invertebrates – Page 24 – Seabrooke Leckie

Today at Kingsford – Wooly Bear Caterpillar

Yesterday I decided to take Raven on her daily walk in a different direction down the road for a change of pace. Our destination, instead of the abandoned property to the north, was a semi-private road to the south, that leads back through the woods to a row of mostly cottages. There aren’t any “Private Road” signs at the foot of the road, so I’m not actually sure of its status – I won’t go anywhere if there are signs posted, as there are on some such roads, but I also haven’t encountered anyone down there to ask. The road seems to see a bit of traffic even during the winter, but very little, I mostly just know this by tire tracks in the soft road surface. I feel comfortable allowing Raven to bound about off-leash there without risk of encountering cars, and it gives us another place to go when we want a change of scenery.

The day was warmer than it has been in a while, but still only a degree or two above freezing, so I was surprised to discover this Wooly Bear caterpillar crossing the road. Very slowly. I was amazed that he was moving at all, really, given how cold it was, sunshine notwithstanding. I picked him up off the road and placed him in a warm patch of sun at the base of a broad, deeply creviced tree. Hopefully he was able to climb into a nook before dark, though he surely wouldn’t have had time to make himself a cocoon.

Wooly Bears (sometimes known as Banded Wooly Bears) are the caterpillar form of the Isabella Moth (Pyrrharctia isabella). The photo above is an adult I caught at my blacklight back in June. Isabella Moths have two broods each year, one that mates in the spring and lays eggs that mature and pupate over the summer, and then these adults produce a second fall brood that overwinters as a pupa and emerges in the spring. They’ve got a wide range of foodstuffs, including birch, maple and elm, as well as various grasses, asters, clover, and others. This should make it relatively easy to raise one indoors, providing fresh food each day.

Folk lore suggests that you can tell how severe and/or long the coming winter will be by the amount of black on each end of the caterpillar’s body. Although this is largely bunk, there may be a sliver of truth to it, at least when the caterpillar is being examined close to the onset of cold weather. The red portion of the caterpillar continues to grow as it feeds and matures. Wet weather tends to stunt the development of this portion, making the black bands longer. The early onset of cold or wet weather, and therefore a longer winter, would result in a shorter red portion and longer black segments.

Unlike some fuzzy caterpillars, the hairs of Wooly Bears won’t irritate skin, so they’re safe to handle unless you have particularly sensitive skin. Of course, when you pick one up, most often it will curl into a ball for protection, “playing dead”, as it were. I was delighted to discover there are whole festivals devoted to this common caterpillar, such as the Woolybear Festival in Vermilion, Ohio, in the fall, a pre-winter equivalent to the spring tradition of Groundhog Day. According to Wikipedia, the Vermilion parade “in 2006 involved over 20 marching bands, 2,000 marchers, hundreds of animals, and over 100,000 spectators.”

Bird seed surprise

One of my responsibilities while house-sitting for my parents is keeping the bird feeders well-stocked. With the period of extremely cold temperatures (at least for this time of year – we’d be laughing come February) the feeders were a hive of activity, and the seed levels dropped steadily. The sunflower and thistle seed feeders were filled again without trouble, but when I dug the scoop into the bag of mixed seed, I noticed a sharp, distinctly mouldy smell. Peering closer, it looked like perhaps the peanuts had started to turn, and it was maybe spreading to the other seed, but I couldn’t really tell. It didn’t look really bad yet, so I stood there for a moment or two, holding the container in my hand, staring at the seed inside as I pondered whether it was still okay to put out for the birds (mould can be poisonous to birds once it’s progressed).

I finally decided better to be safe and not put the seed out, but while I was standing there contemplatively staring at the seeds, I noticed something else. Some movement. The seeds were starting to wiggle. And then…

…from between them, out crawled a tiny beetle. And then another. And a third. And before I knew it, the top was crawling with a dozen or more little beetles. More accurately, little weevils, as I could clearly see the thin snouts protruding from the front of their heads. Weevils are sometimes also known as snout beetles because of this feature. There are some 60,000 species in the weevil superfamily, Curculionoidea. Most belong to the family Curculionidae, and about 2600 species from this family are found in North America. Most are herbivorous, and many are crop pests.

Probably the interaction most people will have with weevils is the opening of a bag of something to discover an infestation of them. They are common outdoor bugs, but are generally small and inconspicuous unless they happen to land on your drink glass or some other coincidental meeting. However, they do occasionally make it home in bags of grain or seed products. There are three species, all in the genus Sitophilus, who are encountered this way, but they tend to be so similar in appearance that identification to species is best left to an expert with a microscope. They have food preferences, but there is a lot of overlap and they will opportunistically infest other sources when their preferred food isn’t readily available.

