July 20, 2018
THORNBUSH DASHER DRAGONFLIES
The central Yucatan isn't a good place to see a variety of dragonflies because in our limestone-based karst topography there's little standing water, except in sinkhole bottoms and artificial ponds. The rancho's little concrete-lined pond is one of the latter, and one of the three dragonfly species I've seen there is shown on a Tridax procumbens flower head bent over the water at the pond's edge, at https://www.backyardnature.net/n/18/180720df.jpg
That's the Thornbush Dasher, MICRATHYRIA HAGENII, distributed from the southern US not far from the Mexican border south through Mexico to Panama. The OdonataCentral.org webpage for the species describes it as the most widespread tropical dasher extending into the US, and describes its habitat as heavily vegetated ponds and lakes.
Our little cement pond has no plants in it other than a perpetual algal bloom, though the arid scrub around it is somewhat thick in places, with plenty of thorny bushes. Thornbush Dashers are often recognizable because they raise their white-spotted abdomens almost vertically over their brilliant, iridescent eyes.
This species' common name, Thornbush Dasher, actually is a generic name for about 48 species belonging to the genus Micrathyria. The name serves its purpose in the US where other thornbush dashers are unknown or little known, but down here it's inadequate, though no other English name seems to be available..
This week the pond's Thornbush Dashers have been mating, as shown at https://www.backyardnature.net/n/18/180720dg.jpg
I read that females release their eggs, or "oviposit,"as they hover low over water, extruding egg masses about 2mm (1/16th inch) in diameter, flicking their abdomens upwards to release them. They also oviposit on available floating vegetation.
During summers the Thornbush Dasher wanders northward into the US sometimes as far as Arkansas. As global warming takes place it's a species that could turn up where it's never been sighted before.
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BENT-SKIPPER ON MY WASHRAG
At https://www.backyardnature.net/mexnat/bentskip.htm we look at the skipper-type butterfly known as the Widespread Bent-Skipper, and point out that an unusual feature of the species is it's bent-down wingtips. That page only provides an overhead view of the butterfly in which it isn't clear just how bent-down the wings are. This week a Widespread Bent-Skipper turned up on the hut's porch sipping moisture from the green washrag I'd just sponged the sweat from my body with. First, a top view of the visitor -- who enjoyed the washrag's mineral-rich moisture so thoroughly that he allowed me to get very close -- at https://www.backyardnature.net/n/18/180720bw.jpg
Now a view from the front, showing those bent-down wingtips, as well as the strawlike proboscis sucking up the good stuff, at https://www.backyardnature.net/n/18/180720bx.jpg
I'm still curious about why various bent-skipper species develop bent wings. Earlier I mostly saw them basking in sunlight on coolish days, and I thought that maybe the bent wings kept warmth beneath their bodies, but now we're in a season where keeping warm is no problem and that idea loses its appeal.
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CABBAGE BUTTERFLY CATERPILLARS
I've mentioned how here in the Yucatan, during the six months or so of the relatively cool dry season, I've never enjoyed such a fine crop of mustard greens. Up north, my mustard green beds normally are soon ravaged by insects. I've suggested that my success with mustard greens here is that the Mustard Family, the Brassicaceae, is a Temperate Zone family; members of the family are absent here in the Yucatan, except as occasional invasive weeds or planted, and sometimes people do plant cabbage here.
I've been eating mustard greens until now, well into the rainy season, but this week I pulled up all my plants. That's because suddenly the plants became heavily infested with caterpillars of PIERIS BRASSICAE, a butterfly commonly known as the Cabbage Butterfly, Cabbage White, and Large White. Cabbage Butterflies are commonly encountered throughout Europe, northern Africa and Asia to the Himalayas, as it's spreading fast to other parts of the world. Its current Wikipedia page mentions only scattered reports of a dubious nature of its appearance in the US, but that it's definitely established in South Africa and New Zealand. It's not supposed to be here in the Yucatan, but it's reported by amateurs like me on the Internet. My own evidence of the Cabbage Butterfly's presence here is shown at https://www.backyardnature.net/n/18/180720ca.jpg
The caterpillars cluster side-by-side on the underside of a mustard-green leaf exactly as they're known to do. As they grow, Cabbage Butterfly caterpillars undergo four molts and five instars. The ones in the picture seem to be third or fourth instars. You can see examples of two different instars at https://www.backyardnature.net/n/18/180720cb.jpg
In that picture the semitransparent, tubular items with black spots are "skins" shed as the caterpillars grew, passing from one instar to another.
