Field Trip: Tommy Thompson Park

On Saturday, Sept 12, 2026, five survey members spent the day in Tommy Thompson Park in search of caterpillars that are uncommon or not known to be present in High Park. This was the survey’s first-ever field trip outside the borders of High Park.

The morning started off with some familiar species that we see regularly in High Park: Hickory Tussock Moths, Poison Ivy Leafminer Moths, and Fall Webworm Moths. We soon came across one of our target species, the Finned-willow Prominent (shown below), still within sight of the visitor pavilion! Along this short stretch of road, we ended up finding five of this attractive species.

Finned-willow Prominent

The next highlight of the day was a species we only occasionally see in High Park: The Asteroid. This racing-striped caterpillar is always a crowd-pleaser. While we didn’t find any late instar Asteroids, the three middle instars we saw, although not as boldly patterned, still gave us most of the experience.

The Asteroid

Just down the road from The Asteroids, we found our second target species for the day - a small Smeared Dagger resting on a dogwood leaf. Since it was an earlier instar, we didn’t get to see the more impressive patterning of the more mature larvae - but it was still a worthwhile sighting.

Smeared Dagger

Upon coming to a clearing along an overgrown path, one of our group spotted a Mourning Cloak caterpillar about to pupate on a large stone. A Siberian elm (a host plant for the species) was just behind the rock, so we checked there for more - only to find a few caterpillars of a different species: two Question Marks! This species is known for having what look like “horns” on the top of their heads, but one was missing this feature.

Question Mark

While most of the group was observing and photographing the Question Marks, another member of our team spotted our last target species for the day: a pair of Spotted Datanas! In the excitement of the discovery, we almost didn’t notice a larger group of about twenty individuals just a few small branches away. One of the distinguishing features of this species is a pair of dark, spiny “horns” on the top of its head, but one of the Question Marks we found was lacking these “horns” for some reason. Fortunately, there were other features that helped us to identify it.

Spotted Datana

On our walk out of the park, we came across a leaf-construction on staghorn sumac that housed a species never before reported in Toronto: Striped Sumac Leafroller (Sciota subfuscella).

Striped Sumac Leafroller

Great weather, great caterpillars, and great company made it a very enjoyable field trip. In all, we saw 542 caterpillars of 29 species.

Here is the complete list of species we found that day:

• Banded Tussock Moth
• Blackberry Looper
• Camouflaged Looper
• Carrot Seed Moth
• Common Pug
• Fall Webworm
• Finned-willow Prominent
• Hickory tussock
• Large Gray Dagger
• Milkweed Tussock Moth
• Monarch Butterfly
• Mourning Cloak
• Poison Ivy Leafminer
• Polyphemus Moth
• Purple Carrot-seed Moth
• Question Mark
• Salt Marsh Moth
• Scarce Straw Pearl
• Silver-spotted Skipper
• Smeared Dagger
• Spotted Datana Moth
• Striped Sumac Leafroller
• Sumac Leaf Blotch Miner Moth
• The Asteroid
• White-marked Tussock Moth
• Willow Leafcone Caterpillar Moth
• Woolly Bear
• Yellow Bear
• Viceroy/White Admiral/Red-spotted Purple (early instar)