The three species are Rice Weevil (Sitophilus oryzae), Granary Weevil (S. granarius), and Maize Weevil (S. zeamais), and their common names reflect their preferred food (here in North America, maize is more often called corn). They often come home in infested bags of bird seed (Granary and Maize weevils may prefer mixed seed, Rice Weevils are often found in sunflower), but will sometimes be found in packages of rice, beans, peanuts, or whole-grain cereals. I couldn’t tell which seeds specifically had been targeted in the package, although the amount of mould growing on the peanuts made me suspicious of them. I think that the decay of the seeds that the weevils had been feeding on, whichever ones they were, had lead to the mould.

The life cycle of these weevils takes about a month to complete, and requires temperatures of a minimum of 17 oC (62 oF), but ideally 27 oC (80 oF) and above, and moderate to high humidity. The adult weevil lays their eggs on appropriate seed or grains which will become the food source for the developing larva. When the egg hatches, the larva tunnels into the grain and sets up shop inside. It takes about 3 days for an egg to hatch from laying, and then the larva may be in the grain for another 18 days, at which point it develops into a pupa. Once the adult emerges from the pupa, some 6 days later, it stays in the relative protection of the grain until its exoskeleton has completely hardened and matured, about 3-4 days.

Because they spend most of their cycle inside the grain itself, it may be possible to be harbouring these little bugs in a stored product for a few weeks without even knowing they’re there. Generally speaking, the incidence of infestation is rare, and probably even if they are present the product is consumed before the eggs get a chance to develop and we’re never the wiser (consider it added protein). By the time the bugs reach adult, stage, however, consuming them or the secretions they produce can sometimes result in E. coli infections, depending on the weevil’s particular diet.

I dumped a few out on a blank piece of white paper to try to get some uncluttered photos of individuals, but I had minimal luck. They were just too quick! I found that initially they would curl up their legs and play dead, for instance if I shook the paper to knock them all back to a central starting point. But moments later they’d unfold and start hustling across the paper. Interestingly, their direction of movement wasn’t random. They all moved with a purpose, and while their particular direction varied, it was always directly towards the edge of the paper. I thought perhaps they were trying to get away from the bright halogen that was hanging over the center of the paper to provide illumination for the photos.

None of them ever tried to fly, which I think perhaps rules out Rice Weevil, which is supposed to be winged and attracted to lights. The Granary Weevil has poorly developed wings and can’t fly, and is also not attracted to lights. On the other hand, Rice Weevils are reddish-brown and have 4 pale marks on their wing covers (Maize Weevils are similar), while Granary Weevils are reddish-brown to black and unmarked. Going by that, it looks like I have both in this group. So who knows! When I submitted the images to BugGuide.net, the person who identified them thought it safest just to leave them at genus.

Today at Kingsford – Ichneumonid wasp

Raven was a bundle of energy today, so I ended up breaking from work a bit earlier than usual to take her out for a walk and hopefully tire her out enough that she’d sleep through the afternoon and let me get a few hours of solid worktime in. I took her out to the woods so she could run around off-leash for a bit, which burns more energy than simply walking on a leash along the road. Upon reaching the woods I sat her down to unclip the leash (an exercise in patience and discipline more than a requirement for getting the leash off), and noticed, on the ground between her front paws, this wasp. I steered her around it to prevent her from accidentally crushing it, and then while she scamped off to roll in the leaves a short distance away, I squatted down and ran off a few shots.

It’s a parasitic wasp of the family Ichneumonidae (drop the “ae” from the end to give the common name, ichneumonid wasps), subfamily Ichneumoninae. This subfamily is the second-largest of the ichneumonids, and among the most diverse. These wasps are parasites of caterpillars, laying their egg inside the host’s body, where the wasp larva develops and then emerges as an adult (inevitably killing the caterpillar, of course). Females are identifiable from males by the pale bands on their antennae (males lack these, or have indistinct bands), and are often found crawling on foliage or among the leaf litter looking for caterpillars, which may explain the situation with this individual, although it seems late in the season for her to be searching out a host. In fact, the 6 C (43 F) temperatures are not really favourable to most insects, so it was a little surprising to encounter her at all. Kaufman’s Guide to Insects notes that the females of some species hibernate as adults in protected spots such as under loose bark on logs or stumps. I don’t know what species she is (ichneumonids are difficult to identify to species simply from photos), and Kaufman doesn’t specify anyway, but perhaps she was searching out a hibernation spot.

