While out in the garden this weekend I spotted a gulf fritillary, Agraulis vanillae incarnata. They’re stunning butterflies:
What first caught my eye was the silver reflections of the spots on the bottom of their wings. In direct sunlight it looks like they’re metallic; very eye-catching. But when the same butterfly is in diffuse light, those spots look white:
Compare the first and second picture, and you’ll see that in addition to changing from metallic to white, the butterfly can also choose how much color to show on its underside. When it spreads its wings (as in the first picture), the bright red/orange coloration of its forewing is revealed; but when it rests with both wings pulled together and upright (as in the second picture) it can completely hide the red/orange color, thus showing only brown and white/silver. It can also partially separate the wings, to reveal just a bit of color (as it liked to do when it was annoyed with how close I was getting).
And speaking of color, check out the top of those wings:
This butterfly only held open its wings for a few seconds after each flight attempt, so spotting the true colors of the wings takes finding one in flight and then watching it land.
For a fourth, and final, view of the gulf fritillary, how about a head-on look?
Sleek and slim, complete with a coyly resting forelimb.
And in case you didn’t realize, all four of these images are of the exact same individual. It’s surprising how different it looks depending on angle and lighting.
The larvae reportedly only eat passion flower vines; I wonder which of my neighbors has one.
Planarians are free-living aquatic flatworms that are staples of high school biology labs. The species I was able to photograph, Dugesia tigrina, is fairly small, growing up to about an inch in length when stretched out.
Planarians are utterly adorable. Their heads have cute little eyespots (ocelli) that sense light and auricles (the triangular extensions) that reportedly sense water currents. The eyespots lack lenses and a retina, so these cute little worms aren’t looking up at you and seeing your face, but they can detect the intensity and direction of light, allowing them to swim away from light (which is one of the easiest behaviors to observe in them; shine a light on them, and they’ll swim directly away from it). And when they move, they glide through the water with serpentine elegance.
The dark portions of the eye are not actually the photosensory nerves. Instead, the dark portions are pigment-filled cells that partially surround the photosensory neurons, shading them from one side (thus allowing them to detect the direction of light without a lens, retina, or movable eye).
While many flatworms are parasitic, these planarians are not; they’re free-living omnivores that swim around in freshwater ponds nomming on whatever they can find predators feeding on small insects and other invertebrates they’re able to capture (see comment thread for citations). In the lab we frequently feed them small pieces of liver or thymus.
The way flatworms feed is just awesome. Instead of having a mouth at their head, they extend a tube (their pharynx) from the middle of their body and latch this tube onto their food. They then “suck” the food up through this tube and into their digestive tract.
Speaking of guts, flatworms’ digestive tracts aren’t built like ours are: they have just a single opening that leads to and from their digestive track. This contrasts with our style of digestive tract, which has two openings: a mouth and an anus. The planarian style of digestive tract is called a gastrovascular cavity, and it can be seen in the following image of a preserved planarian slide:
And yes, this does mean that digested food has only one way out: through the same opening that they used to get the food in.
Planarians are used in biology labs primarily thanks to their easy availability from biological supply houses ability to regrow tissues from traumatic injuries: when cut in half they can regrow the other half of their bodies. This is because while they can reproduce sexually using sperm and eggs, they can also reproduce asexually via fragmentation. Fragmentation is a reproduction mechanism wherein an organism literally pulls itself in half, with both halves growing into complete new organisms. This leads to the classic high school biology “experiment” wherein students cut flatworms in half and wait for them to regrow. We won’t be doing that here. But this picture of two flatworms swimming next to each other almost looks like it 🙂
I get live planarians each semester to show my biology classes, but sadly most students just give them a passing glance. Next time you get a chance to observe these cuties, put them in a dish of water, get a dissecting microscope and some liver, and plan to spend some time with them. They’re great fun!
It’s fall here in coastal Orange County, CA1, but determining that it’s fall can be difficult since we don’t have trees filled with yellow and red leaves. Around here I find that there’s no better indicator of fall than seeing one of these hanging around outside2:
These orb weaver spiders come out every year in late summer and early fall, building webs at dusk that are frequently more than a foot across and can have individual lines of silk running more than 10 feet from attachment point to attachment point. They’re amazing animals, and I love to see them every year3.
This year a few took up residence close enough for me to try out my new macro lens. And, since it’s almost Halloween, it’s a perfect time to post up some spider pictures. Here’s one of the spiders just hangin’ out:
In this profile shot you can see how the spider has a small strand of silk attaching herself to the web as a safety-strap:
The attachment points of all eight legs onto the bottom of the cephalothorax is a fun feature to focus on (and probably the last view of many a doomed insect):