Some eyespot humor

http://www.bitterfilms.com/anesthetics-eyespots.html

I found this comic particularly funny because it points to one of the main themes of my PhD:

Eyespots may not be effective predator deterrents.

There is some evidence supporting a protective effect of eyespots in butterflies (defection and intimidation), but until my work last summer there hadn't yet been anything more than anecdotal evidence showing a protective effect in caterpillars. Even my work last summer showed little protective effect of caterpillar eyespots; although there are a variety of interesting reasons why an effect may not have been observed (I'll go through these in detail later).

Aside: Deflection is a strategy where prey somehow direct or draw predator strikes away from vulnerable parts of their body (e.g. their head). Intimidation acts to prevent attacks altogether by making the prey look too dangerous or difficult to subdue.

Pinning up chrysalis'

A few days ago I pinned up the 5 Papilio canadensis chrysalis on the side of the screen tent that I have set up outside. I thought that it would be the best way to ensure that they experience natural weather conditions. Earlier I had relegated each of the large caterpillars to their own tupperware container (make sure to change the sprigs of host plant every day).

Once the caterpillars pupate I clipped the twigs and pulled off all the old leaves. Acctually it is incredibly important to remove all the dead leaves and caterpillar frass (caterpillar poo is called frass), especially after the caterpillar has pupated because this is really the only time that the frass is wet. If you're not careful mould will grow and you risk killing the pupa.

Swallowtail Cohorts

I have been talking about "cohorts" in my posts, but I should explain that I don't mean to say that these correspond with cohorts in the wild. I am using the term cohort to differentiate among the batches of eggs laid in captivity by different females this summer. Here in Ontario Papilio canadensis only has one cohort. According to the Ottawa Field-Naturalists' Club the flight season runs from mid-May and ends in early June. This is definately consistent with what I saw this summer in the field. For comparison, Papilio polyxenes has 2 flight seasons. One starting at the same time as Papilio canadensis (mid-May), ending before the end of June. The second cohort runs from mid-July and finishes at the end of August.

This information came from the "Checklist of the Butterflies of the Ottawa District" compiled by Peter Hall, Ross Layberry, and Don Lafontaine in August 1996. It has the flight seasons of the 80 most common butterflies. Maybe the best $2.00 I ever spent.

Papilio canadensis pupation & chrysalis

Here are some photos showing the pre-pupation and chrysalis of Papilio canadensis. These photos were taken today. The hanging individual below and the chrysalis are 2 different individuals.

Below you can see that the individual above excreted all remaining waste. The droppings from Papilio canadensis caterpillars are always very dry until this final excretion.

Below is the chrysalis of the individual which had turned brown two days ago. It is incredibly cryptic. It looks just like a broken branch.

Brown Papilio canadensis caterpillar

Today one of the caterpillars turned brown. This happens when they are preparing to pupate. I suspect that it also corresponds with a change in microhabitat use. The caterpillars do not grow much after they reach this body size meaning that thier habitat needs likely change from locations with abundant food sources to those that provide a safe place to pupate. Being green makes the caterpillar incredibly cryptic when it is amongst the leave it feeds on, and this brown colour probably serves a similar purpose as the caterpillar looks for a suitable pupation site on a tree branch.

Later today it purged the rest of its waste material. This is a pretty good sign that this guy will pupate tonight.

Another 2 down...brutal.

I lost another 2 caterpillars today, this time from the second cohort (~3rd instar). A spider attacked them between when I checked this morning and when I looked this afternoon.

At least this time I know what happened. I removed the spider and did another head-count. Not including the 2 dead ones I counted 6 from the 2nd cohort - meaning that I must have missed one in a earlier count.

Current inventory:

1st cohort - 5
2nd cohort - 6
Eggs - 5

This is what the eggs look like today:

The darker ont near the top is one day older. It looks like it is about to hatch - maybe even tomorrow.

Revised Husbantry

On my check today I was missing 2 caterpillars...I can't express how frustrated I was. They were 2 of the 3 large caterpillars from the first cohort that I had relegated to the smaller box. There was a small hole in the box that I think was there before, maybe they crawlled out maybe ants or a wasp got to them? You can see the hole near the bottom:

Its still surprizing that there is no trace of them, remember that the smaller cage they were in was inside of my larger screened cage set up. I placed the third one on the live host plant I have in my set-up and went on with my day. A few hours later, I came back to check on the caterpillars. That one little guy had crawled down the plant then along the grass and up the side of the cage! It had traveled roughly 3.2 m and was now hanging on the outer screen of the larger cage.

I put him back on the live plant then geared up for a new set-up for the big guys.

Aside: Earlier tests with larger cuttings have shown me that the branches can survive and even grow if kept in water and sun. Smaller ones dont do well and need to be replaced daily.

