Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
Since it’s Darwin Day, I’ve featured only evolution-related issues, and let’s finish with some amazing pictures by photographer and entomologist Gil Wizen, taken from his eponymous website (with permission; note that he also has a Twitter page and a Facebook page). (N.b.: the photos are used with permission and cannot be reproduced further.)
In a post called “Petrophilia“, Wizen shows a moth in that genus, trapped in Belize, with some weird markings on its hindwings (captions are from Wizen):
Petrophila sp. in typical resting posture, partially exposing the hindwings.
Why are they there? We’re not sure, but one clue is how the moth rests:
Many moths rest with their hindwings concealed by the forewings, however these moths, belonging to genus Petrophila, had a unique body posture at rest, exposing only the dotted part of their hindwings. This pattern looked very familiar to me, but I could not pinpoint from where exactly. Then a few nights later one of these moths decided to rest pointing sideways with its head rather than upwards like most moths. And it finally hit me: this moth has an image of a jumping spider on its wings looking straight at you. The mimicry is so convincing that the moth wings even have hair-like scales where supposedly the spider’s head is.
Here’s the moth and its putative “model” (remember, this is a case of Batesian mimicry, in which a palatable mimic apes an unpleasant or dangerous model). Wizen is careful to hedge his explanation:
What I mean to say is that the color pattern on the wings of Petrophila species reminds me of a salticid spider, and perhaps it works the same for other animals as well. There is also a behavioral display that makes the mimicry even more deceiving: the moth moves its wings to mimic the movements of a jumping spider. In search for a second opinion, I turned to someone who breathes and sleeps jumping spiders. Thomas Shahan, who fortunately was around for BugShot, confirmed my suspicion and even came up with an ID for a possible model spider: a female Thiodina sp. And so we went on to find a jumping spider that looked like the one shown on the moths’ wings. In any case, to my untrained eyes it seems that this pattern is common in severalmothgenera, and in other insects as well.
You can see another moth with a similar pattern at his site, as well as a caddisfly with a salticid-like pattern.
Here’s the answer to “What’s that insect?“, via Twitter. Thanks to Matthew Cobb for sussing this out.
Yes, it’s a hemipteran (a “true bug”) in the genus Formiscurra (F. indicus), and it’s also a planthopper that’s an ant mimic. Notice the fake head in front of the real head!
Allow me to introduce you to #Formiscurra indicus, a species of piglet bug (Caliscelidae) known only from India!
See more here, including this photo of a hopper from the Catching Flies site. Caption: “This hopper is facing right, the forelegs are waved like feelers.”
Yes, folks, it’s a leaf-tailed gecko in the genus Uroplatus, and one cryptic mother! Members of this genus are some of the most remarkable mimics I’ve seen; Wikipedia describes their camouflage:
All Uroplatus species have highly cryptic colouration, which acts as camouflage, most being grayish-brown to black or greenish-brown with various markings resembling tree bark. There are two variations of this camouflage: leaf form, and bark form. The leaf form is present in only four described species, U. phantasticus, U. ebenaui, U. finiavana, and U. malama, which are also the smallest species. All other forms blend in well with tree bark upon which they rest during the day. Some of these tree bark forms have developed a flap of skin, running the length of the body, known as a “dermal flap”, which they lay against the tree during the day, scattering shadows, and making their outline practically invisible.
Here’s a bark form–really hard to see! Note the dermal flap (if you can see it):
And another. This species is a remarkable mimic:
And, just for fun, here’s the satanic leaf-tailed gecko, with the lovely name Uroplatus phantasticus, from Madagascar. It seems to occur in a variety of forms and colors, which makes me wonder whether it’s a single variable species or several species that are undescribed:
Here’s a video showing several species of the genus:
As the old saying goes, “Natural selection is cleverer than you are.”
Bees, in the order Hymenoptera, have four wings, like this:
What we see above on the cover of Bees of the World, an authoritative reference book, is a fly: a hoverfly—or “syrphid”—to be exact. Strawbridge’s post points this out, and explains why the authors might have made the error.
Hoverflies are in the order Diptera, which means “two wings”; and of course all flies, like the one on the cover, have two wings. I’m not sure how this slipped past the authors, but one reason is that these hoverflies are Batesian mimics: harmless flies that have evolved to resemble an insect (a bee in this case) avoided by predators. Many species of syrphids, as Matthew Cobb pointed out in an earlier post, mimic bees and wasps. Here’s a big group of syrphids that are Batesian mimics. The one on the upper left is especially convincing. And, as Matthew pointed out, syrphids can mimic the behavior of hymenoptera as well, further deluding potential predators.
When Brigit pointed out the embarrassing cover illustration in her post, she added this:
However, the internet is awash with wonderful, well researched, articles about bees that have been illustrated with photographs of hoverflies.
She goes on to explain Batesian mimicry, but since I’ve done that here several times before, I’m sure you all understand it.
h/t: Michael
UPDATE: There’s undoubtedly a name for the taxonomic version of the well known phenomenon of someone complaining about a typo or some other error, and including an error of their own. We – and Brigit Strawbridge – are guilty of exactly this error. For, as pointed out in the comments below and on Twitter by Morgan Jackson, the fly on the cover of the Bee book is *not* a hoverfly. It’s a muscid, and is NOT a mimic, as close inspection reveals. Nostra culpa. That having been said, many media outlets do indeed illustrate articles about bees and wasps with pictures of hoverflies. And while that is annoying to taxonomists (almost as annoying as mixing up a muscid and a syrphid), and can be used to tut-tut at the ignorance of photo editors and journalists, it also underlines the fact that these are often amazing mimics, which can fool a lot of the people, a lot of the time. – MC, p.p. PCC(E)
JAC: Instead of “Readers’ Wildlife” today, we’ll have a report on frogs by Greg Mayer, who’s just visited Costa Rica.
by Greg Mayer
Although quite cryptic on the forest floors it calls home, the smoky jungle frog (Leptodactylus pentadactylus) in the photo below is too obvious to be a candidate for “spot the frog”. This large species of frog (reaching over a 150 mm in snout-vent length) sports what in the military would be called “defense in depth”– a series of defensive behaviors and adaptations that help the frog avoid becoming someone else’s meal. The one in the photo below I encountered at the Lapa Rios Ecolodge, near the tip of the Osa peninsula, on my recent trip to Costa Rica.
