JIM CONRAD'S
NATURALIST NEWSLETTER
Issued in Río Lagartos, on the northern coast of
Yucatán, MÉXICO
in Ría Lagartos Biosphere Reserve

December 21, 2014

MUD TURTLE
On the highway he looked like something fallen from a car engine so when I circled the bike to take a look I nudged him with my foot, thinking I'd hear a metallic scrape, but instead there was a hollow sound, like something hard with guts inside. Then I noticed that he was wet and covered with algae. He was a turtle, and he needed saving from the next car coming along. You can see him in his closed-up shell safe on the ground next to a pond away from the road at http://www.backyardnature.net/n/14/141221tt.jpg.

The shell was higher and narrower than those of most turtles. At the far left side of the above picture, notice the nose beginning to poke from the shell. That's a particularly narrow and pointy nose. That and his narrow, high shell and his stinky smell were good field marks, but I still wanted to see the rest of his body for a solid identification.

Theoretically a human can outwait any turtle withdrawn into his shell, but that's without mosquitoes. As I waited and his head poked more and more from his shell, dozens of mosquitoes settled on me. The moment I'd brush them off, in would go his head. After several attempts at waiting for him to completely come out my best shot, still not showing much, was the one shown at http://www.backyardnature.net/n/14/141221tu.jpg.

That's enough, though, to see the whitish lower lip, which is an important feature. Eventually it became clear that the mosquitoes were going to win, so I just flipped him over to get a good shot of the scale, or "scute," pattern on his lower surface, his plastron, shown at http://www.backyardnature.net/n/14/141221tv.jpg.

Mainly by comparing the plastron's scute pattern with pictures of turtle plastrons on the Internet, our little highway turtle revealed himself to be a White-lipped Mud Turtle, KINOSTERNON LEUCOSTOMUM, found from southern Mexico south through Central America into northern South America as far as Ecuador.

White-lipped Mud Turtles mostly occur in humid, swampy areas with standing or very slowly moving water, including brackish water. They feed on insects, mollusks, dead fish and other carrion, and sometimes fruit and other plant matter.

*****

WINGED OYSTER
A bivalve shell washed onto shore on the Gulf of Mexico beach across the estuary from Río Lagartos. It's shown at http://www.backyardnature.net/n/14/141221pt.jpg.

Its background color with blotches of pearly luster are reminiscent of oyster shells, but oyster shells don't have that fingerlike projection shown at the picture's top, left corner. What we have here is one of several species known as winged oysters. It's the Atlantic Winged Oyster, PTERIA COLYMBUS. In older individuals, the left-pointing wing becomes longer.

Atlantic Winged Oysters occur in the Western Atlantic in waters between ten and a hundred feet deep (3-30m) from North Carolina on the US Atlantic coast south through the Gulf of Mexico and Caribbean to Venezuela and northern Brazil. Often they're found attached to stems of gorgonian corals by strong filaments that some kinds of mollusks are able to secrete, called "byssus threads." Atlantic Winged Oysters often host algae and other organisms on their shells, which camouflage it. They filter algae and other organisms from water circulating around them.

Sometimes certain winged oyster species are called winged pearl oysters because they can produce pearls and are cultivated for that purpose. Studies indicate that with proper culture our Atlantic Winged Oyster might produce pearls of a size and quality equal to pearls produced commercially in Japan and Australia, where commercial pearl culture is most developed.

*****

PYGMY KINGFISHER
Back in 2011 a Pygmy Kingfisher landed right beside me as I'd sat on a pond bank on the Caribbean coast, and I'd thought that that was my once-in-a-lifetime chance to get a picture of that House-Sparrow-size species. You can see the photo at http://www.backyardnature.net/yucatan/pyg-king.htm.

That's a shot from behind. This week another one gave me the side view shown at http://www.backyardnature.net/n/14/141221kf.jpg.

I'm getting the impression that Pygmy Kingfishers may not turn up often, but when they do appear they're not as shy as most birds. If they want to perch someplace they'll do so whether there's a fellow with a camera nearby or not. I've seen this week's individual several times in the same place, a little freshwater "petén," or spring-pond, in the mangrove zone, but usually he perches where it's too shadowy for good photos. This week's bird is female, for the adult male lacks the dark, speckled chest band.

Pygmy Kingfishers occur from southern Mexico south to Ecuador and Brazil.

*****

TARANTULA HAWK
When you're out birding with your mind alert for movements of things of a certain size, down here there's this big insect that again and again makes you think you're seeing a hummingbird. It flies with its long back legs dangling behind, at first looking like a Mexican Sheartail with its long tail. It happens all the time and all these false alerts are frustrating. For years I've been trying to photograph the insect so I could figure out who it is, but it's fast moving and I've seldom seen it land.