If a tree falls in the forest

Forests are generally known specifically for their living trees. The tall pillars, their stout trunks reaching for the sky, the branching canopies casting shade on the ground below – they are the very definition of forest, and without them the forest would not exist. And yet, the living trees are only a small part of what forms a forest. Just as vital are the dead trees, the ones still standing as snags and, perhaps more importantly, the ones that have fallen as logs.

Logs play a vital role in the forest ecosystem. As they begin to break down and decompose, they return nutrients back to the soil that may have been locked up in that tree for decades, or even hundreds of years. Because they’re essentially nutrient-rich piles of fertilizer, they provide excellent spots for new life to grow. Often in the tropics, where the majority of the nutrients in the ecosystem are contained within the living matter, fallen trees are swarmed by young plantlings looking for a good start in life. It’s not unusual to have trouble seeing the log for all the little trees and plants growing on it. Such is not usually the case in the temperate north here, but they do still foster growth, often moss or fungus, sometimes ferns or grasses, occasionally young trees.

Rolling a log over can reveal many secrets. They are home to many critters, from vertebrates like salamanders or frogs that hide underneath, to insects and invertebrates that tunnel below or inside. These latter groups are an important part of the decomposition process, breaking it down into pieces that are easier for bacteria and little organisms to digest. The longer a log has been down, the further along the decomposition process as all the little critters get to work. A newly-fallen log is still strong enough to support a person’s weight, but do the same with one that’s been on the ground a number of years and your foot will go right through it. The amount of time it takes for a log to break down completely varies according to the size, density and composition of the wood and the local conditions. Dry and cold conditions tend to slow the decomposition process, as the organisms responsible for much of the cycle are less active, and denser wood will take longer to rot (even within the same tree, sometimes, different densities between the sapwood and the heartwood can create hollow logs, or logs where just the centre remains). A giant red cedar, which has a dense, oily wood, may take a century to completely return to the soil.

I wrote about carpenter ants before, but there are many species of invertebrates that also call dead trees and logs home, and which woodpeckers find tasty. Fallen logs are riddled with woodpecker holes just as often as standing snags are, and it’s not unusual to flush a Pileated or other woodpecker up from what seems like the forest floor. Woodpeckers, and Pileateds specifically, probably help in breaking logs down as they chip pieces off during their excavations. Woodpeckers aren’t the only birds to use logs, though. Ruffed Grouse males will sit atop a large log to perform their drumming displays, where they beat their wings rapidly to create a deep staccato beat, using the log to amplify the sound’s acoustics. Many species of ground-nesting birds will build their nests under the overhang of a fallen log.

Forests go through different stages of maturity, and one of the characteristics of a mature forest is the presence of many fallen logs. A truly mature forest, however, not only has fallen logs, but also has fully decomposed logs. Because the latter no longer look like logs, they can be hard to spot. In walking the woods around here I spent some time searching for a fully-decomposed log to take a photo of, but the forest is too young. I suspect much of the land around here was cleared for farming at one time or another, as there is evidence of split-rail fences that apparently run through the middle of the forest. It could be that the forest in this area is only about 60 or 70 years old. Certainly the really thick, tall, craggy trees that characterize a very old forest are few and far between.

I found a couple that might possibly have been an old log or stump but couldn’t say for sure. The above was one (it’s quite difficult to get a photograph that adequately conveys the sense of a bump in the land, it turns out). These old, decomposed logs show up on the forest floor as raised hummocks. Often they’re long and narrow, much like the log they used to resemble. They can be mistaken for burial mounds, as they have the same sort of formation. Oftentimes you can see two or three trees growing in a line along the hummock, evidence of seedlings that got their start on the decomposing log, now long gone. Because of the amount of time necessary to return a grown tree back to the forest floor, these hummocks are often used as a sign of forest maturity.

Logs are good for having fun, too. Children use them as balance beams. Small ones can be used to create forts. Hollow ones can be crawled through as tunnels, or lived in like treehouses. And I know one puppy who had a blast vaulting over them like agility jumps.

