bugs – Page 26

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!

Flight of the queens

Yesterday while taking the puppy out for her hourly bathroom break, I happened to notice a few swarms of insects crawling among the grass on the lawn. Closer inspection revealed them to be ants. They were reasonably contained to a small area, perhaps a foot square, for each swarm, and there were at least three or four that I noticed. They seemed to be mixed individuals, half small yellow-orange ones, and half larger reddish ones with wings. Sprinkled among them were a number of small black ones with wings.

It was the makings of a reproductive flight, and the participants are most likely of the genus Acanthomyops*. Late in the summer, on a warm, humid day, often just after a rain, these ant colonies send forth their reproductive individuals to fly, mate, and establish new colonies. The little yellow individuals are workers. They won’t be going anywhere; once all the excitement is over they’ll return to the nest and get back to business. The larger ones, though, with the big clear wings, are the new queens, and the little winged black guys are the males.

*Myrmecos comments to suggest the ants are Lasius claviger, which used to be Acanthomyops but scientific evidence showed that the species actually belonged to the closely related sister species Lasius.

They have evolved this strategy of all swarming at once for two primary reasons. The first is that if everyone comes out at once it makes it a heck of a lot easier to find a mate. Just within our little lawn there were several colonies producing reproductives that afternoon. The other reason is the whole safety in numbers premise – if everyone comes out at once, it’s impossible for predators to get everyone, so some individuals will survive to start a new colony. These swarms are sure an impressive and intriguing sight, it’s easy to sit for a while and watch them all crawling up and around and over.

Curiously, when I was looking up on BugGuide.net for more info on the genus (they don’t offer much, unfortunately), I discovered this photo of the same sort of Acanthomyops ant swarm, which was also taken yesterday. The photo was from Connecticut, which presumably had shared similar weather patterns to us here. I wonder just how many colonies were swarming yesterday afternoon?

The common name for ants of this genus is Citronella Ants, for the smell they emit when disturbed or crushed. I didn’t know this when I was looking for them, so didn’t check, but wasn’t likely to stick my hand in there anyway. They don’t have the formic acid defense that the most common household ants we encounter do, but I didn’t know that at the time. Another name they’re known by is Foundation Ants, for their habit of nesting in the loose soil that frequently surrounds the foundation of suburban houses. Unlike carpenter ants, however, they are harmless and don’t do any damage to the house, nor do they tend to forage inside.

The queens head for tall objects sticking up from the ground, such as twigs or blades of grass, from which they take off on their flight in search of a mate. Once they’ve found a male and mated, they’ll drop to the ground and look for a suitable, uninhabited location to start a new nest. The soft soil around foundations is easy for the young queens to dig in, which is why it’s so often favoured. Once the queen finds a spot she’ll drop her wings and start excavating her new home. It’s a lot of work, and will take her a while to establish. Many nests never make it past this stage.

Some species of ant, including Acanthomyops latipes (I don’t know if these are that species, or a different species of Acanthomyops), will avoid having to go through all that work by instead searching out a colony of the closely related genus Lasius. She’ll invade the colony, kill the Lasius queen, and take over control of the existing workers while she breeds a new colony of her own offspring. This behaviour is called temporary social parasitism. In fact, because of this close relationship between these two genera (as well as other reasons), Acanthomyops is sometimes considered a subgenus of Lasius, rather than a separate genus in its own right.

This little male looks tiny next to the large queens. The males, unlike the queens, will retain their wings till death, but that’s not all that far away. The male’s sole purpose appears simply to mate with new queens, after which he dies. While queens may be produced by young colonies, males are apparently only produced from older, mature colonies. A colony may last for many, many years, depending on the species. A queen will live for several years herself (up to 15 years depending on the species), but for older colonies it may not be the original queen present; rather, she may have died and been replaced by a daughter.

Not sure what this worker is doing. In fact, I’m not sure why the workers were out amid the swarm of winged reproductives period. I didn’t spend a lot of time watching them, because I had a rambunctious puppy at the end of the leash who didn’t have the same appreciation for such phenomena. I put her in her crate so I could take a number of photos of the colony, but couldn’t leave her there long. When I returned to the area this afternoon they were all gone, the area was empty. It’s amazing how fleeting it is, and you really need to be in the right place at the right time to notice it. Presumably a number of those queens I saw yesterday are now off starting a new nest of their own.

International Rock-flipping Day

Today was the second annual official International Rock-flipping Day, which I first mentioned back in this post. Dave at Via Negativa has begun collecting the posts by people who have participated and compiling them at this post on his blog.