But this week in a large roadside population of flowering Waltheria americana several of these hummingbird-mimickers were busy feeding on flower pollen and finally I got some pictures. One is shown at http://www.backyardnature.net/n/14/141221th.jpg.

Obviously it's a wasp, and a big one, nearly 2 inches long (5cm). Basically it's black, with blue iridescence coming and going as the wasp moves about. Another shot from above the wasp, showing the wing venation for good identification, is at http://www.backyardnature.net/n/14/141221ti.jpg.

Another shot, a bit blurry but displaying an important feature, is at http://www.backyardnature.net/n/14/141221tj.jpg.

That shows the folded-back wings' lower surface, and it appears that each wing has a white band at its tip, and another a little below it. However, remember that wasps have four wings. I'm interpreting what appears to the be the second white band on each wing as tips of the lower pair of wings. The description of the species I think this is says that all four wings are completely black except for their white wingtips.

I'm calling this the Mexican Tarantula Hawk, PEPSIS MEXICANA, occurring in arid areas from the southwestern US near Mexico south into Costa Rica. I think we've met this wasp before, on the Caribbean coast north of Mahahual, pulling along a tarantula it had just paralyzed with a sting. You can see and read about that dramatic event about halfway down our Mexican Redrump Tarantula page at http://www.backyardnature.net/mexnat/redrump.htm.

The tarantula hawk wasp in those photos isn't planning to eat the tarantula itself. Adult tarantula hawk wasps, like our roadside ones among the Waltherias, feed on pollen and nectar. However, their larvae do eat tarantulas. Here's the story:

When an adult female tarantula hawk wasp is ready to lay an egg, it locates a tarantula by smell, possibly having to enter the tarantula's burrow to drag it out, and then the wasp may need to wrestle with the tarantula it until it can deliver a sting. The sting paralyzes the tarantula almost immediately, and the tarantula stays paralyzed for the rest of its sad life. The paralyzed tarantula is dragged into a burrow the wasp has dug into the ground, the wasp lays her egg with the tarantula, and the chamber is sealed. When the egg hatches, the tiny larva immediately begins feeding on it. The tarantula remains alive, but paralyzed, until the final stages of the larva's growth.

Tarantula hawk wasps also sting humans and their stings are regarded as among the most painful of all insect stings. However, they're not dangerous unless you have a special sensitivity. Happily, the wasps aren't aggressive toward humans, and sting only when aggressively provoked.

Tarantula hawks can be hard to identify, and there's a second genus, Hemipepsis, that looks very much like our Pepsis. However, the strong iridescence and pale wingtips of an otherwise all-black wasp point to this species. Also, distribution maps disqualify other Pepsis species treated in CR Vardy's 2000 work, "The New World tarantula-hawk wasp genus Pepsis Fabricius (Hymenoptera: Pompilidae)," which can be downloaded for free at http://www.repository.naturalis.nl/document/46285.

*****

ORANGE BRANCHING SPONGE
On the Gulf of Mexico side of the thin finger of land separating Ría Lagartos Estuary from the sea, a norte's waves had washed up the pretty, orange, branching sponge shown at http://www.backyardnature.net/n/14/141221sq.jpg.

It was a firm sponge, not soft and yielding as you expect a sponge to be. A close-up of the sponge's porous surface, an oscule (large opening), and its surface "hairiness" consisting of short, sharp, protective spicules, is shown at http://www.backyardnature.net/n/14/141221sp.jpg.

At http://www.spongeguide.org I used the "Find a Sponge" feature on the right side of the entry page to identify our sponge. These are the features chosen to get the name: Color, orange; consistency, tough; morphology, branching, and; habitat, rocky shore/shallow reef.

The search led to CLATHRIA (THALYSIAS) VIRGULTOSA, found in mangroves, coral reefs and on shallow rocky bottoms throughout the Caribbean and Gulf of Mexico. It has no commonly used name, though "Caribbean Orange Branched Sponge" would make a good one.

On the Internet, specialists describe the taxonomy of this sponge as a mess, as indicated by the (Thalysias) normally inserted in the binomial's center. Part of the problem is that this species can change its form, depending on how physically rough its environment is. In shallow to exposed waters buffeted by waves and where tidal currents are strong, our cylindrical, slender, branched sponge grows like a thick crust.

Little information is available about this species. Most sea sponges are "detrivorous," meaning that they filter out organic debris and various microbes from water circulating around them and it looks like that's what our sponge does.

Remember that a sponge is a single animal, not a colony of tiny ones.

