Bug o’the Week – Argus Tortoise Beetle

Greetings, BugFans,

The BugLady’s first thought when she glanced at this beetle was that it was a Swamp milkweed leaf beetle (which, for perching purposes, doesn’t restrict itself to swamp milkweed).  Note to self – always look twice.  Although their markings are similar, this beetle is not as “leggy” as the SMLB, and so it seems to sit closer to the substrate.

Every few years, she finds a new (to her) species of tortoise beetle – we have visited them in the form of Mottled, Horsemint, and Thistle tortoise beetles – and while the adults are interesting, it’s the larvae that blow her away.  Fecal shields? Faeciforks?

Argus tortoise beetles (Chelymorpha cassidea) are in the huge leaf beetle family Chrysomelidae.  “Chelymorpha” means “turtle/tortoise-form,” and “cassid” means “helmet.”  According to Wikipedia, “The name Argus comes from the mythical Greek giant Argus Panoptes, who was sometimes depicted with 100 eyes, because the beetle is able to stretch out its red head beyond its pronotum [the front end of its thorax], as if it were a single red eye.”  Maybe a little poetic license going on, there https://bugguide.net/node/view/1286837/bgimage.

At about one- third of an inch long, it is one of the larger Chrysomelids, and it comes in various shades of orange, with heavier or lighter spotting https://bugguide.net/node/view/1608007/bgimage, https://bugguide.net/node/view/1456941/bgimage, and https://bugguide.net/node/view/274124/bgimage, and newly emerged beetles are pale for a few days until their color develops https://bugguide.net/node/view/1080775/bgimage.  The edges of the thorax and abdomen sweep out a little, like a tiny skirt, giving the adult a suction-cup-like appearance and protecting its underpinnings from ants.  The books say that its head slants backward, which we usually can’t see because it’s hidden under the prothorax.

Females lay eggs in clusters on the leaves of host plants, members of the bindweed family Convolvulaceae https://bugguide.net/node/view/285461.  The larvae https://bugguide.net/node/view/676256/bgimage feed on the leaves gregariously for a while https://bugguide.net/node/view/274128 before going their separate ways.  A few sources say that they drop down and overwinter on the ground as pupae, but others show pupal cases on green leaves https://bugguide.net/node/view/299697 and say that they emerge in about 10 days and overwinter as adults.

An alternate common name is the Milkweed tortoise beetle, though they don’t feed on milkweed (in 1887, an entomologist named Lintner referred to them as a “milkweed beetle with bad habits”).  The bindweed family includes some domesticated species like morning glories and sweet potatoes, so this is a beetle that is on our radar.  Some sources say that it can do damage to the plant, and others say that the plants recover readily unless they are seedlings.  There are historical records of the Argus tortoise beetle on raspberry, blackberry, rose, and peas, too, but the beetles may simply have been enjoying the view.

Morning glory, hedge bindweed, and field bindweed leaves discourage grazing by manufacturing poisonous alkaloids that the Argus tortoise beetle sequesters in its body to protect itself, in turn, against predators (that’s why the beetle can get away with its eye-catching orange and black coloration).  Not 100% successfully, though – the beetle has several egg and larval parasites, and in an article published in 1889, Frank Hurlbut Chittenden wrote that “The Biological Survey has found the Argus tortoise beetle in the stomachs of 14 species of birds , most often in those of the starling ( Sturnus vulgaris ).”

Brief botanical aside: Field and Hedge bindweeds are lovely, white/pale pink-flowered wild morning glories of edges and grasslands whose slender vines sprawl on sturdier plants.  They’re not native.  The problem is their root system, which is massive, with deep taproots and with rhizomes that may extend eight or more feet from the plant.  So, while the delicate vine and leaves climb over sturdier plants, robbing them of sunshine, the roots are hogging the water, and a small piece of root thrown up by a plow can grow into a new plant.  Although its dietary attentions do stray, the Argus tortoise beetle is being viewed as a biological control for bindweeds.

The cool thing about the Argus tortoise beetle is the way its larvae protect themselves.  Some insects distance themselves from their droppings (frass) because predators and parasites can track them by its odor.  Not so the tortoise beetle.  Like other tortoise beetles, the Argus tortoise beetle larva embraces its poop, saving it and fashioning it into a fecal shield, a tiny “umbrella” of frass impaled on the forked tip of its abdomen (faecifork).  This it waves around or shelters under when it feels threatened, providing its predators a “what the heck!!!” moment.  https://bugguide.net/node/view/567526 https://bugguide.net/node/view/676255/bgimage.

Brief excretory aside: The frass of skipper butterfly caterpillars, studied by a scientist who calls herself an “Evolutionary faecologist,” is expelled under pressure, like a tiny cannonball.  One blogger calls it “ballistic pooping.”  The frass pellet of the Silver-spotted Skipper may land 38 body lengths away https://www.sciencemag.org/news/2003/03/frass-flies.

Adults defend themselves in classic Leaf beetle fashion – they drop down and, says Chittenden “play possum,” and for that reason do not very often find their way into the collecting net.”

When she’s researching insects, the BugLady takes note of the hits, both sacred and profane.  Lots of photography sites for this beetle, and FYI, Walmart sells a handsome Argus tortoise beetle poster.

Kate Redmond, The BugLady