In the natural world predation is relentless, and evading
predators strongly favors the evolution of camouflage colors in
animals. How contradictory then, for small, defenseless creatures -
like red efts and monarch butterflies - to be sporting a bright
shade of orange. But there is more to their cheerful color than
meets the eye. Both the eft and the monarch are poisonous.
Once a predator has tasted one, it soon gets sick, and from that
experience learns not to eat another. Thus, an individual eft or
butterfly may sacrifice itself, but the education of predators
benefits the species as a whole. And, in fact, efts and monarchs
often survive predator attacks. Toads and snakes that swallow red
efts have been observed to vomit up the prey unharmed in about half
Birds that attack monarch butterflies often go for the brightly
colored wings, the most toxic part of the insect. One peck may be
all it takes to deter the bird.
Zoologists call the use of bright colors to warn predators
"aposematism;" generally, the brighter the color, the more toxic
the animal. (The brilliant poison dart frog in South America is a
The orange skin of the red eft contains tarichatoxin, also known
as tetrodotoxin; it's a potent nerve poison. The toxin causes
irritation on contact, and if a lot is eaten, paralysis and death
by suffocation. In experimental studies, snakes that tried to eat
and then spat out a tetrodotoxin-producing newt first rubbed their
gaping mouths on the ground, began writhing, and then exhibited
partial paralysis that required over an hour for recovery. A brief
contact with newt skin was enough to transfer toxin through the
lining of the snakes' throats.
The monarch butterfly's toxin is called cardenolide, and is
derived from a class of plant steroids that is responsible for
livestock poisoning and, paradoxically, is used by doctors to treat
congestive heart failure. Monarchs acquire their toxin from
milkweed, the exclusive food of their caterpillar. (And yes, the
caterpillar is toxic, too.)
Many people don't appreciate that a red eft they see on a moist
forest floor is the larval stage of the aquatic eastern newt.
Eastern newts are toxic, too, albeit only one tenth as toxic as
efts, but it is enough. Because they are poisonous they can share
waters with predatory fish. By contrast, the aquatic life stages of
other eastern salamanders, all of which lack toxins, are largely
restricted to vernal pools where fish can't live.
Predators remember the experience of eating an eft or monarch
for some time.
So effective is this learning that various unpalatable species
have evolved to resemble each other. Among butterflies, the viceroy
looks strikingly like a smaller version of the monarch. The viceroy
tastes bad because its larvae feed on willow, a source of salicylic
acid, the active ingredient in aspirin. The salicylic acid in
viceroy butterflies makes them bitter and irritates the stomachs of
predators. Both viceroys and monarchs are orange with black stripes
and are avoided equally by predators.
While there are no mimics of the red eft, there is a western
U.S. salamander, the yellow-eyed Ensatina, which closely resembles
the dangerously toxic coast range newt. Both have orange skin
coloration and yellow eye patches.
There's even evidence of a toxin 'arms race.' Out west, some
populations of garter snake have evolved a degree of resistance to
tetrodotoxin, allowing them to eat toxic newts with few side
effects. This has led to the evolution of higher tetrodotoxin
levels in the newts that live where the resistant snakes are
One wonders why the toxin of newts and efts does not harm the
animal itself. That question was answered when researchers
discovered a mutation that makes the eft's nerve cells immune to
tetrodotoxin. It comes with a price: sluggish transmission of nerve
impulses. But what does it matter if efts are slow-moving? They
don't need speed.
Li Shen is an adjunct professor at the
Dartmouth Medical School and the chair of the Thetford, Vermont,
Conservation Commission. The Outside Story is assigned and edited
by Northern Woodlands magazine and sponsored by the Wellborn
Ecology Fund of New Hampshire Charitable Foundation.