also consume great numbers of caterpillars.

If you are a caterpillar, you don't want to be grabbed and eaten by a bird. Evolutionary warfare between caterpillars and birds is probably the main driver of some incredible caterpillar camouflage. If you are a plant-eating caterpillar and can become ever more like the appearance of the plants that you feed on, the odds of surviving surely goes up. Birds are endowed with incredibly keen eyesight and are quite adept at spotting larvae. They still find plenty, and between the avifauna and all of the other predators that take out caterpillars, the survivorship can be as low as 1% in some moth species. So, every advantage that a caterpillar can get to thwart predators becomes very important.

Following are some photos, most from recent forays, that showcase examples of incredible botanical (and gall) mimicry by members of the larval crowd.

Late summer and fall foliage become dappled with color as the chlorophyll fades and leaf tissue begins dying. This plump Blinded Sphinx Moth (Paonias excaecata) caterpillar displays reddish patches that mimic autumnal foliage, in this case Hop-hornbeam (Ostrya virginiana).

This is a sister species of the caterpillar above, the Small-eyed Sphinx (Paonias myops), which also sports rusty dots that resemble necrotic leaf tissue.

This is a personal favorite of the leaf-edge mimicry crowd, a Double-toothed Prominent (Nerice bidentata). It is a specialist of elms, and in our part of the world that's almost entirely American Elm (Ulmus americana) and Red Elm (U. rubra). We find them on both of this species with roughly equal frequency. The back of the caterpillar is scalloped, much like the rough marginal serrations of elm leaves. As it eats into the leaf, the caterpillar becomes the leaf.

This is another elm specialist (mostly at least, it is also said to eat basswood), and its moniker is apropos: Elm Sphinx (Ceratomia amyntor). When at rest on the underside of an elm leaf, as above, the caterpillar typically aligns itself with the prominent midrib of the leaf. The caterpillar also has a raised stripe down the center of its back. The cat's lateral lines are arrayed at acute angles to its pseudo midrib and mirror the angled venation of the elm leaf. In effect, the caterpillar becomes a continuation of the leaf's veins.

Few can match the Checker-fringed Prominent (Schizura ipomoeae) caterpillar's ability to become one with the leaf. This one (the head is to the bottom) is consuming an old dogwood leaf and as is typical, the caterpillar is eating inwards from the leaf's edge. In essence, it becomes the leaf and spotting one of these can be quite difficult even when it is right in front of you. Sharp-eyed botanists might note the cat's scientific epithet: ipomoeae. That references a genus of morning-glories and is probably a misnomer, as this caterpillar probably never eats those plants.

Few do twig mimicry better than the caterpillar of the Dot-lined White Moth (Artace cribaria). They are virtually impossible to see as they lay plastered to twigs, despite being a hefty cat.

Another brilliant example of twig mimicry is the Yellow Slant-line Moth caterpillar (Tetracis crocallata). This is one of the inchworms in the massive Geometrid family, and many inchworms are twig mimics. When not feeding, they attach themselves to a twig of similar diameter and color, and often adopt an acute outward angle. In the case of this species, the head is jagged and pale yellow, exactly as a broken-off branch would appear.

A Redbud (Cercis canadensis) leaf, with what appears to be a raised reddish gall. Such leaf galls are commonplace, and can be formed by many organisms: bacteria, fungi, aphids, midges, wasps and others. Birds don't eat them, insofar as I know.

But wait! Closer examination shows that our leaf "gall" is not a gall at all. It is a Red-crossed Button Slug caterpillar (Tortricidia pallida). Slug moth caterpillars are fascinating as a rule, as are the "cute" little moths that they become. As caterpillars, many species appear to mimic the look of leaf anomalies such as galls, and they can be hard to spot.

This is just a tiny tip of the lepidopteran iceberg when it comes to caterpillar mimicry, much of which is presumably driven by sharp-eyed birds that attempt to feed ravenously on the caterpillar crowd.

