Tales from Tanzania: So, why do zebras have stripes, like, for real?

Today we saw dozens of very photogenic zebras. This got David and me talking: What came first, the zebra or the stripes?

baby Zebra

There are plenty of theories as to why the zebra has stripes – some more fantastical than others.

According to one African tale, the zebra was once pure white. One very hot day, the zebra went down to a watering hole to drink, but the watering hole was being guarded by a baboon bully who didn’t want to share. The zebra and the baboon got into a fight over the water and during the course of the fight, the zebra backed into the baboon’s fire and tripped. The hot branches left black scorch marks on the zebra’s hide.

While that tale, and others like it, are certainly fun to hear, they aren’t terribly scientific. So what says science?

One popular theory posited is that the stripes act as camouflage, but zebras graze in the open in relatively short grass. The stripes aren’t really making them blend into much of anything.

Another theory is that the stripes make it harder for a predator to pick out an individual from the group. Scientists originally believed that the stripes, when viewed at a distance, would simulate heat waves. Thus, that close-up would be confusing, because all the zebras would blend together. In reality, lions are the main predators of zebras and they generally hunt at night. A zebra’s stripes would, in fact, make them more distinct and visible in the moonlight.

The flip side of this theory says that the stripes help zebras recognize individuals in the larger group. This is actually supported by research, which shows that captive zebras prefer standing next to a patterned wall rather than a solid colored wall, but not 100 percent understood.

A relatively new theory that seems to have some merit is that the zebra’s stripes make excellent fly repellant. Cattle (and zebra too) are more susceptible to illness caused by the tsetse fly, which bite as a reaction to movement and dark colors. In fact, the tsetse fly prefers to bite through dark clothing even when a light, bare arm is available.

To test this theory, one study looked at horsefly bites on horses. They set up five “targets” for the horseflies — one black, one white, one grey, one with horizontal stripes and one with vertical stripes. The great target and the target with the vertical stripes had the least number of bites.

Why? The horsefly, like most insects with compound eyes (including the tsetse fly) has the ability to see polarized light. This improves their ability to see solid and dark colors, allows them to “see” heat signatures and enables them to track moving objects (especially dark ones). Because of these specially adapted eyes, the zebras’ stripes would make them disorienting to the horsefly. The stripes, hypothetically, break up the shape of the zebra and make it harder for the fly to focus in to bite.

While this all sounds great in theory, scientists haven’t conducted these same tests on actual zebras in Africa, but they are pretty positive the results would be the same.

Kwa heri ya kuonana!

Comet ISON Sprouts a Double Tail

Today’s guest post is written by John Moffitt, Astrophysicist & HMNS Volunteer.

Amateur astronomers are getting a better look at Comet ISON as it dives toward the sun for a Nov. 28th close encounter with solar fire. As the heat rises, the comet brightens, revealing new details every day. This photo, taken Nov. 10th by Michael Jäger of Jauerling Austria, shows a beautiful double tail. One tail is the ion tail. It is a thin streamer of ionized gas pushed away from the comet by solar wind. The filamentary ion tail points almost directly away from the sun.

Comet Ison gets a double tail - 111013 - crop

The other tail is the dust tail. Like Hansel and Gretel leaving bread crumbs to mark their way through the forest, ISON is leaving a trail of comet dust as it moves through the solar system. Compared to the lightweight molecules in the ion tail, grains of comet dust are heavier and harder for solar wind to push around. The dust tends to stay where it is dropped. The dust tail, therefore, traces the comet’s orbit and does not point directly away from the sun as the ion tail does.

Comet ISON is currently moving through the constellation Virgo low in the eastern sky before dawn. Shining like an 8th magnitude star, it is still too dim for naked eye viewing, but an increasingly easy target for backyard optics. Amateur astronomers, if you have a GOTO telescope, enter these coordinates.

Four comets visible in the pre-dawn eastern sky. Look with binoculars before the sun comes up.

