We’re often so mesmerized by the ant’s struggle that we forget she has an additional challenge. She has to navigate while walking backward. Ethologists at Paul Sabatier University wondered how ants do this so they baked some cookies and ran some tests.
Using a nest of Spanish desert ants (Cataglyphis velox) the scientists laid out large cookie pieces for the ants to find. Without disturbing the ants’ paths scientists noted how often they turned around to check their bearings. They also “airlifted” some ants away from the nest (no path to remember) and messed up the scenery for others so the path would look different.
To give you an idea how hard this is, imagine walking backward without the help of handheld Google/Apple maps. How often would you turn around to check where you were going? And what would you do if an enormous hand rearranged the scenery and nothing looked the same?
Some of the confused ants never made it, but those who knew their path walked 6 meters without peeking. This is equivalent to a human walking backward without peeking for the length of two football fields.
Perhaps it helps that ants can see nearly 360 degrees around their heads. Despite all the challenges they still get home.
Dovekies eat small invertebrates and fish but the majority of their diet is made up of copepods. A single dovekie eats 60,000 of them per day. Quadrillions(*) fall prey to dovekies during the breeding season. So … What the heck is a copepod?
Phytoplankton is really tiny, so small that you need an electron microscope to see it. The Barents Sea bloom above is thought to be Emiliana huxleyi, shown below. The disks are made of calcium carbonate which is also the primary component of seashells. The calcium in phytoplankton makes its way up the food chain.
Thus if phytoplankton is scarce, copepods are scarce and the dovekies starve. That’s how a seabird relies on algae.
(photos from Wikimedia Commons; click on the captions to see the originals)
(*) How many copepods? Here’s a back of the napkin calculation: Suppose there are 50 million dovekies, each one eating 60,000 copepods/day. Dovekies live in their breeding range for four to six months, so there have to be quadrillions of copepods available during that period. Dovekies aren’t the only animal that eats copepods. The numbers are staggering! (My original calculation had a power-of-10 problem. See Tom Brown’s correction.)
Insects that disappeared in the cold came out again during last week’s warm weather. On Wednesday I found a western conifer-seed bug on my front porch.
Formerly restricted to the western U.S., the western conifer-seed bug (Leptoglossus occidentalis, WCSB) has spread across North America, to Europe and South America. At 1/2 to 3/4 inches this “true bug” sucks the sap of developing pine cones and the pulp of pine seeds.
Travel is a tonic for seeing the world in new ways. This month my husband and I spent a week with his sister at Cape Cod where we had new weather, new scenery and new looks at plants I might have seen at home.
Our timing was pretty good. We missed the October 12 nor’easter but were on hand for the October 17 “bomb cyclone.” We didn’t lose power, but it was still very windy on the 18th when I visited Fort Hill, pictured above.
Birds were hard to find that day so I noticed plants such as this European spindle-tree (Euonymous europaeus) with puffy, pink, four-sided fruits.
The puffballs are actually a casing that holds orange fruit within. This ornamental has probably been planted in Pittsburgh, though I’ve never noticed it.
My favorite discovery was a hole in a leaf.
Who ate it? Perhaps this caterpillar did. I found him elsewhere on the plant.
And finally, the sun touched translucent red berries and made them glow at Bell’s Neck.
The small plants have a single leaf midway up the stem (lefthand photo) and were growing among pine needles. Please leave a comment to tell me what they are.
p.s. Thank you to Kerry Givens who identified the red berries as a Canada mayflower and the caterpillar as a Turbulent Phosphila moth.
(photos by Kate St. John except where noted in the captions; click the captions to see the originals)
So many woolly bear caterpillars have crossed my path this fall that, fearing they’d be trampled, I have carefully moved each one across the trail.
“Woolly bears” are the larva form of a common North American moth, the Isabella tiger moth (Pyrrharctia isabella). Since she is not dependent on only one host plant, Isabella is found in many habitats.
