Bagging a little impersonator and other surprises

The shrew-mole, Neurotrichus gibbsii, with its flexible nose-probe in action.

"I'm goin' for shrews", I told my friend Terry who lives in California's Humbolt County.

The fog-bathed redwoods of California's north coast is the land of banana slugs, giant salamanders, red-tree voles, and shrew-moles, among other zoological wonders.

A Sonoma Shrew matches the color 
of redwood duff. 

My assertion that I was going to camera-trap shrews was a bluff.

I was hedging my bets.

I knew Terry's cat, "Muir" periodically catches shrews in the garden, and the cinnamon-colored shrew on the left is proof.


I also knew that kneading sunflower seeds into leaf litter and humus attracts shrews as well as mice and rats, and I submit the photos below as proof.

Sunflower seeds lured these Canadian and Alaskan shrews to my camera traps last summer.  

That afternoon we set camera traps (Sony s600s and Pentax Optio E60) in the redwoods, and the next morning found that the plan had paid off.

The pictures were short on resolution but good enough to identify two of the three "Soricomorphs", or "insectivores" as they were once called.

The Sonoma shrews were easy to identify by color and size.

A Sonoma shrew (Sorex sonomae) face-to-face with a baby millipede
(the pale elongate object in front of it).

The other shrews were either Wandering shrews (S. vagrans) or Trowbridge shrews (S. trowbridgii), which look identical unless you give them dental examinations.

My big thrill however was "bagging" a shrew-mole.

This is the world's smallest species of mole, but it's an excellent impersonator of shrews.

There's no question it's a mole; the quintessential mole-features are there in the teeth, skull, and the absence of external ears.

Its scaly tail with black bristles and constricted base is also decidedly un-shrewlike.

At some point in its evolutionary passage the ancestral shrew-mole struck out on an independent path.

It either lost or never acquired the other features of its family -- the over-sized "man-hands", the velvety pelt, and the predilection for subterranean foraging.

The transformation gave us a mole that can't "swim" the soil with the talpid breaststroke, doesn't makes mole-hills, and lacks the napless and velvety mole pelt that once adorned Yankee waistcoats.

Shrew-moles walk on the soles of their forefeet, which is impossible for moles to do, and sometimes they walk on their knuckles, like anteaters, armadillos, and gorillas.

What's more, they can stand bi-pedally like a squirrel and climb into low vegetation, which moles can't do.

And then there's the mole-snout.

Shrew-moles perfected it as a somewhat flattened and flexible walking stick with lateralized nostrils.

The foraging shrew-mole taps its nose center, right, and left with each step.

Dalquest and Orcutt, who studied the species nearly 80 years ago reported that the snout "may be thrown high in the air, twisted to one side or the other, rapped on the ground, or hooked under the body."

When it sniffs out a sowbug or earthworm, the shrew-mole thrusts its nose, and hooks and pulls out the prize like little Jack Horner.

The photo below seems to show it nose-plucking sunflower seeds the same way.

A shrew-mole roots for sun-flower seeds in redwood duff.

Most of the photos were false-triggers probably caused by something scurrying through the frame before the shutter fired.

I was hurriedly clicking through these "blank" images when the time-lapse effect revealed a Brownian swarm of pale larval millipedes.

These I assumed were instars of the yellow-spotted millipedes (Harpaphe haydeniana) so common in the area.

An immature miilipede or instar, presumably
the yellow-spotted millipede. 

In one frame a shrew rooted sunflower seeds in a flock of 12 baby millipedes.

In another frame two dozen baby millipedes grazed together peacefully.

It was like a miniature Serengeti with hunters and hunted drifting on and off the stage of life.

Wow, I had made a discovery!

"No wonder there are shrews here, there's an endless supply of tender nourishing millipedes."  

Or so I thought.

Yes, they looked like "easy pickins", but were they shrew fodder?

It was time to search the literature.

I found that Robert Stebbins, the late and great herpetologist once dropped a couple of millipedes (Tylobolus stebbinsi) into a jar containing a western skink, and despite the lizard's predatory restraint it was dead in 3 hours.  

Millipedes look meek, but their "repugnatorial glands" are highly effective weapons of chemical warfare.

Their many-segmented-bodies are equipped with stink glands, which can be selectively activated to release any number of noxious gases depending on the species.

The gas has a distracting effect on predators such as mice and birds, which immediately lose interest in their meal, blink their eyes, plow their faces in the soil, and go into fits of self grooming.

Yellow-spotted millipedes produce hydrogen cyanide which in low concentrations has a pleasant almondy-smell  (and gives me an appetite for Danish pastry).

According to Bug World the species is toxic to shrews.

Are immature stages also toxic, or as toxic as adults?

Millipede specialist Bill Shear informed me that baby millipedes can produce toxins as early as the 3rd instar.

At this stage of development they are probably too small to interest shrews or shrew-moles as food.

This probably explains why the myriad baby millipedes safely grazed while the shrews ate sunflower seeds nearby.

"When frightened, Neurotrichus makes an unbelievably swift, scuttling dash for cover."
(Dalquest and Orcutt, 1944, p. 391)

References:

Dalquest, W. AND D.R. Orcutt. 1942. The biology of the least shrew mole, Neurotrichus gibbsii minor.   American Midland Naturalist, 27:387-401.

Eisner, T. and J. Meinwald. 1966. Defensive Secretions of Arthropods. Science, 153, No. Shear, W. 3742:1341-1350

Shear, W. A. 2015. The chemical defenses of millipedes (diplopoda): Biochemistry, physiology and ecology. Biochemical Systematics and Ecology, 61:78-117.

Stebbins, R.C. 1944. Lizards killed by a millipede. American Midland Naturalist. 32 (3):777-778.


Acknowledgements:

Many thanks for Dave Rentz, Petra Sierwald, and Bob Mesibov for leading me to Bill Shear, who kindly shared with me his excellent and fascinating review of millipede chemical defenses.