While scanning the water below the bridge at the Sugarbush Trail, a large black and white insect flying by caught my attention. I thought it was a moth at first, but a closer examination revealed it to be something quite different. It looked like the fishflies I’d seen mothing with Diane Lepage in summers long past, but I’ve never seen any that had white spots on the wings.
A review of Bugguide.net indicates that it is one of the dark fishflies of the genus Nigronia, which belongs to the Family Corydalidae (the dobsonflies and fishflies). There are only two species in this genus, and both are dark with white markings on the wings. The larvae are aquatic, which means adults are most often found near small rivers or clear, narrow streams. Like other members of this family, the adults have a short flight period and either do not feed, or feed on small amounts of nectar and fruit juices. The larvae are predators, and eat aquatic insects, tadpoles, and small fish. While the adults are chiefly diurnal, they are also attracted to lights after dark.
A small Hobomok Skipper was also seen fluttering in the area, and landed briefly on the wet soil where it used its proboscis to obtain moisture from the ground.
We headed into the woods, and I was surprised to see the vegetation overrun with small blue and yellow caterpillars. I think they were the most abundant organism of our outing, and in some places there was hardly a plant that didn’t have any crawling on them. The yellow “footprints” running down the back identify this as a Forest Tent Moth caterpillar, which is similar in appearance to the Eastern Tent Moth caterpillar. Both of these caterpillars are considered pests, though only the Eastern Tent caterpillars live in colonies which create large, silky tent-like cocoons in trees to protect them from the summer heat and rainy weather. Both species pupate in individual cocoons in sheltered areas.
Forest Tent caterpillars feed on broad-leaved trees such as trembling aspen, oak, ash, maple and white birch. The caterpillars can cause extensive defoliation during widespread outbreaks, which usually occur in the boreal forest at intervals of 7 to 11 years; each outbreak can last 3 to 6 years. Trees that undergo heavy defoliation in several consecutive years become weakened and may suffer from a reduction in growth or considerable branch and twig mortality. They also tend to become more susceptible to stresses such as drought or other pests. The number of trees damaged by these outbreaks can be enormous: previous outbreaks have resulted in damage covering areas varying in size from 150,000 hectares in 2009 to 14.3 million hectares in 2001.
We found the caterpillars throughout the vegetation right up to the water. In some cases they were crawling on the rocks right at the water’s edge, or falling into the water right out of the trees. Those that fell into the water didn’t last long; we saw a couple floating on the surface that were immediately snapped up by hungry fish.
Chris found a couple of Sedge Sprites lurking in the vegetation; one of our smallest damselflies, they can be difficult to see (especially since they are green).
An Arctic Skipper sunning itself was our only other butterfly of the day:
Although the Forest Tent caterpillars were the most abundant species of our visit, the jewelwings along Chelsea Creek were a close second. The only ones that I noticed there were River Jewelwings; their wings are slimmer than those of the Ebony Jewelwing, and males have noticeable dark tips to the wings. Jewelwings have a habit of opening and then snapping their wings shut while perching, and I caught one in the act. Perhaps he was trying to impress the female on the left.
This male was perching close to one of the caterpillars.
After leaving the stream we returned to the main path in the woods where I found this Aurora Damsel perching on a sunny leaf. These damselflies can be mistaken for spreadwings due to their habit of perching with their wings out at an angle, but spreadwings generally have a narrow black or metallic green abdomen without any blue rings running down the length. Their black and blue colouration is similar to the bluets, but Aurora Damsels can be distinguished from them by the single black patch on top of thorax instead of shoulder stripes – this black patch is distinctive in that it has wavy edges. Males also have a bright yellow patch on the lower side of the thorax.
We found more jewelwings at the Dunlop Picnic area, and these ones were mostly Ebony Jewelwings. They have a much broader wing than the River Jewelwing, which is useful for telling the females apart. Males have a jet black wing.
Although Ebony Jewelwings are usually found along slow-moving streams and small rivers in forests or heavily wooded areas, I’ve often seen them in forest clearings well away from the water. These damselflies like to perch on low shrubbery in sunlit openings, and when they fly, they look like large black butterflies.
The only other damselfly species we found were a few Aurora Damsels in the vegetation near the stream. Here the wavy black patch on top of the thorax is visible. Unlike bluets, which have black eyes with blue eyespots, Aurora Damsels have blue eyes.
The most interesting insect we saw at Dunlop wasn’t an ode, but a crane fly – we saw a couple of these huge flies resting on the rocks in the stream just like some of the jewelwings. Although their bodies were small, their legs were about three times the length of their body. I was careful not to step on any while trying to catch the spiketails flying up and down the stream.
Our trip to Gatineau Park was quite successful – the weather was great, the scenery was gorgeous, and there were lots of fantastic odes and other insects. As mentioned in my previous post, we found representatives of five dragonfly families, as well as two of the three damselfly families (all we needed was a spreadwing). The variety of odonates in Gatineau Park is one of the best things the park has to offer, in my humble opinion, and a visit there in June or July is a must for any dragon-hunter.
Thank you so much for id’ing the dark fishfly! I watched lots of them this spring along an Oakville creek but didn’t know what they were.
Never thought tent caterpillars could look so pretty 🙂
That was an unreal year for those caterpillars. They were so plentiful you could hear their poo falling like gentle rain.