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Marbled Salamander eggs

Marbled Salamander egg clutch under a log

Two friends from the Museum, Megan and Melissa, invited me to tag along with them yesterday, as did some fieldwork for a future workshop. Megan made a great find as she and Melissa were turning over logs at the edge of a vernal pool, looking for salamanders – some viable Marbled Salamander eggs. It seemed really late to us for this species to still have viable eggs (when we looked closely, they could see the well-developed embryo moving inside the eggs) so she grabbed a couple to photograph.

Marbled Salamanders have an unusual reproductive strategy compared to many other species in that the eggs are laid in the fall (usually October and November I think in this area). The female often scrapes out a little area near or at the edge of a vernal pool.  Vernal pools are fascinating and important habitats that may be dry much of the year and then fill with autumn and winter rains. The key is they have no fish, which makes them critical habitats for a number of species of amphibians, invertebrates and other animals. She then will stay with the eggs for some time (often a month or more) waiting for the water to rise so the eggs will hatch. If it remains dry for an extended length of time, she may abandon them and return to her underground burrows in the nearby woods until the next breeding season. Studies suggest that egg clutches where the female remains with them until they are covered by water have a higher offspring survival, perhaps because she helps protect them from predation or getting too dry. 

Marbled Salamander eggs

The 50 or 60 eggs Megan found were under a log at the edge of a large vernal pool. It was very moist but the standing water was still a few inches away from the eggs. Embryos develop to the hatching stage within a couple of weeks after being laid, but do not hatch until covered by rising water. So these eggs were very well developed. You can see the front legs and feet, the larval gills, some of the diagnostic lateral spots, and the eyes in the waiting “larvae”. My salamander reference (Salamanders of the United States and Canada by James W. Petranka) states, “when covered by water the embryos become oxygen stressed…this triggers the release (from hatching glands on the snout) of digestive enzymes that dissolve the egg capsule and allow the embryo to escape”. Amazing! 

A closer look

We put a couple of eggs in some water in a bug box so I could photograph them. Megan called Jeff Beane, a herpetologist at the Museum, and told him about the find. He said he did not recall seeing any viable eggs this late in the spring so he wanted to document the location. We walked down into the woods to show him, photographed the eggs and then walked back to the car. In those 40 minutes or so, the two eggs had hatched. The reference said it usually takes a few hours to a couple of days after flooding for the eggs to hatch. Guess these guys had waited long enough. The last picture is one of a larva from last year that I pulled from another pool. It was much older and larger than the ones from yesterday.

Large Marbled Salamander larva

Hollow log Bluebird house

This is in response to a friend’s request for information on a natural-looking bluebird house. I have made several of these out of appropriate sized hollow tree trunks (just compare to a commercial bird house for approximate dimensions). After finding and cutting the hollow log into reasonable lengths, I use a large screwdriver to scrape out the interior (if needed) so as to have a decent cavity. The entrance hole is made with a one-inch diameter drill bit. I usually rough up the edges a bit to enlarge it slightly and to make it look more natural. The top and bottom of the house are made with rough lumber and pre-drill attached with wood screws. I overlap the roof all the way around to provide some shelter from rain. 

The mounting bracket is made with a one-inch strip of aluminum (Lowes, etc. carry all of these pieces) cut to a length that allows it to be doubled over for inserting into the mounting pole. Drill two holes for the bracket to attach it to the back of the house. I am careful to use as short wood screws so there is not a sharp screw tip inside the nest cavity that might injure the birds. Then bend the bracket so the free end slides down into the mounting pole.  I usually compress the top of the mounting pole with a hammer so the bracket slides easily down into the narrow slit. One and a quarter-inch diameter electrical conduit is used for the long top mounting pole (I usually use 10 ft lengths and cut it in half) and it slides over a shorter, smaller diameter rod or piece of re-bar driven into the ground with a sledgehammer. Strike the conduit with a hammer a foot or so from the bottom to create a dent that will act as a stop when it hits the top of the ground pole as you slide the conduit down over it. The location of the dent allows you to adjust the height of the unit as needed.  The boxes tend to last a few years depending on the durability of the hollow log. I rarely clean out these boxes but they are used many times (after all, no one is cleaning out the natural cavities out there and some studies of nest boxes have hinted that parasites of nest parasites increase in number, thereby reducing nest parasite populations, if next boxes are not cleaned out frequently). Before setting in the box, I often finish the pole system off by slipping a length of 4 inch diameter PVC pipe over the mounting poles. Some say this may help deter snakes from climbing into the nest box. If I use it I always put sticks or grass or other debris down into the top of the PVC to prevent any birds from getting stuck in that pipe.