*****

CORMORANT ON A SIGN
Here and there in Ría Lagartos Estuary there are signs standing in open water explaining things to visitors in tour boats, and often one or more birds are picturesquely perched on the signs, usually pelicans, gulls, terns and cormorants.

The other day our boatload of visitors from Poland wanted a closer look at a cormorant. As we approached, the cormorant spread his wings, providing the interesting picture at http://www.backyardnature.net/n/14/141221cm.jpg.

Of course cormorants often spread their wings exactly like this, to dry them against the sun and warm up, but it was interesting that this bird did it just as our boat was approaching so close that everyone expected the bird to fly instead.

I think it was a matter of "displacement behavior," which is usually thought of as self-grooming, touching, or scratching done when an animal, such as a cormorant or a human, is caught in a conflict between two drives. In this case, probably the bird both wanted to fly because he was getting nervous, but also wanted to stay, because flying away and getting all wet again is a drag. When a person experiences such conflicts, maybe he or she scratches the head or coughs.

Whatever the reason for spreading its wings, that's a Double-crested Cormorant, PHALACROCORAX AURITUS, the one commonly seen in much of North America, though in most inland locations only during summers and during migrations. Here they are just non-breeding winter visitors. We do have similar looking but smaller Neotropic Cormorants who stay here year round, though. You can tell that this is a Double-crested by the configuration of the fleshy area behind its bill. Notice the fleshy part between the eye and top of the bill. You can compare that with our Neotropic Cormorant at http://www.backyardnature.net/yucatan/cormoran.htm.

****

MAREÑA, THE SEACOAST BEAUTY
Nowadays the little road following the coast just south of Río Lagartos is beautified by the presence of a dense, small tree with dark green leaves and abundant yellow blossoms, as shown at http://www.backyardnature.net/n/14/141221cv.jpg.

The thumbnail-size yellow flowers are arranged in a clutter of lanky racemes bunched at branch tips in the manner shown at http://www.backyardnature.net/n/14/141221cw.jpg.

That picture shows that the foliage consists of compound leaves divided into fairly large, roundish leaflets. One of the twice-compound leaves with its leaflets broadly rounded and notched at their tips instead of ending in sharp points is shown at http://www.backyardnature.net/n/14/141221cx.jpg.

Seeing such a twice-compound leaf on a tree, the first plant family to come to mind is naturally the big Bean Family, so at this point in our analysis of who this tree might be we begin looking for other Bean Family features. A glance at the flowers leaves us a little hesitant, as you can see at http://www.backyardnature.net/n/14/141221cy.jpg.

If the flower had been of the classic Bean Family "papilionaceous" kind -- with large upper petal, two side petals, and the two lower petals fused along their common margins into a scoop-like shape, and with stamen filaments united into a cylinder around the ovary's style -- we'd have absolute confidence that our tree belongs to the Bean Family. However, the sepals, which in most flowers are small and green, here are large and yellow like the petals, plus the petals are only vaguely papilionaceous, and the stamens don't have their filaments united into a cylinder.

And yet, the pretty roadside tree is in fact a member of the Bean Family. It belongs to that minority of Bean Family species segregated into the subdivision, or subfamily, of species with flowers similar to ours -- flowers that can give the impression of exhibiting a transitional state between the bilaterally symmetrical, papilionaceous flowers of most Bean Family species, and flowers in other plant families whose flowers show radial symmetry. The Bean Family subfamily our roadside tree belongs to is the Caesalpinia Subfamily, the Caesalpinioideae.

Our roadside tree is itself a member of the genus Caesalpinia, the large and important genus providing the subfamily its name. It's CAESALPINIA VESICARIA, in Mexico occurring only in the Yucatan Peninsula, but extending beyond the Yucatan through the Caribbean and south to Costa Rica. There's no good English name for the tree but in the Yucatan it's called Mareña, meaning something like "She, of the sea."

"Mar" is "sea," and the suffix "-eña" means "coming from, related to, or like." The tree is so pretty that it's sometimes sold as a tropical ornamental under the name Large-leaved Caesalpinia, but that's such an anemic handle that we can't let it displace the lovely "Mareña."

In the Bahamas, Mareña has been used medicinally to treat low blood pressure, and at one time the wood was exported to the US as a source of reddish dye. Some freshly splintered stems from a Mareña soaked for two days in water at room temperature produced the reddish brew shown at http://www.backyardnature.net/n/14/141221cu.jpg.

If I'd boiled fresh heartwood maybe the color would have been more vivid. Mareña wood's tinted water isn't as bright as some colors we've tested the same way, but still it's a color and back when humanity was hungry for textiles colored other than dingy gray, Mareña's reddish dye must have been appreciated.

