Sunday, January 18, 2015

Camouflage and Hiding in plain sight

Most insects are small and delicious. So their constant problem is how not to be eaten. In our SW Facebook group we already explored aposematic colors in this context. This week it's the opposite strategy: Hiding from predators. We won't be purists. I will include insects that pretend to be parts of plants or other natural structures, even if those are sticking out like thorns. Some people may want to call that mimicry, but I will include them here. 

Platycentrus acuticornis Montezuma Wells, Yavapai County, Arizona, USA
May 30, 2010...

Enchenopa sp. (undescribed)
Florida Canyon, Pima County, Arizona, USA
November 19, 2010
If a bug 'pretends to be' a thorn among thorns, is that mimicry or camouflage? Anyway, a number of Membracidae (Treehoppers) avoids predation that way.

Santa Rita Lichen Grasshopper, Leuronotina ritensis, Ruby Rd, AZ
This is Bob Behrstock's photo that he allowed me to use for the d_UAIC on flickr, so I guess this use here is fair.
Anyway, all observations I know of are from AZ, so I'd be curious to see any from other areas - Sonora Mexico probably has them, too....
The grasshoppers seem to be confined to rocks with those specific encrusting lichens, so I assume they also feed on them,
By the way, the hind wings are bright orange

Sphingicampa montana (Syssphinx)

By themselves, and illuminated by flash at night the caterpillars of our small silk moths, the Sphingicampa (Syssphinx) species, seem outrageously colorful and showy. the little slivers on the back are actually reflective like mirrors, reminding of sparkling Turkish dancing dresses.
All of them live in leguminous trees or bushes with leaves broken down into little leaflets, like mimosa and mesquite. I had no good daytime photo (I borrowed this one from Ken Cave)... I usually don't see the caterpillars during the day because they are so well camouflaged. All the white markings and even more so the reflective bits break down the shape of the big caterpillar among those tiny leaflets, even seen against the light. You will find white or silver markings on almost all insects that live among Mesquite leaves, Creosote leaves, and Tamarix and Juniper twigs. There are stink bugs, geometrid caterpillars, leaf hoppers, katydids, grasshoppers - I'd even count the silver striped Glorious Scarab here (it feeds on juniper)

Synchlora frondaria, a green geometrid
on Acacia,  Molino Basin, Pima Co, AZ June,
 David L. Wagner says, "A Mardi Gras caterpillar that is out of costume only after a molt. The larva fashions its disguise by attaching plant bits (usually flower petals which it has chewed free of its food plant) to its back.

Mecaphesa (?) sp. and Misumenoides formosipes (middle and right) from AZ desert and sky islands
Many ambush predators have evolved to be masters of camouflage. This one is especially impressive:
"Crab Spiders in the genus Misumenoides formosipes are a sit-and-wait predators that do not use a web for prey capture. Instead, they sit perched atop flowers with their front pairs of legs spread open wide in preparation for capturing whatever unlucky insect comes near. These spiders are actually capable of actively changing their body color from yellow to white, or vice versa, depending on the flower they are perched on. They do this by transferring a liquid, pigmented material to the cuticle. The color change is not instantaneous; it can take anywhere from three to nine days to complete (G. N. Dodson, personal communication, June 2014)." Adapted from
Hamataliwa grisea, a Lynx Spider. Molino Basin, Pima County
Good camouflage requires more than just the right colors or textures. Behavior is a big factor, too. First of all, the bug has to stay on the surface it is adapted to. Then it has to sit still. But there remains the problem of the cast shadow, as illustrated in the toad bugs that had more important things in mind. This spider gets it right, though. The legs are pulled towards the body to form one inconspicuous, continuous shape. Bristles form a soft connection without overhangs or abrupt angles to the surface it is sitting on. The result: No sharp cast shadow.
Hamataliwa grisea, a Lynx Spider. Molino Basin, Pima County

Tetragnatha (Longjawed Orbweaver) Santa Cruz River bank,Marana
Pima Co AZ,
The problem with macro photographs for this topic is that we usually blow the bug's cover when we have finally found him. Imagine this Tetragnatha (Longjawed Orbweaver) in a tangle of twigs and grasses : she'd be quite hard to spot.
These spiders are often close to water where they spin circular (orb) webs, mostly in the horizontal plane, often just inches above the surface of water where they can intercept emerging insects like midges, mayflies, and stoneflies.

