invertebrates – Page 26 – Seabrooke Leckie

Today at Kingsford

My mom was up today and as part of her visit we made the obligate trip down to the lake. My trips to the water have been more sporadic lately as the weather cools, particularly during rainy periods, which it has been lately. The few trips I have made have been to the boat, and then across the lake. So I hadn’t been paying too much attention to the vegetation and goings-on in the immediate vicinity of the dock.

My mom pointed out some leaves, fallen from the huge tree on the shore, which had a gall at the base of the stem. I believe the tree is an Eastern Cottonwood, towering probably close to 100 feet, with a thick trunk several feet around. The galls, after looking them up, I believe are the result of the Poplar Petiolegall Aphid (Pemphigus populitransversus).

This aphid has a complicated, two-part life cycle. The first stage starts with the female aphid, sometime just as the leaves are beginning to grow, burrowing into the leaf petiole (the stem), right at the base of the leaf itself. This intrusion causes the tree to form a gall around the wound in an effort to contain the attacker. The gall is hollow, and inside she lays eggs which have developed into winged adults by summer.

Around July here in Ontario, these new adults leave the galls and fly out in search of plants in the Brassicaceae family, which includes commercial vegetables such as cabbage, cauliflower, beets, turnip, radish, and others. These adults burrow into the soil and feed on the roots of the plants, but only cause serious commercial problems when the vegetables are planted late such that the roots are young when the aphids discover them (thereby stunting the growth). Well-developed plants are not bothered much. They reproduce parthenogenically – meaning the females create clones of themselves without mating.

The aphids spend the winter buried up to 20 cm (8 inches) deep (according to two sources; one says they return to the tree to lay eggs). Winged adults are produced either in late autumn or in the spring (it’s not clear with the two sources, but the one that has them returning to the tree in the fall obviously requires winged adults in the fall), which return in spring (or the fall, in the case of that one source) to the poplars and lay eggs in the crevices of the bark. These eggs grow into more reproducing individuals, but in this case the female lays only a single egg on the stem of a leaf, which becomes the aphid that burrows into the petiole and starts the cycle all over again.

Something like that, anyway. It seems that the life cycle of this species is still a little fuzzy. These aphids inside the galls seem out of place based on what I’ve read. Are they just late summer aphids that never made the trip to their winter roots? Or that got started late and plan to head out soon? There were some winged individuals in the galls. Or do some spend the winter in the leaf gall instead of the soil? Maybe some adults return there? The gall, rather than having an open hole, had a sort of cap formed from a folding-over of the petiole, that would keep it snug. My web sources don’t say, so perhaps it will remain a mystery.

Buried seashells

This afternoon, Blackburnian suggested we take Raven across the lake to the park and do some exploratory hiking. I thought this was a great idea, so we bundled Raven into her harness, hiked down to the boat (now no longer docked at the dock because the water level has gone down so much from dam control that the dock is surrounded by mud), and boated across to the park.

We had a great hike. Surprisingly, this is the first time I’ve gone over and hiked around myself, though Blackburnian’s been there a few times. For whatever reason, I’d just never made it, other things had come up. So it was nice to see a bit of the park interior. I’ll elaborate more on the hike tomorrow.

One of the things we came across while hiking, though, was this underground paper wasp nest. Aside from the fact that it was a wasp nest built of paper underground, we really had no idea what it was. So I snapped a few photos, with the intention of looking it up when we got home. The wasps were totally unconcerned with us being there, and me nosing up to the mouth of the burrow it was set in so that I could take photos. They just went about their business, popping inside the entryways in the paper, one or two flying away while I squatted there.

I was surprised to find, when I got home, that this was the nest of Eastern Yellowjackets (Vespula maculifrons). I don’t know that I’ve ever consciously looked at a yellowjacket and thought, “that’s a yellowjacket,” so I’m not sure what I was expecting. Something more yellow, maybe. I knew yellowjackets primarily nest underground, but for some reason this didn’t twig with me. Plus, yellowjackets have a ferocious reputation, and here these were, apparently unconcerned. Nevertheless, the wasps in this burrow were Vespula.

Yellowjackets as a group build paper nests using wood and plant fibers mixed with saliva. They can make some beautiful patterns in the paper they create, scalloped sea-shells of grays and whites. They’re a social species, like many of the Hymenoptera, with a single reproductive queen cared for by many female worker offspring. Although the larvae are fed bits of chewed-up insects, the adults themselves feed on nectar from flowers. They’re also not opposed to visiting sugary drinks, and are probably the wasps most commonly seen crawling into pop cans.

