A couple of weeks ago I made a short visit to our lowest-elevation reserve, the Rio Anzu Reserve (1100-1200m elevation) in the Amazon basin, to mark some special orchids for a visiting student to study. Lowland Amazonia is the richest habitat on earth for birds and trees, and also hosts a seemingly never-ending parade of crazy insects. A trip to this reserve is always a mind-boggling experience, even though the reserve is very small and lacks larger birds and diurnal mammals due to indigenous hunting pressure in the surrounding area. (However, black jaguars stalk this forest unseen by human eyes, but recorded in several different camera traps…)
Quite often at the trail entrance of this reserve there will be a big mixed flock of mostly-insectivorous birds scouring the branches and leaves of the forest. On this trip I met with the flock as soon as I got out of the taxi-truck that brought me there. The flock and I seemed to follow the same forest path for a long way, and I enjoyed their noisy company. A particularly sharp bird call alerted me to the “leader” of the flock, a Fulvous Shrike-tanager (Lanio fulvus) an uncommon bird which does not occur at our higher elevation reserves. This is one of the famous “liar” birds (not to be confused with Lyre-birds!) that watches for hawks, etc, and warns mixed flocks of danger, but will sometimes “freeze” the flock with a false alarm call when it sees a bird flush a particularly appetizing insect. It then grabs the insect for itself (Munn 1986). In spite of its occasional duplicity, the presence of this species allows the other flock members to find more food, since they don’t have to waste as much time looking around for danger (they rely on the Shrike-tanager to do that). So a flock will generally cluster around the local pair of Shrike-Tanagers, and they move together through the forest.
Throughout the day fancy butterflies filled the air. My favorite (at least on this day) are the Heliconius butterflies. These butterflies have larva that feed on poisonous passionflower (Passiflora sp.) leaves, and they themselves thus become poisonous to birds. The adults have strong warning colors and patterns, which show a very complex but interesting geographical variation. In any given area, often two different Heliconius species will share exactly the same pattern, but in a different region, the same two species can share a completely different pattern. The geographical variants are intensely studied to give clues about the process of incipient speciation, the possible locations of wet “refugia” during past hot dry epochs, etc. I saw many species that day, but only managed to photograph one.
Appropriately I soon found a giant passionflower plant nearby. This species is a canopy liana but has specialized short clambering flowering stems that often come out near the ground. They are pollinated by hummingbirds.
The crown of white pointy “tentacles” in the center of the flower have an important function. Flowers that attract hummingbirds generally produce a lot of nectar, and this nectar is a tempting resource for other creatures, including many that play no role in pollination. Flowers with better defenses against nectar robbery will leave more descendants than those that don’t, so very elaborate defenses have evolved in many hummingbird flowers, including this one. The white spikes protect the nectar below them. They are easily parted by a hummingbird’s needle-like beak, but a clumsy ant or bee can’t get its head close to the nectar.
The back of the flower also has a defense against nectar robbers. The bracts surrounding the base of the flower have “extrafloral nectaries”, glands that produce a bit of nectar themselves. Ants and wasps like to hang out there and drink this nectar, and these nasty bugs scare away other kinds of bugs that could chew through the back to get to the big store of nectar inside.
The day was full of grasshoppers. I photographed an especially flashy one, but many more escaped my lens. One of the grasshoppers I did manage to photograph was carrying two parasitic mites (ticks) on one leg. Mites are commonly seen on insects in the tropics, but I don’t know much about them.
Along with the grasshoppers were many katydids. Most North American katydids eat leaves, but in the tropics things are more complicated. I found a nasty carnivorous katydid munching the severed torso of a walking stick [male of the genus Oreophoetes, according to Yannick Bellanger’s Comment below], while
the walking stick’s mate another walking stick [possibly a new species according to Yannick Bellanger’s Comment below] sat and watched, motionless. The juices of the half-eaten walking stick, in turn, attracted tiny gnats which gathered under the katydid’s head waiting for a chance to steal a mouthful. It was a miniature Serengeti. The annoyed katydid repeatedly swatted the gnats with its forelegs, just like I was swatting the slightly larger gnats that were bugging me. [Edited Dec 1 to reflect my growing doubts that these two walking sticks really belong to the same species. They seem too different from each other. Any experts out there with an informed opinion? Edit June 22 2016: Thanks Yannick Bellanger for the IDs and for answering this question in the Comments. Both are males, of different genera.]
After a couple of hours I reached the Rio Anzu itself, an easy 15-minute walk if I had ignored the interesting bugs. This is where the ladyslipper orchid Phragmipedium pearcei grows on the wet riverside limestone. The plants are often submerged when the river rises. On this day the river was low and there were many individuals in flower.
At first glance the texture of this ladyslipper orchid flower is unremarkable. It looks smooth like any other flower. I had never given it a second look until that day. A microscope revealed that the flower was a complex mosaic of textures, hairs, glands and stuff I still don’t understand. The hairs were clearly guides for the insect pollinators, which must first land on the white flat rim of the orchid’s pouch or “slipper” (the pouch is called the “lip” in orchid terminology). This white rim has a row of random green spots, and another loosely organized row of larger brown spots. When magnified, the green spots turn out to be many long parallel dark green ridges, separated by greenish brown “valleys”. The effect is almost iridescent. Edit Dec 1: In response to Lisa’s question below, I did some research and found that the pollinator is a female fly that thinks these green spots are actually aphids, the prey of the fly larvae. The female lands on the flower to lay eggs among the “aphids”, and falls into the pouch. My speculations about the spots looking like fly eyes were wrong.
Eventually the pollinator must fall into the pouch (perhaps drugged by the orchid). Once the pollinator enters the pouch, it finds itself trapped, with limited ways out. Most of the inner surface of the lip is only lightly hairy, but one strip is carpeted with long hairs, and this strip leads the insect up to an escape route that passes directly under the stigma and anthers. The insect thus is forced to pollinate the flower if it wants to get out of there.
The variety of textures on this flower make me eager to look more closely at other flowers. Expect to see many more micro-photos here in the future!
Munn, C. A. 1986. Birds that ‘cry wolf.’ Nature 319: 143-145.