*****

WIDGEONGRASS
I'd never seen the estuary's water so low, thanks to an especially low tide. Vast acreages of what's usually open water now was brown, leafy aquatic vegetation waiting for the tide to return. As our flamingo-viewing boat positioned for a better look at a big crocodile, I could see that in the shallow water next to the boat the bed was thickly mantled with grass-like vegetation. Plants retrieved from the water were weakly rooted to the floor, and out of the water looked like nothing more than wet crabgrass. You can see the tangled mess at http://www.backyardnature.net/n/14/141221ru.jpg.

A close look reveals certain features pointing to its identity. For example, one stem bore what's shown at http://www.backyardnature.net/n/14/141221rz.jpg.

That shows a stem and a flower emerging from between wrap-around "sheathes" flaring at the bottom of two wiry leaves. The flower looks like four stacked hamburger buns inside a long, pointy bladder. The bladder is formed by undeveloped leaf sheathes of unexpanded leaves that later will spread above the flower. The flower bears two stamens, each stamen with two anthers, all four anthers in a line and looking like they're split across their middles, which is the fracture line where the anther will split to release pollen. Through the bladdery sheathes we can't see the female parts but they're there.

Once the flower is pollinated, the stem, or "peduncle," below it elongates and the spent anthers fall away. You can see ovaries of pollinated flowers on a fast-lengthening peduncle at http://www.backyardnature.net/n/14/141221ry.jpg.

The peduncle lengthens considerably. I read that eventually it curls until it forms up to five coils, but ours only makes a weak effort at one coil -- maybe because the fruits aren't yet mature -- as you can see at http://www.backyardnature.net/n/14/141221rw.jpg.

A close-up of two immature fruits is at http://www.backyardnature.net/n/14/141221rx.jpg.

This plant, usually called Widgeongrass but also Ditchgrass, is RUPPIA MARITIMA, found in shallow waters of brackish streams, lagoons, estuaries, ditches, and lakes along ocean shores practically worldwide, except in the polar zone. It's a monocotyledonous plant like grasses, lilies and orchids. Despite the "grass" part of its common names it isn't a member of the Grass Family but rather belongs to its own family, the Widgeongrass Family, the Ruppiaceae. The Widgeongrass Family is a small one embracing only one genus and about ten species, all growing submersed in brackish or saline waters, or fresh waters with very high calcium or sulfur ion concentrations.

I was especially tickled to meet this plant because in recent Newsletters we've been looking at the extremely important seagrasses that form dense underwater prairies offshore here and in the estuary. Seagrasses hold the sea or lagoon floor in place with their roots, and provide food and protective cover for untold numbers of aquatic animals. In this area ecologist list four main seagrass species. So far we've profiled three of those, and now this Widgeongrass is our fourth. The other three are Manatee-grass, Turtlegrass and Shoal Grass. You can review these under our "Aquatic" section at http://www.backyardnature.net/yucatan/seashore.htm.

Widgeongrass, despite its species name of "marina," is best described as a salt-tolerant freshwater species. The plant often self-pollinates, but the flowers also release pollen that reaches other plants by floating away on bubbles. The drupelet-type fruits -- drupelets being a part of an aggregate fruit such as raspberries and blackberries -- are dispersed inside the guts of fish and waterbirds that eat them. The plant also reproduces vegetatively by sprouting from its rhizome to form colonies.

Widgeongrass is so important to aquatic habitats such as our Ría Lagartos Estuary that in many cases wetland restoration begins with the recovery and protection of this plant.

*****

BURHEAD #2
Last week we looked at a local aquatic plant called Burhead. It was Echinodorus subalatas, and you can see its leaves looking like those of North America's lawn weed known as the Narrow-leafed Plantain, at http://www.backyardnature.net/yucatan/burhead.htm.

This week in a shallow pond along the road through the marsh between Río Lagartos and San Felipe another aquatic plant turned up with white-petaled blossoms very similar to last week's Burhead, but this one's leaves were much broader and had rounded lower lobes, as shown at http://www.backyardnature.net/n/14/141221ec.jpg.

A single leaf better showing its lower lobes appears at http://www.backyardnature.net/n/14/141221ed.jpg.

On the page showing last week's Burhead, a picture shows a leaf's unusual and pretty venation. This week's plant leaves display similar venation, but it's not as ordered and elegant as last week's. You can see veins of this week's plant at http://www.backyardnature.net/n/14/141221ef.jpg.

The flowers, however, look quite similar -- though their petals are more narrowed at their bases into short "claws"-- as you can see at http://www.backyardnature.net/n/14/141221eg.jpg.

