October 2009

aposematism: WARNING! DO NOT EAT ME!!!

lubber grasshopper flashes and rattles its red wings

This month we will discuss three of our most abundant Refuge insects: the queen butterfly, the zebra long-wing butterfly, and the lubber grasshopper 
 

queen butterfly (related to the monarch)

           zebra long-wing (our state butterfly)


Adult lubber grasshopper 

 


As you can see from the photos, each is strikingly colored to advertise its bad taste and toxicity to predators. Conspicuous colors or patterns are common in the animal kingdom to advertise DANGER. The skunk's black and white pattern advertises the threat of a stinky spray. The coral snake's red, yellow and black rings advertise the threat of a poisonous bite, And the bumblebee's yellow and black pattern advertises the threat of a nasty sting.


In addition to bright color, there is additional evidence that queen butterflies, zebra long-wing butterflies, and lubber grasshoppers are not eaten by predators.

 A group of immature lubber grasshoppers on a sign  A conspicuous zebra long-wing caterpillar
a group of immature lubbe grasshoppers on a sign  a conspicuous zebra long-wing caterpillar

 
POISONS COME FROM THE INSECT'S FOOD PLANTS


Each of our three insect species has evolved ways not to be hurt by poisons that plants have evolved to deter herbivores. The insects even store these poisons to protect themselves from predators. The warning color has the fancy name aposematism. The most famous example is the monarch butterfly, a close relative of our queen butterfly. As Ken Burns has written in his book Biograffitti: 

Up the Food Chain

Things aren't always what they aposeme:
The monarch as a caterpillar eats
Milkweeds, stores their hearty poisons,
And the butterfly defeats
Some portion of an avian predation team
By advertising - with show of color, lack of haste -
That those that dare to peck will find it in bad taste.

We will now see how each of our target species for this month uses a variation on the monarch story with some interesting twists and a few mysteries.

QUEEN BUTTERFLY: Biology and Mysteries

Like the monarch, the queen caterpillars specialize on eating milkweeds. Until this last week this posed a mystery since I had rarely seen the Refuge's one native milkweed, the white vine. I wondered how so many queens could be present when I could find no milkweed even with careful searching. When I did find some milkweed in fall I could not find a single queen caterpillar. Last week I solved part of the mystery when I saw the willows and cattails along the west side of the main canal festooned with white vine milkweed in bloom. In addition a tree island that had been a bird rookery last year was completely covered by milkweed responding to the remaining bird guano.

Tree island covered with white vine milkweed

Close-up of conspicuous flower head
of white vine milkweed

   

Caterpillar of the queen eating milkweed leaf
 

ZEBRA LONG-WING BUTTERFLY: Biology and Mysteries

Our zebra long-wing gets its poisons when its caterpillars eat the poisonous corky passion vine. This food plant is even harder to find than the white vine milkweed because the passion vine has tiny, but very distinctive flowers and tiny blue fruit. Maybe my readers can help me find where these plants grow. One hypothesis is that, like many vines, it only spreads out when it has climbed to a tree-top. So we should look for the vine's distinctive corky stem at or near tree trunks.

 
Distinctive corky stem of passion vine Tiny flower and immature fruit of corky passion vine
Distinctive corky stem of passion vine Tiny flower and immature fruit of corky passion vine
 

Adult zebra long-wings tend to be found in groups in semi-shaded areas and they roost in aggregations at night. The function of this communal roosting may be to teach night-time mammal predators that they are poisonous. Perhaps they have an odor which mammals can detect. In any event if one of the large group is eaten by mistake the predator gets sick and vomits. Thus predators learn their lessons and the rest of the butterflies will then be safe.

A small part of a communal night roost
of zebra long-wings
A small part of a communal night roost of zebra long-wings

A final note about zebra long-wings is that the adult butterflies eat pollen and that allows them to live much longer than other butterflies. Most butterflies sip sugary nectar for quick energy, but nectar is not a complete diet. As shown in the photo, the adult zebra long wing holds a nectar - pollen mix in its tongue where it is slowly digested. Thus the long-wing can use the proteins and fats in the pollen and the sugars in the nectar to get a complete diet and live as long as a year.
 
Nectar - pollen mix on a zebra long wing tongue
Nectar  pollen mix on a zebra long wing tongue 

As with all butterflies, long-wing caterpillars are a stage of the life-cycle that eats and grows. They have a complete metamorphosis from egg to caterpillar to pupa to adult. As Douglas Florian has written: 

You eat, Eat, EAT Miss Caterpillar
Until you are a FATTERPILLAR.
Then change yourself into a pupa
And check out Madame Butterfly, how super!

LUBBER GRASSHOPPERS: Biology and Mysteries

Unlike butterflies, grasshoppers have a gradual metamorphosis with gradual increase in size and little change in shape from smallest nymph to winged adult. Our Refuge lubber is unusual among grasshoppers because its color changes strikingly at the last molt from largest nymph to adult. The immatures are all black with a yellow or red racing stripe and the adults are a variegated mix of orange, brown, black, and green.

Adult and immature lubber grasshopper

Green and orange color forms of adult lubbers

Adult and immature lubber grasshopper Green and orange color forms of adult lubbers

We do not understand why there is a very small frequency of the green form of the adults. And we do not understand why the gregarious immatures are black with a colored racing stripe and the mostly solitary adults are variably colored. Each is a conspicuous color that advertises that the lubber is poisonous.

Another mystery of the lubbers is that in the Louisiana population the adults are all black and readily can be induced to show the wing flashing and rattling display, along with frothing of foul smelling fluid from the wing area. Handling and harassing our adult lubbers rarely causes them to display their bright red wings. Our cat did a better job of eliciting this defensive display and wild mice might be even better.

A western lubber displays as a mouse investigates
A western lubber displays as a mouse investigates 

The mouse probably cannot see the red color of the wings but it can hear the rattling sound and there may be a distinct smell.


A last mystery of the lubber is that they are generalist feeders and not all the plants they eat have obvious toxins that the lubber can tolerate and use for its defense. One year, on a LILA experimental tree island, the lubbers ate almost all of the small planted gumbo limbo and pond apple trees - neither of which has strong smelling leaves that might indicate very poisonous toxins. But lubbers must be eating some poisonous plants because predators do not eat them. In a study on Everglades lubbers, all adults were rejected as prey by 27 different native species of birds, mammals, frogs, and lizards. Often the predator vomited after trying to eat a lubber and then would never try again. On the other hand some non-native species, including marine toads and fire ants, do eat lubbers.

 

REVIEW QUESTIONS

a. Skunks, coral snakes, lubber grasshoppers, and zebra long-wing butterflies have nothing in common.

b.  Monarch butterflies and queen butterflies are closely related taxonomically and ecologically similar.

c. Zebra long-wing butterflies are poisonous but adults are
otherwise similar in diet, flight pattern, and lifespan to all the
other Refuge adult butterflies.