Smoky Jungle Frog (Leptodactlyus pentadactylus), Lapa Rios Ecolodge, Osa, Costa Rica
It was a large individual (well over 100 mm), and we found it at night in the rainforest. Its first line of defense is that it’s quite hard to see against the variegated mixture of brownish leaves, twigs, and mud of the forest floor. (The red shine of the eye is more noticeable, but fortunately for the frog, natural predators don’t carry flashlights!) When first seen, the frog was sitting up at attention, but when we approached, it pushed itself down flat against the substrate, and as I moved around in front of it for a picture, it really pushed its face into the ground, making itself less noticeable.
Smoky Jungle Frog (Leptodactlyus pentadactylus), Lapa Rios Ecolodge, Osa, Costa Rica
Since all we wanted was pictures, the frog did not move to its further lines of defense. Had we provoked it, it would have assumed an elevated defense posture, with the back raised, also inflating its body and expelling air to make a hissing sound, similar to what is seen in some toads (Leptodactylus is not a true toad). I haven’t seen (or at least can’t recall seeing) this in Leptodactylus— the behavior was described in this species by Jaime Villa (1969)– but I have seen it in giant toads.
Elevated defensive posture of Leptodactylus pentadactylus (Villa, 1969: Fig. 6).
This of course draws a potential predator’s attention to the frog– having hidden, why would it now face up to its foe? This is where the next lines of defense come in. First, the frog is big, and this behavior makes it look even bigger. For some predators, the frog is a mouthful too far. Next, if the frog is touched, it exudes a copious and toxic mucus. This mucus induces a strong allergic response in humans, and presumably others, at least mammals if not all other vertebrates- intense sneezing, watery and itching eyes– the unpleasantness of which I can attest to from personal experience. It is said that people merely in the vicinity, who have not touched the frog, can, through aerial transmission of toxin droplets, get the same symptoms. The mucus can irritate the skin, and cause pain to any scratches or open wounds (which I fortunately did not have when catching the frogs). And the frog will also emit a loud, piercing shriek, which might well startle a predator into releasing its grip. Norm Scott reported that caimans were attracted to this cry, and even speculated that that was its function– to attract caimans to dispatch the frog’s predator– sort of like a bugle call to the cavalry!
More straight forward than the multi-layered defenses of the smoky jungle frog is the defense of poison dart frogs– aposematic, or bright, warning coloration, accompanied by very toxic skin secretions. We encountered two species at Lapa Rios. Phyllobates vittatus, with bright orange stripes, is a member of the genus which contains the three species of the poison dart frog family, Dendrobatidae, that are actually used by Indians to make poison darts.
Poison Dart Frog (Phyllobates vittatus), Lapa Rios Ecolodge, Osa, Costa Rica
We found three of them, during the day, along the Rio Carbonero. We also found three Dendrobates auratus along the paths at the Lodge itself, wandering about during the day, bold as brass, as is their wont. I’ve seen them quite abundant in other parts of Costa Rica, but we saw only three during 4.5 days at Lapa Rios. For neither species of dart frog was I able to get a very good picture; there’s a better picture of auratus in an earlier post, and, in another earlier post, more details and references on poison dart frogs. BBC Earth has a nice explainer on poison dart frogs, with links to interesting papers
Poison Dart Frog (Dendrobates auratus), Lapa Rios Ecolodge, Osa, Costa Rica
Savage, J.M. 2002. The Amphibians and Reptiles of Costa Rica: A Herpetofauna between Two Continents, between Two Seas. University of Chicago Press, Chicago
Scott, N.J. 1983. in D.H. Janzen, ed. Costa Rican Natural History. University of Chicago Press, Chicago
Villa, J. 1969. Comportamiento defensivo de la “Rana Ternero”, Leptodactylus pentadactylus. Revista de Biología Tropical 15:323-329. pdf
Reader Lou Jost, who lives and works in Ecuador, found a really cool beetle, and a case of possible mimicry that I didn’t know about. His descriptions are indented:
Here’s another weird insect I found. This one is a translucent chrysomelid beetle larva, subfamily Cassidinae, which builds a rough likeness of another insect or spider, by carefully placing bricks of poop onto its back with its “anal turret” (that’s a real term!!). It does this by touch since it can’t see what it’s doing back there. When this creature grows up it turns into a partly-transparent beetle that also has a fake insect on its back, a fly, but this time it is just done with pigment.
JAC: The adult, with spider-like markings on its back:
The adult also has amazing feet. They are like wet mops and can stick to glass and other surfaces, and withstand enormous forces (60-100 times their own weight). The liquid is a viscous lipid. The feet are marvelous under a microscope. I think the claws might be used as levers to get the wet, flattened, divided hairs to unstick from the surface.
I must have taken many thousands of images of this thing during its life. The foot pictures shown here required about 700 pictures each. You can see the microscopic droplets of lipids on the flattened hair tips. There are more photos and info here.
Last year reader Rodger Atkin sent an uncamouflaged photo of the lovely Oleander Hawk-Moth (Daphnis nerii; see it here). This year it’s on vegetation, and somewhat harder to spot. Can you find it? (Enlarge photo for help.)
