Tag: invertebrates

Web of relationships

Today I was at Pescadero Marsh to look at live birds, but the dead things proved more interesting. It was just after low tide, and I saw two empty crab shells (prob. Red Crabs, Cancer productus), looking as though they had been eaten by gulls; interesting, but a pretty common sight, and it’s more interesting to actually see a gull eating a crab. Then I found the empty shells of two small crustaceans, organisms I’d never seen before. Here’s one of them:

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I have no idea what species this is, though I suspect it’s a fairly common organism.

Later, I walked along the dike near Butano Creek, and came across a dead mole (the notebook next to the mole is marked in inches):

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Given the size of those front feet and the short tail, I’d say it was a Broad-footed Mole (Scapanus latimanus). This is the third dead mole I’ve found in six months.

What interests me when i see dead things in the field is trying to figure out how they died, and how they are tied in to the ecosystem. The Red Crabs were easy to figure out — probably eaten by gulls. But why did that little crustacean die? it didn’t look as though another organism had tried to eat it, so was it simply left high and dry at low tide? As for the Broad-footed Mole, there was a definite hole in the other side of the animal, which could have been made by a bird’s bill; I saw Red-tailed Hawks and Northern Harriers hunting in the marsh; perhaps a raptor killed the mole, then got scared away before it could eat.

These are just possible scenarios; I’ll never know what really happened; but what I do know is that somehow these dead creatures reveal something about the web of relationships between organisms.

Invertebrate pitfall trap

When we humans think about the interdependent web of life, we tend to think about the relationships between ourselves and familiar organisms like mammals and trees. These are organisms that are either larger than us or relatively close to us in size, or they are taxonomically close to us. But if you conduct a survey of biodiversity in a given tract of land, the majority of non-microscopic species you find will be invertebrates, e.g., insects, spiders, crustaceans, etc. For a more realistic theological understanding of the web of life, I think it’s necessary to develop a more realistic understanding of biodiversity. It is easy and fun to feel a connection through the web of life to relatively cute organisms like rabbits, and to relatively majestic organisms like redwoods. Understanding our connections with organisms that are not particularly cute or majestic expands our idea of the interdependent web of life.

A few years ago, I participated in a blogger’s bioblitz; a bioblitz is a study that provides a “snapshot of biodiversity.” One of the tools used in a bioblitz is an insect pitfall trap; this kind of trap provides a sampling of insects and other invertebrates. I decided to place an insect pitfall trap in our front yard, so I could see some of the invertebrates that live in our urban setting.

Some online research revealed that pitfall traps made of glass are most effective (Oecologia 9. VI. 1975, Volume 19, Issue 4, pp 345-357), but the easiest way to make a pitfall trap is with nested plastic drinking cups. You dig a hole deep enough to bury the two nested cups, and pack dirt around them so that the rim of the upper cup is exactly at ground level. Then you can remove the upper cup, dump out all the dirt that fell into it when you were burying it, and then replace it. I used two nested 10-ounce clear plastic drink cups:

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To use pitfall traps ethically, you should check them at least once a day, and either release the captured organisms or collect them responsibly. If you’re expecting rain or hot sun, you should place some sort of cover over the trap, raised up an inch or two. The cover will keep rain and sun out, but still allow invertebrates to crawl into the trap. If you’re no longer going to use the trap, pull it out of the ground.

Here’s what I found in my pitfall trap this afternoon:

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The large organism appears to be in the genus Stenopelmatus; from looking at online identification guides, I’d guess this organism is probably a Dark Jerusalem Cricket (Stenopelmatus fuscus [Haldeman, 1852]). Where does it fit into the web of life? According to the Nevada at Reno Department of Extension: “Because it is nocturnal and comes out of the ground at night to roam around, owls, including the endangered spotted owl, feed on it. Probably other nighttime predators such as coyotes, foxes, and badgers eat it as well.” As for their food sources, the Orange County (Calif.) Vector Control District (OCVCD) says the primary food sources of Jerusalem Crickets are “plant roots and tubers; however, “they also feed on other insects, even their own kind.” The OCVCD also states that Jerusalem Crickets do not pose a health threat to humans.

The other organisms in the trap — you can see something like a centipede under the Jerusalem Cricket’s left antenna — were too small for me to have any hope of identifying. Besides, if I’m going to accurately identify insects and similar invertebrates, I’d need to ask an entomologist equipped with powerful binocular microscope.

More about insect pitfall traps.

Ants

Recently, I stumbled across the AntWeb site, sponsored by the California Academy of Sciences. Once you create a login (and all you have to provide is a username and password, no other info), you have access to tons of photographs of ant specimens, taken through a powerful microscope. Of particular interest to me is the online field guide to California ants, with photos of nearly all of the 270 resident species. The curator of the California pages writes:

“Prominent California ants include seed-harvesting species in the genera Messor, Pheidole and Pogonomyrmex; honeypot ants in the genus Myrmecocystus; a diverse array of species in the genera Camponotus (“carpenter ants”) and Formica; native fire ants (Solenopsis spp.); velvety tree ants (Liometopum spp.); and the introduced Argentine ant (Linepithema humile). This last named species is particularly common in urban and suburban parts of California, where it establishes dense populations and eliminates most native species of ants.”

I’ve always thoughts ants were interesting creatures. Now having looked through dozens of photos of ants I will go further and say that they are beautiful creatures. Even the Argentine ant appears beautiful, in spite of the destruction it does to native arthropods.