Below the flowers, the three green sepals are curiously ribbed, as seen at http://www.backyardnature.net/n/14/141221eh.jpg.

This week's white-flowered aquatic has reason to share many features with last week's Burweed because it belongs to the same genus, Echinodorus. Last week we had Echinodorus subalatas; this week we have ECHINODORUS BERTEROI, also known as Burhead, since normally the name givers don't look at such details as we do.

This week's Echinodorus berteroi is found in clay soils of wet ditches, streams and shallow ponds from Wisconsin and South Dakota south through the central US, plus here and there elsewhere in the US, especially California, and south through Mexico and the Caribbean area, and then also in South America. It's a strange distribution and one wonders what history fragmented its range so, and places it so solidly in the south-central US, but absent or present only in spots elsewhere.

Last week's Burhead mostly bore fruits, and the few flowers seemed to represent more of an afterthought than a genuine flowering season. This week's Burhead species is just beginning to flower, its inflorescences mostly occupied with unopened flower buds, and there wasn't a fruiting head to be seen.

In some parts of its distribution, decoctions, or "teas," brewed from our Echinodorus berteroi have been used traditionally to treat epilepsy. A 2006 paper by Buznego & Pérez-Saad in the journal Epilepsy Behavior found that the decoctions significantly controlled aspects of induced epileptic episodes in rats.

*****

BEACH FOAM/ BIOFOAM
On flamingo-viewing tours, especially after the wind has blown a few days, some visitors seem as impressed with the spume, or foam, that builds up wherever the wind blows it, as with the flamingos. During my first visit here in 2006, one day I was with a tourist among the salt pans of Las Coloradas when we came upon spume blown in such quantity across the road that it came up to the car door's window as we passed through it. You can see that at http://www.backyardnature.net/n/06/061204x.jpg.

A moody picture taken this week of a more typical accumulation at the water's edge is at http://www.backyardnature.net/n/14/141221fm.jpg.

A handful of foam showing its soapsuds-like quality is at http://www.backyardnature.net/n/14/141221fg.jpg.

A shot showing how it blows inland littering the beach is at http://www.backyardnature.net/n/14/141221fn.jpg.

It even gathers up against Río Lagartos's storm wall and docking area, blowing over the wall with shreds of it, sometimes the size of basketballs or larger, rolling across the street like tumbleweed. It's shown around the boats at http://www.backyardnature.net/n/14/141221fq.jpg.

Where the foam forms a thick layer, often it composes itself into interesting designs, as shown at http://www.backyardnature.net/n/14/141221fp.jpg.

Besides its abundance, the most fascinating feature of this foam is its resiliency. You'd think that when its bubbles touch the dry pavement as shreds of it roll across a street, they'd burst, but the shreds stay intact until they blow up against a wall. Deposits linger a day or more. What makes the bubbles so tough?

There's a whole branch of science that looks into that question. The foam is known by such names as sea foam, ocean foam, beach foam, biofoam, and spume. You can download for free a 2010 paper reviewing the topic called "Biofoams and natural surfactants," and explaining things at the molecular and energetic levels, at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2954283/.

The short answer to what makes our beach foam so unusual is that it's caused by dissolved organic matter in water issuing from the mangroves, and also in open water resulting from decaying algae. The dissolved organic matter acts as a "surfactant," or foaming agent, that makes bubbles tough.

This science of foam doesn't restrict itself to beach foam. Particularly interesting foams includes that of which nests of various species of tropical and sub-tropical frogs are fashioned, and the hardening foams into which locusts and praying mantises lay their eggs. Some insect larvae, such as those of leafhoppers, froghoppers and spittle bugs, surround themselves with long-lasting foam as protection against predators. Horse lather is pretty interesting, too, made possible by a protein called latherin.

When you're out in the estuary on a windy day and a big shred of foam blows off the water's surface and sloshes into your face, and you wonder about it, your mind can just drift in all kinds of directions.

*****

SOLSTICE
In the Northern Hemisphere, today is the most majestic and meaningful day of the year. It is the Winter Solstice, when days stop growing shorter, and begin becoming longer. Spring begins now, though temperatures will lag a few weeks behind. Best wishes to all who see the beauty in this day, and who will, with me, watch in awe as the promise of the new natural cycle manifests itself.

*****

FEATURED ESSAYS FROM THE PAST:

"Trickster" from the June 12, 2011 Newsletter, at http://www.backyardnature.net/n/p/110612.htm

"Tweeting" from the October 2, 2011 Newsletter, at http://www.backyardnature.net/n/p/111002.htm

*****

Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.backyardnature.net/n/.