All of this effort is to provide a natural-looking cavity for the birds and a photographic backdrop for me. I usually put a pop-up blind near the nest box and allow the birds to get used to it empty before I start entering and taking pictures. Below are a couple of images from one such nest box in late afternoon light.

Crawling on your back...doing the Grub

June Beetle Grub

Found this huge grub in the topsoil pile the other day as I was adding soil to some garden beds. When disturbed, it curls itself into a C-shape as do many grubs. But this one then did something that only a very few grubs do - it started crawling away on its back. I first saw this behavior years ago on a teacher workshop with the museum...there were several large grubs at a pullout along the Blue Ridge Parkway that were crawling across the pavement surrounding a grassy area. A closer look revealed they were all crawling on their backs. A quick check in our field guides told us they were Green June Beetle larvae. Green June Beetles (Cotinus nitida) are large (up to 1 inch) beetles colored a beautiful velvety green, often with hints of bronze. I see them flying low over grassy areas and they are frequently encountered when I am picking ripe figs (another common name is Figeater beetle due to their fondness for these fruit). But today, it was the grub that had my attention.

Green June Beetle grub crawling on its back

Green June Beetle grubs are different from most grub species in the Southeast in that they come out of the ground at night and move from one place to another. They also crawl on their backs with their legs in the air. Grubs of some related beetles in the genus Euphoria, or Bumble Flower Beetles, also crawl on their backs, but they are generally less common. 

Green June Beetle larvae have stiff abdominal and thoracic bristles, short stubby legs, and wide bodies. When I left this grub alone for a few seconds it started crawling on its back by undulating and using its dorsal bristles and ridges to gain traction. I was impressed at how quickly it moved as it covered several inches in a few seconds. Seems like an odd locomotion strategy but all the references I looked at said the legs are too small to be useful for crawling (especially relative to other species of white grubs). 

Green June Beetle grubs overwinter as larvae and may become active on warm nights throughout the winter. Their burrows can be several inches deep (the depth depending on temperature and soil conditions). Their primary food is dead and decaying plant material. They resume feeding once the ground warms in the spring and then pupate in late May or early June. The adults begin emerging a few weeks later. I'll be on the lookout for the adults in a couple of months and try to learn more about their behavior.

Oh, I almost forgot to mention that I have a long history with grubs of various sorts. My most memorable encounter was in the Amazon years ago, while leading a teacher workshop with the NC Museum of Natural Sciences (where I worked for 24 years as an educator and naturalist). There were two Peruvian teachers with our group and one morning, while bird-watching, one of them got excited when he heard something in a log next to the trail. He ran back to the village and returned with a machete which he expertly used to chop out several very large grubs (as I recall they were well over 3 inches in length, compared to almost two inches for the Green June Beetle grub here). He had hard them chewing in the log and realized what a treat he had found. As any polite person would do, he offered the first bite of one to the three leaders of the group (turns out the grubs were considered delicacies by the locals). Well, being the youngest of the three, I naturally got the tail end of the grub as my share...let's just say I didn't chew much. Later that evening the remaining grubs were roasted and served as a great protein snack. I definitely recommend the roasted grubs (which were somewhat nutty in flavor) over the raw ones, both in taste and texture:)

Shed in the shed

Spider shed

Found a large spider shed in my shed this week. Believe it to be from a Dolomedes species (probably D. tenebrosus). This one would have been close to 3 inches across in total leg span! Their group is known as the Fishing Spiders, but this species is often found far from water, as in this case. They are not web-builders, but hunt large insects and other invertebrates by stalking and pouncing, much like a Wolf Spider (more on those in a future post). Spiders shed by pumping fluid upward which causes the cephalothorax to rupture and pop open like a lid. They then pull themselves out, leaving their old exoskeleton for shed owners to find and ponder.

Chilicerae on shed

 A close look at the chelicerae makes me appreciate the biting capacity of these large spiders. No wonder they can capture and subdue fairly large insects (I know there are some Wood Roaches and Camel Crickets in the shed). You can see the fangs at the tip of the chelicerae which are used to handle prey and inject venom. On either side of the chelicerae are the pedipalps, which look like short legs. They function as olfactory and sensory organs, and are used to manipulate food. In sexually mature male spiders, they are further modified at the tip to serve as a copulatory organ.