Caterpillars of the Cabbage Butterfly feed on species of the Mustard Family, and I'm impressed that a female Cabbage Butterfly -- which I've never seen in the Yucatan -- managed to find a member of the Mustard Family in this isolated place. Mustard Family species contain "mustard-oil glucosides," which cause the caterpillars to taste bad to predators. It's supposed that this bad taste is why Cabbage Butterfly caterpillars are so brightly colored, instead of camouflaged: their showiness is a warning to predators. Often dangerous or bad-tasting organisms are brightly colored, and it's said that such colorful, unpalatable species are "aposematic."
The Cabbage Butterfly itself emits an unpleasant smell that deters predators, the odor deriving from the toxic mustard oil glycosides from food plants stored in the individuals' bodies.
So, this an interesting sighting. However, I'd rather do without the Cabbage Butterfly caterpillars in my wonderful mustard greens, than keep seeing the larvae eating my greens as I did this week.
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THE BAHAMA MIMOSA'S CURIOUS LEGUMES
During my recent camping trip to southwestern Campeche state, on the morning of July 2nd I emerged from the woods near the entrance to Chicanná ruins and began hiking eastward on the main highway between Chetumal and Escárcega. Soon it became apparent that vegetation in that area consisted mostly of species we also have in the northern Yucatan, just that the mix is different.
For example, around Ek Balam in the north the Wild Tamarind, Leucaena leucocephala, for long distances often forms nearly pure stands along roadsides. In southern Campeche, Wild Tamarind also was common along roads, but it's seldom much dominant over other species. Weedy roadsides were more diversified, probably because of the greater rainfall than up north.
A weedy shrub or small tree sharing the roadsides with Wild Tamarind was the Bahama Mimosa, often called Catsin by the Maya. Our Bahama Mimosa page is at https://www.backyardnature.net/yucatan/mimosa-b.htm
On that page you can see that Bahama Mimosa, a member of the Bean Family, bears twice-pinnately compound leaves, like those of acacias, produces spherical heads of tiny flowers, also like acacias, and that its legume-type fruits are unusual. They're flattish, with papery, jagged "wings" along their margins. Near Chicanná ruins I saw the species' mature fruits doing something interesting, shown at https://www.backyardnature.net/n/18/180720mm.jpg
Notice that instead of whole legumes falling from the tree, individual legume sections, called joints, come loose and fall away. Typically legumes split lengthwise, releasing bean-type seeds, but here the legume splits from side to side, and the seeds fall away still encased in squarish sections of legume husk. I've always assumed that the legumes' wings caught in the wind, helping the wind blow the legumes off the tree, but now I'm supposing that the wings cause the legumes to shake the squarish segments loose from their pods, to be blown away individually.
Because Bahama Mimosa is so weedy, I've always assumed that it enjoyed a wide distribution, but now I see that it's limited to the Bahamas and the Yucatan Peninsula, including Belize and lowland northern Guatemala.
One wonders why Bahama Mimosa doesn't also occur in the sizable landmass of Cuba, which lies exactly between the Bahamas and the Yucatan Peninsula. Some have suggested that ocean currents could have transported the seeds, but Grether and Camargo-Ricalde in their 1993 work "Mimosa bahamensis (Leguminosae) en la Península de Yucatán, México," (Boletín de la Sociedad Botánica de México 53) found that the tree's mature legumes as well as individual joints sink in water after 24 to 72 hours.
Hurricanes probably wouldn't have blown fruits and joints that far, and if they did, it's hard to see how they could have avoided sowing seeds in Cuba, where soil conditions are good for them. We're left with the idea that humans may have introduced the species from the Yucatan into the Bahamas, either intentionally or not. It's known that the prehispanic Maya traveled long distances in their canoes. But, if the Maya took seeds to the Bahamas, why not Cuba?
It's just one of those mysteries we may never solve.