I headed out just after noon, after temperatures had warmed up a bit. Rocks are in no shortage at our house. I started with a few up by the house, not finding a whole lot. A few millipedes (which are everywhere, a couple earthworms, including one giant fat one, and a cricket. The most interesting thing under these rocks was what appeared to me to be a beetle larva of some sort. After flipping through the beetle section of the Kaufman guide to insects, I’ve changed my mind, and now think it’s a rove beetle, possibly Platydracus maculosus, a widely-distributed, decay-feeding, short-wing-covered (but deceptively long-winged) beetle. I love the woodgrain patterns in it.

I headed down the hill, flipping a couple rocks in the forest. I expected a bit more from the forest rocks, since the forest always seems like such a rich habitat. You’d think there’d be lots of stuff munching on the deliciously rich detritus layer of the forest floor. But the rocks in the forest area were decidedly empty. The only really interesting thing was the below… white thing. It looked like it was probably a type of millipede, but it was very pale, paler than any millipede I’d ever seen.

I carried on and found this promising looking rock, above, sitting beside the base of a tree, near the forest edge and not far from the water. Indeed, when I flipped it over it had much more under it than any of the rocks I’d checked to that point. First thing I saw as a largeish spider, mouse brown with interesting darker markings. Again, no idea what it was. You know, the primary thing I learned about this whole exercise was how little I knew about most invertebrates. Particularly the rock-dwelling sort.

In there with the spider was the above slug. Apparently there are several types of slugs, and many of the most common ones are introduced. Who knew? This could be an introduced slug. It could also be a perfectly natural native slug. I have no idea. My guidebooks don’t do slugs. The most interesting thing under that rock wasn’t the spider or slug, but rather what looked a bit like a fungal garden of an ant colony. Aside from the fact that I didn’t see any ants, except one that ducked into the large hole in the ground. But all the tunnels that weaved in and out of the surface were suggestive of an ant colony, and the fungus looked like it was associated with it. It could have been complete coincidence, of course. Either way, it was an interesting rusty colour.

The best was saved for last. I ended up at the edge of the lake, where a portion of our shoreline is built up with large rocks. I flipped a couple of small ones, with no notable findings, before landing on a nice large, flat slab, resting on a sandy base. The treasure trove, such as it was, laid under here.

Although I’d seen a couple others under earlier rocks, there was a nice big, grey isopod under this rock. Which sat there quite obligingly, not something most will do for me. These aren’t insects, but rather are crustaceans. They like damp places, so are often found in basements or bathrooms as well. I bet you didn’t know that the extremely common pillbugs (without tails), and sowbugs (with two “tails”) such as the above, are all introduced from the Old World.

This beetle went scurrying before I could get a good picture. Darkling beetle of some sort, maybe? Or possibly a ground beetle such as Pterostichus sp.? It’s too bad I didn’t get a better photo, but then – I’m not sure it would’ve done me a whole lot of good anyway. There are so many beetles (Kaufman dedicates 90 pages to the group) and I don’t know enough about them to be able to differentiate between species that have similar shape and colouration.

Likewise, I didn’t get the best photo of this one, either. They move so fast! And you’re hoisting the rock up with one hand while scrambling to get the camera positioned with the other. I thought at first the shape of this one suggested tiger beetle, but I don’t think the head is big enough, and it doesn’t have spots. Now I’m thinking a type of ground beetle (it helps that it was fittingly found on the ground), perhaps an Agonum sp. such as Agonum cupripenne? This one has the look of iridescent-purple wing covers and an iridescent-green thorax, which the A. cupripenne images on BugGuide.net show. However, there are over 50 species in this genus in the northeast.

And lastly, my favourite bug of the whole outing. Also scurrying for cover, its wing covers spattered with droplets of water. Rain, perhaps, since it was raining lightly, briefly, before I stepped out. I’m fairly confident in calling this one a Bombardier Beetle, of the genus Brachinus. The members of this genus have the fascinating ability to spurt boiling hot liquid chemical from its abdomen, scalding the potential predator so the beetle can make its escape. It accomplishes this by combining two liquids (hydrogen peroxide and hydroquinone), contained in separate compartments in its abdomen, as it shoots them out at the threat. The liquids undergo a chemical reaction with the aid of a catalytic enzyme (an enzyme that acts to initiate or speed up the reaction), and rapidly reach a temperature of 100oC (212oF). In addition to scalding the skin, the chemicals can also stain it yellow. The species in this genus all look very similar – black wing covers, orange thorax and head – such that I have no idea which particular species this is. There’s 40 to 50 species in North America, usually found under things, like rocks, in damp areas at the edges of floodplains or water bodies.

And that wraps up IRFD 2008. Don’t forget to check out the official page for other posts!