Sunday, November 9, 2014

Giant Swallowtails

Something exciting happened in our yard this summer. In late August, as I sat, contemplating the garden and enjoying a sunny afternoon, I watched 2 Giant Swallowtail butterlies lay their eggs on our 3 small Hop Trees. We planted these trees the previous summer in the hopes of attracting this magnificent butterfly. Last summer we had a visit from an older worn Giant Swallowtail, our first in the garden!

This is the largest butterfly species in Ontario and it is expanding it’s range northward. The host plants for the larva in the northern part of its range are Hop Trees, Meadow Rue and Gas Plant. In the south it loves citrus trees.

I checked the Hop Trees and found the tiny eggs scattered about on the upper side of the Hop Tree leaves. They are around 2 mm in diameter and orange coloured.

After approx. 1 week the eggs turned dark, likely transluscent and showing the dark larva within.
One morning I noted that tiny 2-3 mm long dark brown and cream caterpillars had hatched. The first thing they do is eat the egg casing for nourishment, then they begin eating the leaves.
I watched them go through several instars, shedding their skin then turning around to systematically eat it. Again nothing wasted. They rested frequently for long periods in the daytime, immobile on a leaf, preferring to eat at night. The first instars look very convincingly like fresh shiny bird droppings, a deterrent to predation. 
The last instars looked rather like the head of a small snake. Most were approx. 5 cms long.

At one point after 2 weeks I noticed that 2 of the largest caterpillars (the first ones to hatch out) were gone, they likely left in the night to find a place to pupate. They will pupate on tree branches as a chrysalis.  We have 1.4 acres with many trees so it was impossible to find them. I found out that since these butterflies are at the northern limit of their range, it is not clear if they can survive overwintering in the pupal stage, without some protection from the elements. 

With that in mind I decided to collect them before they all left. Out of 8 adult caterpillars I  managed to collect 5 caterpillars before they left. The fate of the 3 who went off in the yard is unknown. Perhaps they will survive and hatch out in the spring.

Of the five caterpillars I rescued, 4 are now in the pupal stage on small branches in special wooden boxes with a mesh door. Sadly one died after feeding for 2 weeks on a daily diet of fresh Hop leaves, until the leaves turned yellow and dropped. It was in the last instar, but one morning it was dead.
Chrysalis looking like a broken bran

The 4 surviving pupae are in an outdoor shed, protected from the bitter winds, precipitation and rodents. Exposure to freezing temperatures will initiate diapause and they will hopefully overwinter in the chrysalis stage till spring when they should hatch out as butterflies!

More on that come spring. 
Amazing the wonders you come across when you just sit watching nature...

Enjoy the small pleasures.

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