The colonies never survive the winter, despite being nestled underground. In the fall, male drones and young queens are produced from the colony, and these then fly away to mate. In the photo above you can see three workers, the slightly smaller ones with more yellow, and one male, the slightly larger one with more black, on the left. The new queens will mate with the males; the males will then die, while the queens find a safe place to hole up for the winter. They are the only ones to survive. Come spring, they find themselves an abandoned burrow, and start up a new colony. They begin from scratch, and the first brood is completely cared for by only the queen. Once she’s raised a few workers, she settles in to her role as egg-layer, and her daughters run the nest. By the end of the summer the nest may hold up to 5,000 individuals.

Interestingly, all workers are females because they are diploid – having two sets of chromosomes. Males are created through the laying of unfertilized eggs (the queen, who holds the sperm from her mating the previous fall in a storage chamber in her abdomen and doles it out according to the gender of offspring needed), and are therefore haploid – have just one set of chromosomes. New queens are diploid females that are fed a special concoction (in honeybees, called “royal jelly”) that promotes her development into a reproductive individual.

I gather the workers will sting if provoked, and their sting can be acutely painful. However, probably just walking by won’t provoke them. On the other hand, the juicy, tender larvae are a favourite delicacy of bears, skunks and others, who will endure the workers’ stings for the treat. As long as you’re not digging in to the nest for a snack you’re probably fine.

Web masters

Today was the first day of fall, as of 11:44 morning. It’s interesting how “they” know with such precision just when summer rolls into fall. It’s always seemed to me that the calendar’s division of the seasons is so arbitrary, segmented into three-month blocks that were chosen to most closely approximate the time of year they represented. But the actual seasons are defined by something much less tangible than dates on a calendar. Technically fall only just arrived today, but for me, it’s been fall for the last three weeks. You can smell it in the air.

There’s always the cues from nature, of course. The changing colours of the trees. The goldenrods and asters blooming. The birds and monarchs heading south. The shortening days and cooler nights. Now, one would figure that the critter ensconced in the wispy cobwebs above would fit into this category, as well, simply by its name – the webs were made by the caterpillars of the Fall Webworm, Hyphantria cunea.

These particular photos were taken when I visited my parents’ a couple weeks ago. It was the second week of September by then, but many of the webs were empty, their occupants departed, and had probably been there for at least a couple weeks already. I had noticed some on the road near my own home at the start of September. It would seem a portent of the impending autumn that the webs should show up at the beginning of the month like that, and I rather suspect that, even though they can be observed year-round in some areas, they really are most frequently seen in the fall, hence the name.

The Fall Webworm is a moth, the adults varying from all white in the north to heavily spotted with black or brown in the south. It’s a type of tiger moth, which includes many hefty-bodied species that don’t resemble tigers at all. Despite the superficial appearance of the nests to those of the Tent Caterpillar, they aren’t closely related. You can tell whether your infestation is of tent caterpillars or fall webworms, for one, by the time of year. Tent caterpillars are springtime species, while the webworms, as their name implies, are a fall species. Also, tent caterpillars usually build their nests in the crotch of a branch, and it rarely gets much larger than a foot across for the largest.

Webworms, on the other hand, start out at the end of a branch. The female moth lays up to 1,500 eggs on the underside of a leaf, covering them with hairs from her abdomen to protect them while they develop. The larvae hatch and begin spinning a silk web containing the surrounding leaves. While tent caterpillars march out several times a day, following silken trails, to munch on leaves, the webworms wrap their food inside their web so they remain more protected. The downside to this approach, however, is that once the leaves inside the web are all eaten, they can’t just change the trail they follow. So they end up expanding their nest to encompass more leaves, and then even more. By the time they’re ready to leave the nest they could have wrapped up the entire branch. A very large colony of webworms is capable of enshrouding the full tree. Sometimes very large trees, like the one in the first photo that was nearly as tall as the nearby telephone pole.

Caterpillars go through 11 instars, or larval stages. There are two different, distinct races, distinguishable by the colour of the head: larvae of the north have a dark head, while those of the south have a reddish-orange head. Northern caterpillars also have white hairs coming out of black and orange bumps, while southern caterpillars have brown hairs coming out of reddish-orange bumps. Earlier instars are generally paler.