I am also fascinated by the written descriptions; these descriptions have their own kind of beauty, which may be found in their economy and laconic precision. Here, for example, is how to identify the Argentine ant — remembering that you will need a powerful binocular microscope to see all these details:

“Diagnosis among workers of introduced and commonly intercepted ants in the United States. Antenna 12-segmented. Antennal scape length less than 1.5x head length. Eyes medium to large (greater than 5 facets); do not break outline of head; placed distinctly below midline of face. Antennal sockets and posterior clypeal margin separated by a distance less than the minimum width of antennal scape. Anterior clypeal margin variously produced, but never with one median and two lateral rounded projections. Mandible lacking distinct basal angle. Profile of mesosomal dorsum with two distinct convexities. Dorsum of mesosoma lacking a deep and broad concavity; lacking erect hairs. Promesonotum separated from propodeum by metanotal groove. Propodeum with dorsal surface not distinctly shorter than posterior face; angular, with flat to weakly convex dorsal and posterior faces. Propodeum and petiolar node both lacking a pair of short teeth. Mesopleura and metapleural bulla covered with dense pubescence. Propodeal spiracle bordering posterior margin of propodeal profile. Waist 1-segmented. Petiole upright and not appearing flattened. Gaster armed with ventral slit. Erect hairs lacking from cephalic dorsum (above eye level), pronotum, and gastral tergites 1 and 2. Dull, not shining, and color uniformly light to dark brown. Measurements: head length (HL) 0.56–0.93 mm, head width (HW) 0.53–0.71 mm.”

Three predators

This afternoon, we went for a walk at Purissima Creek Redwoods Open Space Preserve in the Santa Cruz Mountains southwest of San Mateo. It was a stunning afternoon, warm but not too hot, with fog beginning to roll in up the canyons from the ocean.

As we hiked down into the preserve, we kept hearing a hawk screaming somewhere in the distance, but we never saw it. And then when we were hiking back up to the parking lot, there it was overhead: an accipter flying over the ridge we were on, then turning and riding the breeze coming up the canyon to our right. And what kind of accipter was it, a Cooper’s Hawk or a Sharp-shinned Hawk? I’d say it was perhaps a little larger, the neck a little longer, the tail a little more rounded, the wingbeats a little more deliberate: probably a Cooper’s Hawk, but I’m not good enough at field identification to be sure. It wheeled around, high above the canyon floor but at eye level for us; a couple of Band-tailed Pigeons came over the ridge, saw the accipter, and quickly ducked into the trees below us. Then the fog rolled up the canyon, and it was gone.

As we continued up the trail, Carol got about a hundred feet in front of me. Suddenly we both froze: walking the trail well up the hill in front of us was a dog-sized canid: a Gray Fox, its long tail behind it, its head turning from side to side, giving us a flash of the rufous fur up the side of the neck. It didn’t seem to notice us; it was busy watching the undergrowth on either side of the trail, and at least once it pounced at something.

We got back to the car a little after seven, and decided to go down to the beach to eat dinner. It was a beautiful foggy evening, and we walked along past Heerman’s and California Gulls, but the real attraction of the beach was the Velella velellas. When I was reading up on this species last night, I found a Web page by Dr. David Cowles that gave a possible reason why so many Velella velellas have washed up on northern California beaches:

“The angled sail makes it sail at 45 degrees from the prevailing wind. Some have a sail angled to the left, others to the right. Off California the right-angled form prevails, and these remain offshore in the prevailing northerly winds. Strong southerly or westerly winds, however, may bring huge aggregations ashore.”

We walked down the beach, making an unscientific survey: of the dozens of individuals we saw — ranging in size from less than two inches long to one that was as long as my notebook or approximately four inches (10 cm) long — all the sails had the same handedness (according to Dr. Cowles’ terminology, right-angled sails). Here’s a sketch from my notebook:

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I picked one up by its sail to look at the tentacles hanging down underneath. The velellas, like the fox and accipter, are predators, feeding on smaller organisms with their dangling tentacles. The tentacles seemed to descend from the central oval, and were of varying lengths. The sail itself felt smooth, flexible, and slightly rubbery; I dropped it back into the waves after I had looked at it.

Three very different predators — but each one a fabulously beautiful organism.

Velella velella

My cousin and her husband were visiting from Seattle, and she wanted to go to the beach to see the sun set in the Pacific. So Carol and I and the two of them drove over the Coastal Range to Half Moon Bay.

“Maybe we’ll see the velellas,” said Carol. The velellas — scientific name Velella velella — are small bright blue creatures that are distant relations of the jellyfishes. They float on the surface of the ocean, feeding underneath the water with tiny tentacles, and being blown about by the wind on their small sail. Recently, hundreds of them have been blown up along the shore in San Francisco and Santa Cruz and Humboldt County. But I was skeptical that we’d see velellas, since I had seen nothing about them being blown onto beaches in San Mateo County.

When we got to the beach, the fog was so thick it was obvious that we weren’t going to see the sun set in the Pacific. But Carol said, with a big grin, “Look, the velellas!” Sure enough, all over the beach just above the line of waves, were these little blue things. The biggest one I saw would fit easily in my hand.

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When you got down and looked at them closely, they were beautiful and amazing creatures. The San Francisco Chronicle interviewed Jim Watanabe, who works at the Hopkins Marine Station in Monterey County; the newspaper quotes him as saying, “They’re a nice reminder of the diversity of other life in the sea that we sometimes don’t think about.”

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The velella turns out to be a highly interesting organism that is not particularly well understood, as this Web page from Walla Walla University points out.

Great Meadows, Concord, Mass.

It was a perfect New England summer day — breezy, about 85 degrees, gentle blue sky — so Carol and I decided to take a walk at Great Meadows National Wildlife Refuge this afternoon.

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Above: Great Meadows National Wildlife Refuge, Concord, Mass., looking north over the lower impoundment

 

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Above: Northern Water Snake (Nerodia sipedon)
 

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Above: Common Milkweed (Asclepias syriaca), with unidentified pollinator