Epic caterpillaring results in many cool finds

 

Cherry Dagger moth caterpillar (Acronicta hasta)

Shauna and I spent last weekend at the fabulous Highlands Nature Sanctuary in Highland County, Ohio, which is owned by the Arc of Appalachia. A bunch of us were there for our 12th annual "caterpillar safari", which is just a bunch of larvally-minded friends of ecology gathering to seek out the always fascinating caterpillars of moths (mostly) and butterflies (far fewer in numbers and diversity). Now is peak season for caterpillar abundance and diversity, and we prowled into the wee hours on Friday and Saturday nights, exploring interesting habitats. Most caterpillars are active nocturnally, so hunters of them must adjust their search hours accordingly.

Dozens of species of caterpillars were found and photographed, including this Cherry Dagger (Acronicta hasta). We brought lots of livestock back to the Arc's forest museum - our base camp - and from 10 am - 2 pm the public is invited in. Dozens of people got to see crazy larvae that they likely never knew existed. One should not underestimate the value of moth larvae (which the overwhelming number of caterpillars are). They are the primary organisms that convert plant matter into a digestible form of protein for birds and myriad other animals and underpin food webs.

Gray Hairstreak caterpillar (Strymon melinus)

We certainly do not ignore the occasional butterfly caterpillar that turns up, and this was a particularly interesting one. It is the caterpillar of the Gray Hairstreak (Strymon melinus), which specializes on feeding upon species in the Pea Family (Fabaceae). These cats resemble Mike & Ike candies and are tiny and easily overlooked.

This one is feeding on a tick-trefoil in the genus Desmodium. Many hikers know this group of plants by their triangular loments (fruit) that are thickly beset with stout hooked hairs. They evolved for mammalian dispersal, and that includes the clothing worn by humans. Those loments can be tough to get off and will even survive trips through the washing machine.

Here's what that Gray Hairstreak caterpillar in the previous image will (hopefully) morph into - one of our showiest butterflies. I say "hopefully" because the survivorship of caterpillars is astonishingly low. Just about everything wants to eat them and for some species of moths, at least, probably only one percent or so of caterpillars make it through the complete life cycle and to the mature reproductive stage. The rest become part of a great food chain. To compensate for such high mortality, butterflies and moths lay enormous numbers of eggs; a carpet-bombing strategy if you will.

Finally, a cool little-known thing about Gray Hairstreak butterflies. John Howard showed this to me a while back. Hairstreaks habitually rub their hind wings together, and the "tails" resemble antennae. Perhaps this pseudo face with its twitching antennae fools birds and other would-be predators who then lunge at the wrong end of the butterfly. While the hairstreak may lose parts of its hind wings, it might still escape to live another day and find a mate and reproduce.

Anyway, as John pointed out, if you can get directly behind the hairstreak and under it (that can take some effort), the lateral fringes form the illusion of orange eyes capped with long antennae, and even a frowning mouth below. Whether all of that evolved to spook visual predators I do not know, but whatever the case it certainly looks cool. And once a butterfly photographer knows this, they may find themselves spending much time attempting to get into position to get this shot.

Blanchard's Cricket Frog

 

As always, click the image to enlarge

Blanchard's Cricket Frog (Acris blanchardi) can be tough to see. This is Ohio's smallest frog, measuring a wee 0.6 inches in length and weighing but a gram. They are also cryptically patterned and blend well with their surroundings. While exploring an Adams County (Ohio) prairie last Saturday, August 31, we saw dozens of them around a small pond. The section of muddy shoreline that we explored had many dozens of frogs. The elfins make one work for a good photo, I can tell you that.

These tiny frogs, which inhabit small ponds and stream corridors, are easy to miss if one is not attuned to them. Cricket frogs are most conspicuous in late spring/early summer, when males begin to vocalize. They create a series of surprisingly loud, metallic clicks that are quite un-frog-like. But the vocalizing doesn't last all that long and by now the cricket frogs have fallen silent. The little pond where I made this image probably hosts thousands of individuals, at least at this season. The adult's ranks are supplemented with scores of juveniles, but many/most of those probably won't make it till winter. Lots of potential predators, especially for such a small amphibian. The cricket frog lifespan, if all goes well, is said to only be a year.

