August 7th, 2006
a boy and two girls
Before I move on to other things for today — that’s assuming I manage to get my other post written — here is an update on the Monarch caterpillars.
Amazing as it may seem, I managed to miss *another* caterpillar’s transformation to a chrysalis last evening even though I was around the house (arrrrrgggh!!!). If you’ve been following this Monarch story for the past week, you’ll know that I’ve missed two before this one. Oh well, as Don remarked this morning, “With all of these caterpillars in the house, you’re bound to see one sooner or later.”
Anyhow, back to the news. Using my loupe, I inspected each of the pupae this morning. It appears that the first pupa will be a male butterfly, and the second and third will be females — at least, according to a page on sexing Monarchs on the MonarchWatch.org website. If you look closely at a chrysalis, there are a series of rings at the end closest to the cremaster (the black piece that attaches the pupae to its silk mooring). The rings are referred to as abdominal sternites. If the ring adjacent to the last of the paired black dots is divided in line with the center of the pairs of dots, the pupa is a female. If it is not divided, then it is a male. Above, I’ve shown the section of both pupae with the rings. On the left, is the female with a small arrow pointing to the division in the ring. On the right, is the male which has no similar division (click on image to see a larger view).
In other news, I brought another 12 larvae indoors last evening. I haven’t yet done this morning’s head count, but everyone looks to be doing well and I believe the number of larvae is currently around 30 or so, plus 3 chrysalises. Last night, while looking around for larvae, I found a couple of small ones that were in the process of being consumed by Stink Bugs, and the remains of another large one that had fallen victim to a predator. There was also plenty of evidence of hatched larvae such as chewed milkweed leaves and caterpillar frass on many plants, but there were very few “survivors” to be found. It seems that the life of a Monarch caterpillar is fraught with great danger.
Well, that’s about it for the Monarch report. I’ll try to put up something non-Monarch-related later today.
August 7th, 2006 at 1:53 pm
Great documentation, Bev. This is turning out to be such a fantastic experiment. I’m sure you’ll see one cat transform into a chysalis. I won’t even mind if you don’t film it for us– your description will be so thorough and exact. It did just occur to me that you haven’t mentioned seeing any chrysalis outside. Monarchs really do have the odds stacked against them, don’t they?
August 7th, 2006 at 2:03 pm
Very interesting!
I always beleived that monarchs didn’t have many predators – even the site you linked to said that not much is known about invertebrate predation.
August 7th, 2006 at 3:52 pm
Robin – Thanks! Yes, this is turning out to be a neat experiment and I’m learning so much as I go along. You’re quite right about me not having found *any* chrysalises outdoors. I was just thinking that last night as I thought I’d encounter at least a few. However, having seen how so many signs indicating that larvae have been killed by predator insects, I realize that the number of caterpillars that “make it” must be just a tiny fraction of whatever hatches. It’s really kind of amazing that the species has survived considering the risky nature of their life history and especially their migrations.
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Laura – I had no idea they had so many predators until this week. I’ve always heard that birds didn’t bother then because the larvae fed on milkweed. I suppose that’s true of the birds, but not true of the insect predators. I’ve found quite a number in the midst of feeding on Monarch caterpillars, and they don’t seem to be at all deterred! I’m probably going to do a post on preadtory Stink Bugs in the next couple of days and will illustrate that some of the photos I’ve been taking.
August 8th, 2006 at 9:58 am
Nice photos of sexing what’s inside the chrysalis! And all those structures have names, too. I was wondering what the black pigmentation was called – it was so regular.
Do you know if the chrysalis of other butterfly species have the same structures?
August 8th, 2006 at 10:43 am
Wayne – Most of the structures do seem to have names, although I haven’t yet found a name for the “black dots”. Seems like everyone just calls them that. Same goes for the gold spots. I did come across something interesting regarding chrysalis pigmentation. One of the experiments done by a class that raised monarchs was to try to remove the gold spots on part of several pupae to see what would happen to the adults. Apparently, it seemed to damage the wings. However, I’d almost think that that might have happened to the wings from the actual process of removing the spots — they used a surgical cauterizing tool) – and I suspect that touching almost any point on the chrysalis might have caused damage. Anyhow, I’ll be watching for more info on pupa anatomy. I do think the chrysalis of other butterfly species would be pretty much the same as the monarch as far as the anatomy goes, although the shape and attachment to host plant, etc.. might differ greatly. I haven’t checked enough other pupae to know, but I’ll try to pay attention to such things in future. Again, this experiment has got me looking at caterpillars and pupae a lot more closely than before, so I’m learning some new things as I go (my “learn one new thing a day” has turned into more like “learn three new things a day”). (-:
August 8th, 2006 at 1:23 pm
Really have enjoyed and learned a great deal from your blog essays. I found this article in the NYTimes you might be interested in if you haven’t already seen it.
http://www.nytimes.com/2006/08/08/science/08cate.html
Excellent studies you’re doing!
August 8th, 2006 at 2:54 pm
Phil – Thanks, glad you’re enjoying the caterpillar posts. Great find on that article from the NYTimes! I very much enjoyed reading it! David Wagner’s “Caterpillars of Eastern North America” is just about my favourite among the field guides here at the farm so it was nice to read about him. He’s right too… this time of the year is about the best for finding interesting caterpillars – and spiders too. Btw, a note about the NYTimes article for anyone reading this – it requires you to register, but just takes a moment and its free.