She even lives in the Arctic, surviving the winter because she has natural anti-freeze in her cells. Wikipedia describes how she does it:
The banded woolly bear larva emerges from the egg in the fall and overwinters in its caterpillar form when it literally freezes solid. First its heart stops beating, then its gut freezes, then its blood, followed by the rest of the body. It survives being frozen by producing a cryoprotectant in its tissues. In the spring it thaws.
The orange oakleaf butterfly (Kallima inachus), native to tropical Asia, is well named. The underside looks exactly like a leaf when the butterfly closes its wings, and it has wet and dry season forms that mimic the leaves of each season.
The butterfly stands out when its wings are open.
Watch it become a leaf as it flutters in place.
We have leaf-like butterflies in North America, too. Click to see the ventral and dorsal sides of the goatweed leafwing (Anaea andria). It ranges from southeastern Arizona to southern Ohio.
Though it’s nearly mid October I saw monarch butterflies migrating through Pittsburgh on Thursday and Friday October 10 & 11. Their timing seems late, but they were given a boost by August-like weather early this month.
While writing about the worldwide spread of Asian ladybeetles (Establishing a Bridgehead) I learned another amazing fact. These insects are cannibals when they need to be, but they’re careful about it. They avoid eating close relatives.
Asian ladybeetles (Harmonia axyridis) are insect carnivores, preferring aphids above all else. Their population surges when aphids are plentiful and goes hungry when aphids crash. Rather than starve, ladybeetle larvae eat eggs and smaller larvae of their own species. The strong ones survive, indirectly regulating their own population.
However, they also make sure that their own family survives …
Interestingly, H. axyridis recognize their kin and are less likely to cannibalize a sibling than a non-related individual (Michaud, 2003). If normal prey becomes scarce, larval mortality can be very high, with in excess of 95% of larvae failing to survive to adulthood, and in such circumstances cannibalism can be essential for survival.
Now that the weather has changed unwelcome insects will invade our homes including Asian ladybeetles (Harmonia axyridis) that resemble native ladybugs but don’t act like them. Also called “harlequin ladybirds,” they overwinter indoors, make a stink, and bite when frightened.
A hundred years ago we thought this bug was a great idea and repeatedly introduced it to the U.S. to control aphids. The introduced ladybeetles never made it in the wild until a population was found thriving near New Orleans in 1988. After that they spread like wildfire across the eastern U.S. and into Canada.
Thirteen years later they became established in South America and Europe(*). By 2004 they were in southern Africa. They hadn’t been introduced. How did they get there?
A 2010 study of their genetic markers revealed that those three continents were invaded by the eastern North America population. In a move called the bridgehead effect, Asian ladybeetles in the U.S. used our continent as a jumping off point to colonize Europe, South America and Africa.
Comb-footed spiders (Anelosimus studiosus) have a lot of personality. These social cobweb spiders live in colonies of 40-100 individuals, build their webs around branches, and hunt cooperatively to capture large prey.
The spiders exhibit either aggressive or docile personalities. If you know what to look for you can tell the difference. In the evening aggressive A.studiosus attack each other and then retire to opposite corners of the web; docile spiders rest side by side. Aggressive spiders come out to attack when their web is disturbed, the docile ones stay inside.
What happens to these spiders when they’re hit by a tropical storm or hurricane? Is there a difference in which spiders survive?
A 2018 study led by Jonathan Pruitt of U.C. Santa Barbara tracked 240 Anelosimus studiosus colonies in seven states including Florida, Alabama and the Carolinas. For baseline data they recorded the locations and personalities of the spider colonies. Later they searched for spider webs after a tropical storm or hurricane had passed.
You might think it’s futile to look for cobwebs after hurricanes, but individual spiders do survive, stay on their home territory, and rebuild. While humans are picking up the pieces, the spiders are too.
The study found that the storms always wiped out the docile spiders but the aggressive ones survived.
The relentless pressure of weather and nature is changing the spider population. Among comb-footed spiders, only the strong personalities survive.