Reader Bruce Lyon sent some nice photos of wild spider monkeys (Ateles) from Costa Rica, as well as some information (his comments are indented):

During my recent trip to Costa Rica we spent time at a functioning farm/ecotourist lodge) that has lovely cabins set along a river. This farm is crawling with both spider and howler monkeys and is the best place I have yet come across for spider monkeys because they are so abundant and so tame. Spider monkeys are not always tame and will show their displeasure at humans on the ground under them by throwing things like fruit or branches and then quickly fleeing. The monkeys at this farm (called Cañas Castilla in the event that any readers are looking for fun places to visit) have the run of the place, and are even allowed to harvest as many oranges as they want from the orange groves.

I’m not sure which species these are, but I know a reader will enlighten me.

An orange thief—in both meanings of the phrase.

The monkeys are social and we often see fairly large groups moving through the trees. The name spider monkey is wonderfully apt given their long hairy limbs. The long arms are useful for the monkeys’ primary mode of travel—using their arms to swing from branch to branch (“brachiating”). It is amazing how quickly they can cover ground.  In addition to brachiating, they also make spectacular leaps to cross gaps between trees (I estimate some leaps to cover 10 feet).

Not an action photo of an animal brachiating, but simply a monkey resting in a silly pose, but the photo does give a sense of the reach their long arms give them:

Spider monkeys also have prehensile tails and they can hang from the tail alone, which they do while dangling to get fruit. I photographed this monkey, nicely showing off its prehensile tail wrapped around a branch, from the front porch of our cabin:

Below: A baby riding on its mom. Really small babies are carried much of the time but older babies often move through the trees themselves and only get help from mom when needed. Mom helps these older youngsters in two ways.  For leaping across big gaps, the baby climbs aboard, holds on tight and mom does the leap for both of them. For smaller gaps a mother sometimes makes a bridge that the baby can crosse — the mom’s tail grabs a branch on one side of the gap while her hands hang on to something on the other side of the gap, and the kid then scoots across. This past trip I saw this happen twice; in both cases the kids looked like they were going to try to make a leap but then chickened out. The moms, who had been ahead, then came back and formed a bridge for the kid to cross. These are good moms!

Check out the tail on this mom: it is naked on the underside, presumably for better grip for wrapping around branches.

I watched a large troop moving through the trees along the river and it soon became clear that every animal was using the exact same cross point to leap between two trees. This gave me lots of chances to photograph animals in mid leap since I could predict where they would cross. The light was pretty bad but the photos still show what the leaps are like.

Below is a mother and baby about to leap. I love the expression on the baby: excited or freaked out?

A couple of photos of fully airborne monkeys:

You don’t like worms? That’s a narrow-minded attitude—especially in light of these beautiful marine worms, photographed by Alexander Semenov, posted on Colossal, and called to my attention by several readers (how do you people find these things?).

I’ve chosen a few for your delectation, but go look at them all. I have no idea what the species are (they’re all polychaetes, a class of segmented worms [“annelids”]) but perhaps some readers know. Some of these have fantastic morphological complexity.

The site’s description follows, and be sure to look at Semenov’s photos of jellyfish and starfish.

Our favorite photographer of everything creepy and crawly under the sea, Alexander Semenov, recently released a number of incredible new photographs of worms, several of which may be completely unknown to science. Half of the photos were taken at the Lizard Island Research Station near the Great Barrier Reef in Australia during a 2-week conference on marine worms called polychaetes. Semenov photographed 222 different worm species which are now in the process of being studied and documented by scientists.

The other half of the photos were taken during Semenov’s normal course of work at theWhite Sea Biological Station in northern Russia where he’s head of the scientific divers team. We’ve previously featured the intrepid photographer’s work with jellyfish (part 2, part 3), and starfish.