Like with the tent caterpillars, the webworms rarely kill their host trees, even though they may completely defoliate them and leave them looking barren and dead. Because their timing coincides when the tree is starting to wrap up its growing season and thinking about dropping its leaves anyway, it doesn’t lose a whole lot (tent caterpillars work the other way; they eat before the tree gets going, so it still has time to recover during the summer). Webworms are generalists, not targeting any one specific type of tree; their larvae have been recorded on 120 species of tree and shrub in North America.

It’s found right across North America, from southern Canada south to northern Mexico. However, it’s also found in Europe, as a non-native invader. It was introduced to Yugoslavia sometime in the 1940s, and has since spread to encompass much of the continent. It was also introduced to Japan in 1945, later spreading to China and Hong Kong. Throughout its entire range it’s been documented on 636 species of trees, and is considered one of the most, if not the most, polyphagous of insects (fancy scientific name for generalistic feeders). Basically, anything deciduous is fair game.

Most of the caterpillars have left their nests now, the webs empty of larvae or leaves, just frass remaining, trapped between the web layers. They’ll trundle off to find a safe place to pupate, in the bark and leaf litter at the base of trees. There, they’ll spend the winter, cozily wrapped up in their silken cocoon, interwoven with bits of detritus from the soil. Next spring, the adults will emerge, once the risk of frost has passed, around May here at my latitude, and they’ll start the cycle again.

There and back again

Yesterday morning I did the bird census down our road. It was a lovely morning, cool, but not unpleasantly so, clear and sunny. As the sun rose, it warmed up, so by the time I got down to the meadows at the end of the census route, it was feeling pretty comfortable. Perfect weather for migration. It wasn’t just the birds who were on the move, though – so were the monarchs. I haven’t seen very many monarchs since arriving here, just the odd one here and there. Yesterday morning I probably saw about a dozen during the census – enough for me to note their increased abundance.

In northern climates, where the environment cools down or freezes during the winter, animals have evolved various ways of coping. For insects, most of which are unable to be active when it’s very cold, there are two strategies, stay or leave – overwinter (essentially a hibernation of sorts) or migrate. Monarch butterflies fall into the latter category. Monarchs are long-distance migrants, and the individuals I saw in the meadow yesterday will, in a few months, be spending a nice balmy winter in central Mexico.

There are three distinct populations of monarch butterflies – one east of the Rocky Mountains, one west, and one in Central America, all of which have unique migration patterns and overwintering destinations. About 90% of Canada’s monarch population live east of the Rockies, and all of them will head down to one of perhaps a dozen spots in central Mexico to spend the winter. These sites are all high-elevation oyamel fir forests located within about 800 square kilometers (309 square miles). This area has been designated as the Mariposa Monarca Biosphere Reserve.

The population from west of the Rockies winters further north, in central and southern California. There are about 200 known overwintering sites in the state, with anywhere from dozens to tens of thousands of individuals present at each site. The Central American population doesn’t undertake a latitudinal migration, but mostly moves short distances of 10 to 100 km (6 to 60 miles) from highland to lowland areas.

Not surprisingly, with populations overwintering in such concentrations, both habitat loss and natural disaster pose serious potential threats. I would be extremely surprised if the population hadn’t gone through such events before, and obviously had survived and rebounded, but it does pose some concern, especially in the face of climate change that has the potential to produce more numerous and more severe storms and conditions than the butterflies are used to weathering.

A monarch butterfly hatched at the beginning of the summer may only live for two months, but those hatched at the end, the ones that undertake migration, will enter a non-reproductive state that allows them to live for up to 9 months, enough to get them through the winter and started back north to breed again. Of course, it’s not enough to get our Canadian butterflies back home to us, so those monarchs that I saw in the meadow will not return. Rather, monarchs have developed a strategy to circumvent this short lifespan and still allow them to migrate. The butterflies that overwintered in Mexico will move north to breeding sites in the southern US in March and April. There they lay eggs and go through two or three generations. The latter generations are the ones who continue the push north, as the original adults by that time have died. This step-by-step generational approach to migration allows the monarchs not only to take advantage of milkweed as it starts growing in each region, but also helps to build up the population, which suffered losses over the winter. As well, by going further north, the species can produce up to three additional broods beyond when milkweed begins to die off in the southern US in June.

Our Canadian monarchs finally make it home in late May or early June. Those west of the Rockies may not return to British Columbia in all years. The best years are warm, dry summers, or summers with extended periods of sunny weather. The mechanisms by which the later generations find their way back north again is still unclear, but there is obviously a genetic component to it.

