Devil’s-Potato and Its Mimectic Moths

Echites umbellata

(Echis is a genus of nasty old vipers.  Echites vines look snakey, and maybe because of that have a history as  snakebite remedies.  An umbel is a type of flower arrangement.)

Apocynaceae

A Google book report is a crummy blog, and this week is honestly nothing more.  I did not set out to compile Google notes, but rather was curious about pollination in the exquisite Devil’s-Potato flower which looks like a cultivated white Mandevilla (Dipladenia) Vine. Trying to find the pollinator online took me down the rabbit hole into Alice in Mothland, complete with a large caterpillar.

Devil’s Potato by John Bradford

Before the moths comes context.  The Devil in the name comes from deadly sap, no surprise in the Apocynaceae Family.  In Jamaica the vine applied superficially to a leg pain caused vomiting transdermally.  Poison’s a good thing for immune moth larvae whose feeding makes them too poisonous to predate.

The fruit is a T-shaped double pod having two long horns joined in the middle.   The “potato” is a thick rootstock this tough vine uses to survive on stormy coastal dunes from Central America and the Caribbean to Florida.

T-shaped two-horned pod

The flower is a classic textbook moth-pollinated blossom, having white coloration, a striking fancy silhouette visible at night, long narrow flower tube, and fragrance.   At mid day there is no fragrance;  at about 6 pm it is perfumed.    You’d think looking up the mothy visitor would be a no-brainer.  Tried hard yet still don’t know, but it is all about the journey.

Can’t miss that silhouette, even at night. Note the narrow entrance for the moth proboscis.

Echites is intimate with at least three moth species.   John and I don’t have photos of them, but revealing links are at your fingertips below.   Here are the three moth-keteers:

1. Uncle Sam Moth, aka Faithful Beauty (Composia fidelissima)

CLICK to see it

A patriotic beauty!  As with all three moths featured today, its larva feeds prominently on Echites umbellata, extending to other related members of the Apocynaceae, including horticultural Oleander as do the two other moths.   The moth also uses Baybean, a legume vine literally intertwined with Devil’s Potato.   Baybean has wicked poisons of its own.  Unlike most nectar-feeding moths, Uncle Sam is active by day.  Otherwise its 4^th of July colors would be wasted.   A superficial impression is that this moth visits flowers smaller than Devil’s Potato, and the evening floral fragrance indicates a nocturnal or twilight moth. Therefore  I vote against it as the mystery pollinator.

  2. Oleander Moth, aka Polka Dot Wasp Moth (Syntomeida epilais)

CLICK for a peek

The Oleander Moth looks like a fearsome wasp, but is really a harmless poser.   It is poorly named, as Oleanders are horticultural introductions, and the caterpillar apparently expanded to Oleander from our native Echitites umbellata as its original larval host in Florida, probably also frangini (Plumeria) where those are native..   Closely related, Echites, Plumeria, and Oleander no doubt feature similar toxins. This polka-dotted moth with color similarity to Uncle Sam uses ultrasound to attract a mate.  The female emits a sound inaudible to you and to me,  and the male moth comes running like match.com.

That the Oleander Moth has warning coloration and the appearance of a wasp is noteworthy, but the mimicry runs deeper, again to ultrasonic signals serving not just to lure mates, but additionally to warn off moth-eating ultra-sound-navigating bats who would not see colors or waspy wings, but get the message sonically.   As with visually mimicry, moth resembling wasp, there are moths who mimic the sound warnings of other moths.

These moths have layered lines of defense: poisons, warning coloration and wasp appearance to deter birds by day as well as ultrasound warnings to deter bats in the dark.

As with Uncle Sam, the Oleander adult seems too small and too day-active to be the pollinator.  I vote nay.

3. Tetrio Sphinx Moth (Pseudosphinx tetrio)

CLICK

Speaking of mimicry,  another caterpillar with Devil’s Potato as predominant or prominent native larval host, now expanded to Oleander,, is the Tetrio Sphinx (aka Frangipani Hornworm) Moth.   The huge caterpillar has red, yellow, and black warning coloration.  Those colors remind you of any sneaky snakes?  Ecoogist Dan Janzen suggested the caterpillar mimics a coral snake, not only in coloration, but also in a writhing and biting behavior when grabbed.

The caterpillar morphs into a large adult sphinx moth that seems just right to be the pollinator we seek.   With no data in support beyond circumstantial speculation, it gets my vote:  size match seems ok, and this moth is twilight/nocturnal.   The photo below shows the opened flower, with the entrance to the flower tube at the right, and a device to block penetration by anything other than a moth proboscis to the left.  To get from the entrance past that barricade on the left down (leftward) into the nectar, the proboscis must exceed 30 mm.   The length recorded for the Tetrio Sphinx is 49 mm, perfect.  If it is the pollination agent,  it is a handy example of a pollinator whose larval stage lives on the species it grows up to pollinate.   This is known well enough in other species pairs, such as yucca moths and the beetles that pollinate coontie.

Opened flower tube. Entrance at right.  Conical barricade at left has visible slits a moth proboscis can penetrate.  The proboscis must exceed 30 mm.  Average for the Tetrio Sphinx Moth is 49 mm.

A final odd note.  In Southeast Florida Devil’s Potato Vine is no longer abundant, as its favored habitats have become seaside condos even though at least three different moth species probably depended partly or entirely on it.   As the habitat goes, the vines go, and so go the moths…right?  Such a typical finger-wagging ending..eh?  But hold on.   Looks like all three fickle moths have taken up with cultivated Oleander.  Gotta be a lesson there.