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THE MANILA PALM'S MALE & FEMALE FLOWERS
At https://www.backyardnature.net/yucatan/manila-p.htm we look at the attractive and very much-planted Manila Palm. This week one of the ranch's Manila Palms was flowering, attracting a nice variety of small pollinators. Manila Palms are "monoecious," meaning that individual trees bear unisexual flowers of both sexes. You can see a marble-size male, or "staminate," flower bristling with cream-colored, pollen-producing stamens at https://www.backyardnature.net/n/18/180720vt.jpg
The male flowers of most palm species produce only six stamens, so bearing so many is a little unusual. In the blossom's center you can barely make out a spherical item exactly where the female ovary should be. That's a vestigial ovary, destined to never produce a fruit despite being surrounded by so many vigorous male parts. Another Manila Palm standing just a few feet away was loaded with very different-looking female flowers, two of which are shown at https://www.backyardnature.net/n/18/180720vu.jpg
The three fresh-looking, curved stigma arms at the flowers' tops indicate that the ovaries are receptive, ready to receive pollen from a male tree. Notice the stigma arms' rough or maybe short-hairy upper surfaces, which help airborne pollen grains stick there when they land. Also, notice at the ovary's base the six broad, rounded scales representing the flower's three sepals and three petals. When the ovary matures into a fruit these scales will form a conspicuous, pale, tough, cuplike item known as a "cupule," and will look somewhat like an acorn's cup subtending the nut, which in the Manila Palm's case is bright red, so the cupule is very noticeable.
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OLD MAN OF THE MILPA
A milpa is a traditional indigenous American cornfield in which bean vines and ground-running squash are interplanted with corn, the bean plants returning nitrogen to the soil, and the squash's big leaves shadowing the soil, helping it retain moisture. Milpas, are planted in forest plots opened up by slash-and-burn clearing and are productive for three to five years or so, until weeds, insects and diseases move in. Then the plots are abandoned, the forest grows back, and eventually is slashed and burned again.
Mayan milpas are only a fraction as productive as North American cornfields using chemical fertilizers, pesticides and hybrid, often gene-manipulated seeds. However, milpa farming has sustained the Maya for thousands of years and, at least at low population densities, has proved to be sustainable.
Still, nowadays few milpas in this area produce their potential output because mostly they're planted in order to receive a government subsidy. Milpa farming is hard work, chancy, and people like to eat other things than home-cooked corn products, beans and squash. Young Maya are somewhat embarrassed to be seen working in a milpa. In this area, at the end of each milpa growing season, most milpas are so neglected that they're choked with weeds, and large numbers of raccoon-like coatis, and birds such as Yucatan Jays, take much, most or all of the produce.
However, on the road between the rancho and the village of Ek Balam there's a milpa planted he old way, with interplanted corn, beans and squash. Last month an old man could be seen there poking holes in the ground with his stick, taking seeds from his sidepouch, dropping them into his holes, and covering them with his foot. Nowadays his crop is coming up. You can see a section of his field at https://www.backyardnature.net/n/18/180720mp.jpg
A view across his field is at https://www.backyardnature.net/n/18/180720mq.jpg
The old man's textbook traditional milpa is so unusual that when I bike by his field and he's out there working, I wonder what he's thinking and feeling. What causes him to spend mornings in his milpa when other men in the village are doing other things, or producing milpas only in name, for the subsidy payment?
I like to think that he's out there because he's obstinate, just won't give in to the new changes, and doesn't care what his neighbors think. I like to think he's figured out that the way the world and humanity are going is all wrong, that he doesn't want any part of it, and that he's decided that if he's going to do anything at all, he can't do better than plant seeds in the ground, whether or not his family will eat his corn, beans and squash.
The old man's situation is worth thinking about because all the rest of us also are facing profound social, political and economic changes coming on fast. Right now civilization is at a threshold at which robots and computer algorithms are poised to begin doing nearly all the work of humans, and doing it cheaper and better. What's to happen to us when nobody want to pay for our work, and we don't even have milpas for growing food?
Maybe the old man in his milpa offers us at least part of a strategy for dealing with these times, even if we're unable to produce a milpa. Here are the strategy's main points:
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Best wishes to all Newsletter readers,
Jim
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