During southbound migration, monarchs prefer to stick to dry land and are reluctant to cross large bodies of open water (such as the Great Lakes). Part of this is because of their migration method – they use air thermals, rising columns of warm air heated by the sun striking the earth, to gain altitude, where wind currents higher in the sky will help give them a tailwind, or where they can glide down to the base of the next thermal (much like hawks). These thermals can sometimes take the butterfly to incredible heights – sometimes up to a kilometer (0.6 mile) high.

Air thermals don’t form over open water, so it’s much more work for the butterfly to cross a large lake than it is for them to follow a shoreline. However, sometimes following a shoreline leads them into what are often called migrant traps – places where the geography of the land naturally causes migrants to accumulate (this applies to both birds and butterflies). Because going in reverse counters their natural instincts, the migrants remain at the trap until such time as favourable weather occurs for crossing over the lake. Sometimes this is simply the next day for butterflies, if they’ve arrived mid-day, or sometimes they may hang around for a few days, if a string of cold or wet days occur.

One such migrant trap is the Leslie Street Spit (Tommy Thompson Park) on the Toronto waterfront. Although I was away most years, I was fortunate to be able to experience the migration last fall. Often monarchs will make a significant push on just one or a few days, leading to huge concentrations (for here, anyway; they’re paltry compared to those on the wintering grounds). We lucked out in catching the one big one last fall – we’d noted increased numbers of monarchs passing through earlier in the morning, and later in the day a trip to the tip of the spit revealed clusters of butterflies clinging to the tree branches, waiting for the next day to cross the lake.

We estimated there were perhaps 15,000 to 17,000 butterflies out there, split up over three or four locations, but with at least two thirds of them in a single large woodlot at the end. It was an amazing sight, but interestingly, a surprisingly cryptic one. When we first approached the woodlot we weren’t sure there were many butterflies there. It wasn’t until we actually walked inside amongst the trees, and disturbed a cluster, that we began to notice them. Then, once we started really looking, they were everywhere. Walking through from one end of the woodlot to the other was magical; as you passed the butterflies would rise from the branches where they were hanging and filled the air in golden clouds, before settling back down again once you’d passed. So light on their wings, it gave the space a more airy feeling than if it had simply been empty.

I probably won’t see numbers like that again without a special trip down to Lake Ontario; although monarchs will still roost together in smaller groups, such migrant traps just don’t exist away from the lakeshore. But even still, watching the butterflies dance among the meadow flowers is also very captivating and peaceful.

You can join in and help track monarch migration with the citizen science program Journey North, which invites you to submit your monarch observations to be included in a map compilation. The site also has lots of other great info about monarchs and monarch migration, including maps of this year’s migration.

Today at Kingsford

Another “Today” today, due to technical problems. I was out most of yesterday afternoon running errands in town (a task that seems to suck up most of a day without any trouble at all, as what should reasonably take less than three hours ends up taking over five – time must stretch in Kingston) and when I returned home, the internet was not working. Well, as I’m sure everyone can sympathize, trying to troubleshoot computer problems can take a while. I did finally get it working again this morning, but only after reinstalling the program (which, it turned out, had mysteriously disappeared). This afternoon was spent checking out my parents’ soon-to-be new digs, so no time for a full post tonight, either.

Time for a short one, though. This evening I discovered this guy resting on the wall beside the door. I suspect it’s the same one that startled Blackburnian yesterday and then disappeared. Although it looks like a giant mosquito, and looks rather creepy, it’s not, and it’s harmless. It’s a Crane Fly, a member of the family Tipulidae. The Kaufman guide to insects notes, “Often abundant, and extremely diverse, they are impossible for anyone but an expert to identify beyond the family level.” Well. Should I not even bother trying, then? Still, those wings ought to be distinctive, such bold patterns and bright (for a crane fly) colours. And the size. This is easily the largest crane fly I’ve ever seen, a couple inches across from leg to leg.

Sure enough, a search for “giant crane fly” on BugGuide.net turns up several photos of my bug in the results. It’s a Giant Eastern Crane Fly, Pedicia albivitta. It’s found through most of the northeast, south to North Carolina and west to Minnesota, so strange that I haven’t encountered it before (a little like the millipedes, I suppose). The larvae are aquatic and predaceous, feeding on small invertebrates. Adults are seen in two distinct flight periods, one in the spring and one in the fall. They also come to artificial light. Guess we’ll be seeing a lot of them!