Sharing the Risks and Dividing the Dangers

A quote from the preamble to the U.S. Constitution sums up the idea of Müllerian mimicry very well – "We the people ... in order to ... provide for the common defense, promote the general welfare ..."

Müllerian mimicry is named in honour of the German naturalist Fritz Müller, who first observed and offered an explanation for the phenomenon. Simply put, several species, not necessarily related, that have predators in common will also tend to mimic each other and share aposematic colors or warning signals. Of course, unlike the U.S. model there's no conscious or intelligent decision to co-operate, and the mutations that eventually give rise to a given defensive game plan are random – but the process of natural selection is not. A given shared color scheme benefits and promotes the survival of all the individuals within the species that share it, and it's survivors that (naturally!) hand their genes down for another roll of the dice to the next generation.

Members of the order Hymenoptera that can sting tend to exhibit bold black-and-yellow stripes. A child, a bird, or a frog that has been stung by a Honeybee will likely remember the painful experience and in future also avoid a Bumblebee, a Paper Wasp and a Mason Wasp – the individual Honeybee (a non-reproductive worker in any event) loses, but its relatives and the other Hymenopteran species gain a measure of immunity from predation.

Beetles belonging to the family Coccinellidae, better known as Ladybird Beetles or Ladybugs, secrete toxic alkaloids to discourage predators, exuding fluid from their leg joints if threatened. The colors and patterns of many species are variations on a similar black-and-red theme, and not surprisingly, their family name is derived from the Latin word for scarlet.

Three-Banded Lady Beetle (Coccinella trifasciata perplexa)

A mating pair of Polished Lady Beetles (Cycloneda munda)

Convergent Ladybird (Hippodamia convergens)

Glacial Ladybird (Hippodamia glacialis glacialis)

Milkweeds produce cardiac glycosides to ward off insects, but over time a diverse assortment of insect species have adapted and appropriated the milkweed's chemical defense for their own protection. Such insects sequester the toxins in their own bodies and boldly advertise their noxious natures with a combination of showy black and red/orange colors.

The well-known Monarch (Danaus plexippus)

Small Milkweed Bug (Lygaeus kalmii)

Large Milkweed Bug (Oncopeltus fasciatus)

Larvae of the Milkweed Tussock Moth (Euchaetes egle) ... a group of these caterpillars can annihilate a leaf, within a short time there's little left but the veins and frass.

Red Milkweed Beetles (Tetraopes tetrophthalmus) – their scientific name, derived from Greek, means four eyes. Apropos, as their antennae arise in a manner that divides their compound eyes into a pair of eyes above and below the antennae. And in the background it looks like there's an exception to the black-and-red milkweed color rule, a tiny Monarch caterpillar.

Another image of the Monarch larva, and that's nature for you ... as soon as you think you've found a rule or underlying logical principle, there's a departure or deviation that challenges your assumptions as to how things work.

On the other hand – Monarch caterpillars aren't toxic from the get-go when they hatch, they acquire their bad taste over time as they consume milkweed leaves. It's been my observation that the yellow, white and black stripes on the tiny first instar larvae are indistinct and blend together to form green, thus camouflaging the caterpillars while they are still vulnerable to predators. And the strongly marked later instars do in fact possess the black-and-yellow aposematic warning scheme common to many Hymenoptera. So it seems that the Monarch participates in two different Müllerian defensive strategies throughout its life cycle.

Heads or Tails?

In spite of its psychedelic complexion and robust build this Promethea Moth (Callosamia promethea) proved difficult to spot amongst the foliage.

I've inserted my pinky finger in the picture to give an idea of the size of this insect, but it's scared and has hunched itself up somewhat, making it about ten centimeters shorter than its normal length ... about the same as my finger.

Chowing down on some yummy White Ash leaves ...

Note in the images above that the head has no bold colors or patterns, and the insect pulls it under its body when it feels threatened. Now consider these views with an emphasis on the posterior end. The terminal pro-legs or pseudopods are large, bear a black circular mark that suggests an eye, and are left in plain sight. (Pseudopod → "false foot" ... insects have only six legs, they are visible just behind the head in this photo).

Eyes can betray an animal's position to a potential predator, and many organisms sport bars or camouflage patterns to disguise them. By the same token, note how many butterflies, fish, etc., often sport fake eyespots on hindwings or tail fins. Are the eyespots targets to draw a strike to a non-vital area, or to make an otherwise innocuous species look threatening to a hungry hunter? Here's some thought-provoking reading: Why eyespots?.

And where, you say, is the "moth" in these photos? That lies in the future ... first, this caterpillar will overwinter as a pupa, and with luck this story will continue next year ...

The Orange-Humped Mapleworm Moth (Symmerista leucitys) adopts similar "false head" plan of action if it feels endangered. Although the head is a bold shade of orange the back end also bears prominently colored red and orange markings, and it holds its posterior the air with the last pair of prolegs splayed open. Everything about the caterpillar's posture suggests a head with antennae – at the non-vital backside of the insect.

The two appendages at the tail end of this Furcula Moth (not sure what species) larva also look very much like antennae.

The slow moving, soft-bodied larva of the larva of the White Admiral (Limenitis arthemis) makes a yummy morsel for a hungry bird. This caterpillar increases its chances of survival by not only being colored like ...

... but adopting the posture of, an inedible and not-so-tasty bird dropping.

Some species make themselves distasteful or toxic to minimise predation. The larva of the Monarch (Danaus plexippus) ingests the toxins found in its food plant, the Common Milkweed. The caterpillar's bold yellow, white and black stripes advertise its unpalatability.

Presumably the Milkweed Tussock Moth (Euchaetes egle) also toxic for the same reason, and hair or bristles can also be a deterrent to being captured and swallowed. But what's with the grouping? Are they mimicking a larger animal? Or is it a matter of safety in numbers like a flock of birds or a school of fish ... any single individual is less likely to be targeted?

Metamorphosis

The Dogday Harvestfly (Tibicen canicularis) goes through incomplete metamorphosis, having only three stages in its life cycle: egg, nymph and adult. The nymphs live underground sucking juices from tree roots, preferably pine trees.

After three years the nymphs emerge and go through their final molt, changing into winged adults. The cast off exoskeleton may be seen in the picture below. As is the case with many insects the adult cicada does not eat; it lives long enough to reproduce and then dies.

It's going to take a bit of luck to get a shot of an adult cicada as they tend to spend their time high up in the trees.

Dragonflies also go through incomplete metamorphosis, spending the second stage of their life living a predatory aquatic existence. This discarded nymphal exoskeleton (exuviae) is about 2½ inches long and likely belonged to a skimmer or a darner.

The Monarch Butterfly (Danaus plexippus) goes through complete metamorphosis ... egg, larva, pupa and adult. The larva in following image is feeding on Swamp Milkweed and this one seemed to have a marked preference for the seed pods. The caterpillar ingests toxins present in the sap of the milkweed plant and the bold colors advertise its poisonous nature.

I'm going to be keeping an eye out because this caterpillar looks like it will be ready to pupate any day and this looks like a good opportunity to make a photo essay of the change from larva to adult.

These are the seed pods the caterpillar ate in only two days ...

... and it's moved on to the leaves and still going strong!

Unless I find another caterpillar it looks this photo study of a larva metamorphosing into an adult Monarch won't be finished.

I checked out the caterpillar the following morning; it was torpid and looked like it was ready to pupate. Two hours later ... it was gone. Maybe a bird got it. Birds have to learn to avoid the warning colors and it seems like one might have tested its luck.