I have now taken all the large caterpillars and placed them in seperate tupperware containers with holes in the top. Each has a few sprigs that will need to be replaced daily, but at least they are safe and contained.

4 new eggs

The huge female laid another 4 eggs today, but unfortunately she also died. I was really hoping that she would lay more eggs. Including the egg she laid yesterday she layed 5 eggs. Warm temperatures are necessary to induce female Tiger Swallowtail butterflies to lay eggs so I use a heat lamp over the host plant that I sleeve females with. She ate well this morning, so I think the female probably got tangled in the branches or support structure I have for the mesh sleeve and died of heat stress. I will have to fix this issue so I can prevent future mortalities. Suggestions are welcome (please comment below).

Current Inventory:

• 7 large caterpillars (3 5th instar & 4 <5th instar)
• 7 small caterpillars (between 2-4th instar)
• 5 new eggs

New egg and new caterpillar set up

The HUGE female laid an egg today! This is exciting, hopefully she lays more tomorrow. Here is the egg:

A few of the caterpillars are getting large now and starting to seriously defoliate the live tree I have for the female to lay eggs on.

So I have relegated the three biggest to a smaller cage with fresh clippings. I left the other 3 medium-large caterpillars and the 7 small caterpillars on the live plant under under the heat lamp to help them grow faster (insects grow quicker in warm environments). 

5th instar: full eyespots displayed

Here are some updated shots of the Papilio canadensis caterpillars. They are now getting much larger - and their eyespots are in their full glory!

Below is a rare shot of a caterpillar that recently moulted (i.e., shed its skin). You can see the shedding beside it in the photo. Remember that moulting means that the caterpillar has now passed into the next instar!

HUGE female Papilio canadensis

I caught a huge female Papilio canadensis today. This is the largest Papilio canadensis butterfly I have ever seen. I have never even seen a wingspan this large ever reported. It was so big I started wondering if it was another species. I have her enclosed with Trembling Aspen - hopefully she lays eggs.

Update: A reader contacted me and suggested that this may in fact be a Papilio glaucus butterfly. This was based on the time of year I caught it. In my area we have both species, which I didn't initially realize. It could also be a P. canadensis X P. glaucus hybrid. Apparently it is quite difficulty to visually distinguish the two species (or their hybrids). I have been told that around Ottawa and further north a butterfly in May and June is likely Canadian Swallowtail (Papilio canadensis), and anything later than July 1 is an Eastern (Papilio glaucus). In Kemptville and Oxford Mills though we may be far enough to see first-generation Eastern Swallowtails... I'd be happy to hear any ID tips from readers!

Details:
Sex: Female
Wingspan: 12cm
Body length: 3.3cm (includes head, thorax & abdomen)
Caught July 7 2011 1:00PM by T. Hossie in Kemptville, ON
45°02’52.64’’ N
75°39’33.50’’ W
Elevation: 86m
Notes: Observed feeding on Milkweed (Asclepias syriaca) flowers

Black Swallowtail (Papilio polyxenes) caterpillar

Today a fellow naturalist came across a Black Swallowtail (Papilio polyxenes) caterpillar.

Though still in the Papilio genus, the caterpillars of this species do not have eyespots. Instead they are considered to be aposematic.

Aside: Aposematism is a phenomenon where prey advertize their unpalatability to their potential predators through bright or conspicuous warning colours. Predators learn quickly to avoid consuming prey with colour patterns associated with a toxic or bad tasting meal.

Black Swallowtail caterpillars lay their eggs on a narrow leaved herbaceous dicot called Queen Anne's Lace (Daucus carota), also called Wild Carrot. Most people in Ontario have probably seen this plant:

As you can see, Queen Anne's Lace is a narrow-leaved plant. It has been suggested that prey are likely to evolve aposematism when they live in environments where it is difficult to hide. Prey that can't hide from predators you need something to deter them from attacking, unpalatability is a common solution in nature. Also, there should be a minimal cost to having conspicuous colour patterns for prey living in environments where they can't hide well anyway. There was an amazing paper published in 2007 demonstrating that this seems to explain the evolution of aposematism in Papilio caterpillars very well:

Prudic KL, Oliver JC, Sperling FAH (2007) Signal environment is more important than diet or chemical specialization in the evolution of warning colouration. Proceedings of the National Academy of Sciences 104:19381-19386

The colour pattern of Papilio polyxenes has also been suggested to be cryptic when viewed at a distance, but aposematic when viewed closely. This could give provide an ideal strategy for these caterpillars because some birds may consume these caterpillars despite their unpalatability and some predators may even target aposematic prey when other food resources are low. Also, if predators do need to learn to avoid these prey by eating one, being slightly cryptic could help reduce the number of attacks by naive predators.