PHOTO NOTES: I made this image with my workhouse Canon 100mm f/2.8L macro lens, with the Canon R5 and auxiliary light courtesy of the 600 EX II speedlite. Settings were f/14, ISO 400, and 1/200 second. Camera settings are the least of the cricket frog photographer's issues. As you can surmise from the photo, the tiny frogs blend extraordinarily well with their substrates. That coupled with their small size makes them incredibly easy to overlook. Also, when alarmed, they can leap fantastic distances. No frog that I have firsthand familiarity with leaps as far as a cricket frog in a single bound. We figured they were catapulting themselves some 30x the length of their bodies, maybe more.

The trick is to find a possible subject, slowly ease closer, then slowly drop to the mire and ever so gently worm your way towards the frog. Done with delicacy, one can get quite close - I was probably only a few feet from the animal in the photo. It's best, in my opinion, to have your camera on the ground. Eye level is usually best with small ground-bound organisms.

Some juvenile birds: Tis the season

 

An immature White-eyed Vireo (Vireo griseus) peeks inquisitively from a grape thicket. It was part of a family unit of 3-4 young birds and two adults. I have found this species to be quite curious; nosy, almost. Nonetheless, they typically remain well-concealed in dense growth, peering at objects of interest from within the foliage. White-eyed Vireos are also accomplished mimics and insert snippets of other species' songs and calls into their repertoire. Gray Catbirds, Blue Jays, Willow Flycatchers, Eastern Towhees and other species in earshot are all fodder for copy-catting. This vireo family was in Ross County, Ohio, on August 22, 2024.

This little streaked sparrow might throw one for a loop, especially as this species doesn't hold its juvenile plumage for very long. When the adult arrives to feed the little beggar (2nd photo), its identity is instantly clear. While searching out Thirteen-lined Ground Squirrels in a Ross County cemetery yesterday, I was temporarily distracted by a family unit of Chipping Sparrows (Spizella passerina), the youth noisily exhorting the hard-working parents to bring more food.

In this photo, the adult has a beakful of moths for junior. Chipping Sparrows are wide-ranging and adaptive. I see them in the most urban areas, and also very wild places such as the high West Virginia mountains, and massive alvar fens along the shoreline of Lake Huron in northern Michigan. They are always a welcome sight no matter where they are, as is the dry staccato trill of males. These sparrows were seen and photographed on the same trip as the vireo photo was made.

Thirteen-lined Ground Squirrel

 

The eastern "prairie dog", a Thirteen-lined Ground Squirrel (Ictidomys tridecemlineatus) crouches at the entrance to one of its burrows. Like true prairie dogs, this species is a member of the squirrel family (Sciuridae) and is closely allied to the more westerly prairie dogs. Like the four species of prairie dogs, almost all of the 21 ground squirrel species (formerly in the genus Spermophilus) are westerners. Only the Thirteen-lined Ground Squirrel and Franklin's Ground Squirrel ((Poliocitellus franklinii) range east of the Mississippi River, and the eastern terminus of the Thirteen-lined Ground Squirrel range coincides with the former range of the great prairie ecosystem that once blanketed much of the midwestern U.S. The squirrels make it no further east than central Ohio. Franklin's Ground Squirrel barely makes it as far east as westernmost Indiana.

On August 18, Shauna and I made a run down to a relict ground squirrel population near Lancaster, Ohio. As is often the case, it took a while to let the squirrels adapt to our presence. After a bit, the chap in the previous photo popped up into its sentry posture, the better to view its surroundings. Another squirrel raced around behind it, and we observed another across the road.

This is their habitat: A closely cropped grassy field. Historically, Thirteen-lined Ground Squirrels were probably associated with the 5% or so of Ohio that was original prairie. As that habitat got pulverized with the advent of steel chisel plows - probably 99.9% or so destroyed - I suspect squirrels began to occupy artificial open habitats in those former prairie regions. Even today, the known populations are virtually all in or at least very near to ancestral prairie lands.