4 comets skymap - 111213

Comet ISON Briefings at HMNS

November 29 – December 1

To find out whether Comet ISON survives its close encounter with the Sun and how to see it in December’s morning sky, come to the Burke Baker Planetarium Friday through Sunday of Thanksgiving weekend. An ISON update will precede each Planetarium show!
PLANETARIUM LECTURE
“Tracking Comet ISON and Other Possible IMPACTS”
Thursday, December 5, 6 p.m.
Tickets $18, Members $12
Comets and asteroids that roam the inner solar system and are a possible threat to Earth. Comet ISON will be grazing the Sun on November 28, and if it survives, it may come within our view. Dr. Sumners will give an update on Comet ISON and other incoming objects. Includes viewing of the show Impact!

Click here for tickets and more information on the Comet ISON briefings.

Tales from Tanzania: The banks of the Nile that divide two crocodiles

In a previous post, I mentioned that beetles are my favorite invertebrates — which sort of begs the question, “What’s your favorite vertebrate?” And that’s an easy one: Alligator mississippiensis or the American alligator. I am lucky that we live in Houston, close to alligators, and even luckier that we have a juvenile alligator in our live animal collection.

For now though, I am super excited to see a Nile crocodile. I have been assured that we will get a look at one today, as we travel through the Grumeti River area in the Western Corridor of the Serengeti National Park.

nile_crocodileUntil about two years ago the number of crocodilian species numbered 23. Was a new species discovered? The answer is kinda, but not really. Modern science proved what the ancient Egyptians already knew: The “Nile crocodile” is actually two species: the Eastern Nile crocodile (Crocodylus niloticus) and the Western Nile crocodile (Crocodylus suchus). The smaller, more docile Western Nile crocodile was commonly used in Egyptian culture (mummified, kept at temples, etc.) while evidence shows that Egyptians knew the larger, more aggressive Eastern Nile crocodile was to be avoided. DNA evidence comparing living crocodile populations and mummified crocodiles proved the distinct difference in the two species and brought the total number of crocodilians up to 24, of which nine are currently threatened or endangered.

What’s more, the same DNA study also showed that the Eastern Nile crocodile was more closely related to four species in the Caribbean than it was its neighbor, the Western Nile crocodile.

The Eastern Nile crocodile is the second largest extant reptile in the world. The largest accurately recorded male was shot in Tanzania and measured 21 feet, 3 inches and weighed approximately 2,400 pounds. In fact, we are visiting Tanzania at the perfect time to get a glimpse of these ambush predators as it is the dry season and they will be nesting.

I don’t want to get too close, however, as 63 percent of the 250 to 750 Nile crocodile attacks on humans per year prove fatal!

Bonus fact: A group of crocodiles is called a bask.

Tales from Tanzania: Hunting the “little” Big Five — with a camera lens

The safari, which literally means “journey” or “voyage,” began when Europeans traveled into Sub-Saharan Africa. They came to observe and record the flora and fauna of Africa, but the tales of the unusual animals brought other travelers — those in search of adventure and danger. Originally when one went on safari, one went to hunt the Big Five: lions, leopards, rhinos, elephants and Cape buffalo, ranked not by their size but by their difficulty to hunt on foot.

The modern iteration of the safari still has shooting, but now it is from behind the lens of a camera rather than down the barrel of a gun.

While Dave is excited to see and shoot the Big Five with his camera, I am more excited to see the “little” Big Five, as I am calling it. These are some of the biggest, baddest invertebrates on the African continent. Though they are (relatively) small, they can be fierce!

1. Siafu Ants (Genus Dorylus)

Siafu, also known as Driver or Army Ants, can live in colonies of up to 20 million individuals. When there is a food shortage, the ants will leave their hill and form marching columns of up to 50 million ants, traveling at about 70 feet an hour and destroying everything in their path. While they can be dangerous if an animal comes in contact with these traveling columns, they also perform an important service: pest control. The ants literally drive (hence the name) all other animals, pests and people alike, away from their homes.

