Lots of pictures today! But first, some garden stuff…which is what this blog is really supposed to be about, after all.
The ‘Black Peony’ poppies and the Nicotiana ‘Chocolate Smoke’ have opened. Neither is as dark as I expected or would have liked, but that may change. The nicotiana is an intriguing shade of reddish brown, like dried blood, which I actually find more interesting, so I’m not disappointed.
That dill plant is oddly popular. In the past few days I’ve seen ladybugs trundling up and down it, and most recently a cluster of eggs. Funnily, there’ve been very few aphids on it (even before the ladybugs showed up). I like ladybug larvae. The geek in me is reminded of Battra, although the resemblance isn’t really that strong. It would be nice to have some anyway, to move to the rosebushes. Those always need an aphid patrol.
I’ve noticed a few sumac seedlings showing up, probably staghorn sumac (Rhus typhina), because those are very common around here. They favour disturbed sites (such as urban and suburban landscapes) and they’re very tough. I usually pull them up immediately, because while it’s a very attractive small native tree, it has a tendency to sucker and spread aggressively. It’s sometimes used to reclaim and stabilise slopes quickly. However, it can also serve as a host plant for the Luna Moth (Actias luna). I’ve never seen any of those around here, but given that I don’t have their host plants and the adults fly at night, that’s not surprising. They are listed as being in the area, though. I’d love to raise a few just once. I think I might try growing one of those sumacs in a large container and see what happens.
A Monarch update: on Day 31 since the egg was laid, or Day 12 since pupation, the chrysalis is beginning to darken. This is actually the wings becoming complete and the colours and pattern showing through the translucent cuticle. You can see hints of orange in the picture. You can also see I’ve moved the chrysalis from the piece of cardboard it had formed on. I often do this, because Monarch caterpillars delight in choosing inconvenient places to pupate. I reckon eclosure in two to four days.
The Eastern Black Swallowtail caterpillar beginning its own pupation. Here it’s just resting, preparing for the big event.
Eventually it spins a network of silk along a twig or stalk as an anchor. At the bottom it spins a small pad that it grasps with its anal prolegs; about a third of the way from the top it spins a loop of silk called a girdle.
In this picture and the next, the caterpillar is contorting itself as it slips its head and thoracic segments through the girdle. This is new to me – I’d always thought that it simply spun the loop around itself.
Literally seconds later, it assumes its rest position. I’ve left this and the next few pictures at a larger resolution so you can see the silk network covering the side of the dill stem as well as the girdle and pad.
And six hours later its body has changed as it approaches its final ecdysis. The body has contracted in general and the prolegs (the fat stumpy legs) have shrunken and withdrawn. The hindsection is now tapered and the whole thing is in a characteristic comma shape.
About nine hours later the posture is the same, but the outer cuticle is translucent and beginning to separate from the inner skin. You can just see the texture of the upcoming pupa under the skin.
Dammit! In all the caterpillars I’ve raised, I’ve never managed to catch one in the process of shedding its skin. Granted, I do have other things to do, but still… Anyway, four and a half hours later I walked in to find this, and the exuvium (old shed skin), still moist and fresh, lying in a heap underneath. This is definitely one moult I’d like to witness, because I’ve always wondered how the skin slips off under the girdle, and if the head bends back before or after.
Thirteen hours later and the chrysalis has composed itself, changing shape slightly yet again, as well as colour and posture.
Some EBS caterpillars pupate green and yellow, and some mottled brown. I’ve seen all sorts of explanations about what determines it, although crypsis is the obvious reason. It just so happens that in these two examples the pupa matches the twig/stem it’s on, but that’s not always the case. I’m most inclined to agree with the explanation that it’s determined by genetics and driven by natural selection…like evolution in general.
Similarly, the EBS caterpillars occasionally show colour variations. Most are light green with black and yellow bands, but a few rare ones have more black on them. Out of nine EBS caterpillars this year, this is the only black morph; some have even more black. It doesn’t seem to have anything to do with the colour of the eventual chrysalis.
And finally, here’s a picture of the Milkweed Tussock Caterpillar, which in adult form is known as the Milkweed Tiger Moth (Euchaetes egle). Funky, no? It is one of the few Lepidoptera outside the Monarch genus (Danaus) that feeds on milkweeds (Asclepias spp.).
Back to the EBS pupae: it’s still fairly early, so they’ll probably eclose in about two weeks, possibly a bit more because we’re having a cool summer. It’s also possible that they’ll enter diapause, or dormancy, and overwinter as pupae. This is more likely in the ones that pupate later. In that case they won’t eclose until spring.