At the time of Jack Gottschang's book A Guide to the Mammals of Ohio in 1981, he listed records from 27 of Ohio's 88 counties, although they were likely extirpated from some of those by then, and conversely, were undoubtedly present in many other counties where they were not documented by actual specimens (Gottschang's standard for adequate documentation). Now, the squirrels are surely in far fewer places. There are many sites where there were known colonies, that no longer exist. Human persecution undoubtedly is the culprit in many cases. Ground squirrels and prairie dogs have long been treated as varmints and pests (personal observation: people who freely use the term "varmint" know very little about natural history, and less than nothing about ecology) and eradicated accordingly. Some once thriving colonies, such as the one that occupied the large field at the entrance to Green Lawn Cemetery in Columbus, were exterminated by people, in the latter case, cemetery personal.

Thirteen-lined Ground Squirrels seem to have become scarce enough that formerly listing them at some level of rarity at the level may be warranted. Collection of data on existing populations should be done, to inventory the extent of ground squirrel populations. To that end, if you know of any sites that are still extant, please let me know (locale, at least to the county level, and approximate population size). I can be reached at jimmccormac35 AT gmail.com.

A few random things from recent days, including a beautiful grass

 

A Spring Peeper (Pseudacris crucifer) strikes a pose on a wingstem leaf. Last night was hot, humid, with some showers and lots of the little frogs were out and about. This was at a recently acquired Arc of Appalachia property in Holmes County, Ohio, along Killbuck Creek. Our crew found lots of interesting creatures during our nocturnal foray. The peepers were especially notable, and we saw many. August 8, 2024.

As always, click the image to enlarge

The desiccated corpse of a Long-jawed Orbweaver spider in the genus Tetragnathus is enveloped by a fungal killer, Gibellula pulchra, a fungus that preys on spiders. When a spore lands on a suitable arachnid, the fungus begins to envelope the victim, penetrating it with mycelia that consume its inner tissues. As a last hurrah, the fungus sends out rather showy elongated hyphae that produce spores, thus starting the cycle anew. Shauna Weyrauch spotted this grisly scene on an epic nocturnal foray at a new Arc of Appalachia acquisition. Holmes County, Ohio, August 8, 2024.

A portion of the flowering spike of Side-oats Grama (Bouteloua curtipendula). The orange appendages are the grass's anthers, which contain the pollen. The white feathery objects are the stigmas, which are the pollen receptacles. Rather than evolve fancy flowers to lure insect or other animal pollinators, grasses go for the simpler carpet-bombing strategy. These plants release thousands upon thousands of tiny windborne pollen grains in the hope that some land on the stigmas of other plants and thus cross-pollinate them. The multisyllabic scientific name is a mellifluous delight: Boo-teh-loo-ah ker-tih-pen-do-la. This Side-oats Grama is in my front yard in Worthington, Ohio.

Brown Marmorated Stink Bug (Halyomorpha halys) eggs with freshly emerged nymphs. This pest hails from Asia and was first collected in 1998 in Pennsylvania. Since then, it has spread to nearly if not every state. The first Ohio record dates to 2007 and now they're everywhere around here. One female can apparently lay up to 400 eggs, so the one that dumped these isn't done yet, or she already laid many other eggs. I must admit, there is an artistic symmetry to the bugs/eggs at this stage. My backyard in Worthington, Ohio.

Two upcoming moth programs

Saturday, August 17. Startford Ecological Center, Delaware County, Ohio. 7 - 10 pm.

My coauthor on the Gardening for Moths book, Chelsea Gottfried, will be giving her moth program, then we'll head outside where sheets/light will be set up and luring moths. Stratford has a wide variety of native flora, and it should be very good for moths. Both Chelsea and I will be there for the mothing, which will last for a few hours. This one does have a fee: $25 for adults, $15 for children. The money goes to support the work of this excellent not-for-profit organization. Details are RIGHT HERE.

Saturday, August 24. Fernald Preserve Visitor's Center, Hamilton, Ohio. 7:30 - 11 pm.

I'm giving my talk entitled Mysterious Moths: The Darker Side of Butterflies and following that we'll go check out several nearby mothing stations. The 1,000+ acre site has an interesting history and should produce some noteworthy sightings. This public program is free and open to all.