Another weird fact: These ants have incredibly strong jaws. In fact, you can break off their bodies and leave the head without the ant releasing its hold, so they are often used as a natural emergency suture which will hold for days.

2. Giant African Millipede (Archispirosterptus gigas)

H_orig_millipede

Over 15 inches long and 2.5 inches around, the Giant African Millipede is one of the biggest and most recognizable invertebrates around. Despite its name, millipedes don’t really have a thousand feet. They actually have around 256 feet (four legs per body segment multiplied by 64 segments on average = invertebrate math). In general, millipedes can make excellent pets but many species come with a slightly unusual side effect: when irritated, they secrete a cyanide-based compound. To humans, the secretions are only mildly problematic, usually resulting in discoloration or mild irritation of the affected skin. However, these same secretions can burn the eyes or exoskeletons of ants and other predators. In the case of the Giant African Millipede, their secretions taste and smell really bad and so it makes them unappetizing to predators.

Another weird fact: Millipedes have a symbiotic relationship (try finding that as an option for your Facebook status) with tiny species-specific mites living on them. The mites keep the millipedes clean and tidy and the millipedes give the mites snacks and a place to live.

3. Ghost Mantis (Phyllocrania paradoxa)

ghost

All right. At 1.5 to 2 inches, these guys aren’t that big — but they are that awesome. Their superpower? Their camouflage. Ghost mantises are excellent little mimics. Living in dry areas on bushes and shrubs, the ghost mantis looks to all the world like a brown, dried leaf — even going so far as to rock back and forth slowly so they look more like a leaf blowing in the wind. As vicious little predators, their incredible camouflage helps them ambush unsuspecting prey with their spiked, raptorial forelegs.

Another weird fact: The closest living relatives to the mantid family are termites and cockroaches, both in the order Blattodea. All three had a common ancestor but developed independently.

4. Giant Walking Stick (Bactrododema episcopalis)

Just like the name suggests, this big bug looks to all the world to be a branch from the tree in which it hides. Stick insects are part of the Phasmid order, which comes from the Greek word “apparition.” They are aptly named as they can seem to appear from nowhere due to their ability to blend in. Although herbivorous, stick insects aren’t defenseless. Some species have spines on their legs, while others can spray irritating liquids at attackers. Yet others will regurgitate a nasty substance that will put a bad taste in a hungry predator’s mouth or reflex bleed, oozing a foul-smelling hemolymph from joints in their body. The giant walking sticks in Tanzania will average around a foot in length, but there is a species in Borneo that has been recorded at an incredible 22 inches.

Another weird fact: Some stick insect species can reproduce parthenogenetically (that’s a fancy word that means “without males”). A captive female stick insect can produce hundreds of all-female offspring without ever mating. In fact, there are some species of stick insects for which scientists have found no male specimens.

5. Goliath Beetle (Goliathus albosignatus, Goliathus orientalis)

goliathus_orientalis_preussi_1
I saved the best for last.

I love beetles and not only do they have cool beetles in Tanzania, they have two species of one of my favorite beetles: the Goliath. These big, bad beetles can grow up to 4.5 inches long and 3.5 ounces in weight — about the same size, weight and shape of a box of regular, powdered Jell-O. Incredibly strong for their size, these burly bugs can lift up to 850 times their own body weight. For the average 200 pound man, that’s the equivalent of lifting 77 tons!

jello

Boxes of Jell-O. In case you weren’t sure what those looked like.

Another weird fact: Beetles comprise the largest order of insects, Coleoptera, with 350,000 to 400,000 named species. This makes up 40 percent of all known insects and 30 percent of all known animals.

You know what’s even cooler? Scientists estimate that there could be 750,000 to 4,000,000 species of beetle that haven’t been named or discovered yet!

While I can’t be certain that I will get to see any of these critters in the wild on our trip, I am certainly hopeful that I will be able to return with photographic evidence of our encounters! Check back with Dave and I in early December and we will share some of our best photos from the trip.