Arizona Unicorn Mantis Nymph (Pseudovates Arizonae)
Molino Basin, Catalina Mts, Pima Co, AZ
This girl was already big, over 2 inches, when I found her and molted twice before becoming a green-winged adult. The nymph seems more cryptic than the adult, but I must admit that I personally have found several nymphs (I raised this one) an no grown-up ever. The nymph has all the right patterns, colors and the shape to blend in with dry branches. It also moves in slow motion and hides its directed movement towards prey by simultaneously swaying from side to side as if the whole motion was wind induced. I'd call that camouflage of intent..

Gratiana pallidula (Eggplant Tortoise beetle)
Many Leaf Beetles (chrysomelidae) are toxic and announce that fact with warning colors, but a good number survives by being cryptic - larva to adult. Tortoise beetles have successfully eliminated the cast-shadow problem. The seamless contour with the surface is combined in some species with extreme strength holding the beetle to that surface - nearly impossible for ants to grasp or dislodge.
Gratiana pallidula (Eggplant Tortoise beetle)
can be found on several solanaceae

Gerstaeckeria sp. on Cholla, Blue Sky Rd, Willcox, Cochise Co. AZ

Cactus weevils in the genus Gerstaeckeria are hiding by lining up with the tufts of glochids in the areoles of a cholla cactus. The weevils are night active and come out at dusk when they blend in with those structures of the cactus surface even better. Experienced entomologists like Charlie O'Brien are not fooled. They look for tell-tale little circular feeding marks rather than for the weevils themselves. So right now, Charlie is describing a new species of the genus that lives exclusively in one of the rare and protected pineapple cacti. Obviously, the bugs are oblivious of the endangered species laws. On the other hand, that weevil is probably more endangered than its host.

Gelastocoris oculatus, Big-Eyed Toad Bugs.
 These pea-sized True Bugs live along muddy freshwater shorelines and are often overlooked. Their locomotion is described as walking, sometimes hopping. When we had 'hopping' as a weekly theme, I could not find any Heteroptera that hop - well, here is one. If that makes them look (if you see them at all) even more like baby toads, I don't think that would be a great mimicry protection, because those, too, get eaten. I think toad bugs and baby toads are both profiting from being nearly invisible. But: Motion draws attention. Occasional hops are of shorter duration than continued crawling along and thus would betray them less - so hopping may be a behavioral aspect of their camouflage.

Schinia miniama Kitt Peak, AZ, March
Some day active noctuids spend their time on spring time asteraceae. They feed, mate and lay their eggs on the flower disks and the caterpillars develop eating the maturing fruits. Some species are colored like the multi colored Indian Blanket and they usually even sit in the right position to fir the pattern. Maybe someone has a photo of that

Chrysoecia thoracica, Lochiel, Cochise County, AZ
 In September I saw a number of 'flowers' that I did not recognize. Then I realized that the 'petals' were actually sleeping noctuid moths. They were all oriented with their wings sticking out, heads towards the center.There were groups of them around many of the flowers (Cosmos parviflorus) When I got very close to photograph this group, 3 got upset and flew away, but you can still see the deception that all five together would have produced.

These were my contributions to this weeks topic of the Facebook Group SW U.S. Insects & Arachnids. While many aspects of camouflage and hiding in plain sight were covered, many more could have been mentioned, or were posted by other members. Robyn Waayers had a particularly nice Bag Worm cocoon.
Amy Jaecker-Jones posted trichoptera larvae masquerading as leaf litter at the bottom of a creek

1 comment:

  1. Impressive post Margarethe. I really enjoy the level of detail you provide on these guys.