Hidden in the wood

The other day, as Dan was chopping wood for our wood-burning fireplace, our main source of heat for the house (there are baseboard heaters, too, but those are expensive and less efficient to run), he sliced the above log neatly in two to discover it wasn’t empty. The log cracked squarely down the centre, revealing a long channel down the middle with a secondary tunnel coming off one side, connected to a small chamber. And in this chamber were a bunch of carpenter ants. Unfortunately, I wasn’t home when he discovered the ants, and they were gone by the time I returned, but he kindly set the log aside for me knowing that I’d want photos. You can’t tell from the photo, but the surfaces of the tunnels were worn smooth from thousands of tiny little feet.

The logs Dan was chopping were ones that had been sitting in a stack on the property for perhaps a couple years, trees that had been cut down when the landlord thinned the forest to improve the view of the lake. Despite that the house is heated by wood stove, for whatever reason he’d never gotten around to cutting and hauling the logs back to the house. Free wood is free wood, however, and Dan, being the industrious person he is, set about turning it into half a cord of firewood. I rarely find other organisms in my firewood, and when I do it’s usually either fungus, or the engravings of wood-boring beetle larvae underneath the bark. It’s hard to say if the carpenter ants made their home in this log while the tree was still standing and just never moved out, or moved in after it was cut down.

While walking the woods today I discovered a tall, dead snag, riddled with holes. The large holes, some bigger than the palm of my hand, were the work of a Pileated Woodpecker. Pileateds drill trees looking for insects that hide inside. Wood-boring beetle grubs are good, but they’re especially fond of carpenter ant colonies, perhaps because once they discover a colony there’s a bonanza of food inside. They drill rectangular holes into the trunk, characteristic in shape and size. Dan watched one woodpecker in our front yard as it started a new hole by drilling in a straight, horizontal line to pierce the bark, and then vertically at either end of the horizontal line. Then it wedged its bill under the slab of bark, and pried it off. This technique of opening up a trunk for excavation explains why they usually have rectangular holes.

Carpenter ants live inside the trunks of dead trees (or house frames), where they excavate expansive galleries in the wood (you can see the tunnels and entry holes to other parts of the gallery in the photos here). Contrary to popular belief, they don’t actually eat the wood, but simply chew tunnels into it. The sawdust produced from “digging” the tunnels can usually be found at the bottom of the cavity, or at the foot of the tree. This network of tunnels and chambers forms their home, where the colony lives in a similar fashion to a wasp’s nest or bee’s hive. The size of the network can vary with the size of the colony; some colonies can contain as many as 10,000 or more workers. Carpenter ants prefer to build their nests in moist or damp wood, as it’s easier to chew apart. The wood in homes that runs the greatest risk of invasion are the old pillars or other exterior pieces that are exposed to the elements or some other regular source of water, and therefore prone to rotting.

Carpenter ants are generally omnivorous scavengers, feeding on dead insects and many other plant and animal sources of food (although, unlike termites, they are unable to handle cellulose, a structural compound in plant material). A few species will sometimes “tend” aphids, collecting the honeydew that the aphid produces and offering protection to the aphid in exchange. Interestingly, the ants don’t get all the amino acids they need from their diet alone, and so in their gut all carpenter ants carry a bacteria in the genus Blochmannia. The bacteria absorbs some of the nutrients the ants ingest, and in turn produce essential amino acids and other nutrients. Neither one can live without the other, an arrangement called obligate endosymbiosis (“endo” meaning internal or inside, and symbiosis being the name for any arrangement between two species).

There are over 1,000 species of carpenter ant in the world, in the genus Camponotus. The most common species here in the east is C. pennsylvanicus, the Black Carpenter Ant. They forage mostly at night, though are still often seen during the daytime. Reproductive individuals are produced by the colony in spring, usually May or June, in large swarms similar to what I observed with the citronella ants. Both sexes have wings, with the new queens being larger. The worker caste has two sizes of workers – “majors” that have huge heads and mandibles, and “minors” that are smaller. The majors are capable of giving a sharp bite, made more painful by the injection of formic acid into the wound. This same formic acid is often put to use by birds by picking the ants up in their bill and crushing them, then running them through their feathers (or by squatting on an anthill and allowing the ants to bite their feathers). The purpose of this behaviour, called “anting”, is often disputed, but is sometimes regarded as being a form of parasite control (such as feather mites, which can potentially destroy feathers). Julie Zickefoose recently did a post on a Black-throated Green Warbler anting in her yard.

Bizarrely, I don’t have any photos of carpenter ants themselves, despite how common they are. It’s one of those funny situations, you take lots and lots of photos of all the rare and unusual things you encounter, but never think to take a photo of the common stuff.