By Angela Ten Junior Fisheries Biologist
Welcome to part three of our aquatic macroinvertebrate series. Part one provided a brief intro into the world of macroinvertebrates, while part two discussed some non-insect invertebrates. In this article, let’s take a deep dive into some aquatic insects!
What’s the Coolest part of a Water strider? Their Wings, of Course! Most people don’t think about wings when they think about water striders. Why would they, when they have such funky long legs and can walk on water? But did you know that water striders can change their wings between generations?
Photo credit: Alexander / Flickr
This trait is called flight polymorphism, or the ability for water striders of the same species to have variations in their wings and flight muscles, and it allows them to be super adaptable. In one species, adult striders found in summer have short or absent wings, while striders found in the fall have long wings.
This is because resources are abundant in the summer, so the striders can often live their whole lives in the same area. Therefore, instead of spending energy developing wings, it makes more sense to spend that energy to grow bigger and reproduce prolifically. However, when resources become scarce in the fall, it is more advantageous to have long wings, so the water striders can fly to multiple different habitats to survive. If they had no or reduced wings in the fall, they are more likely to starve or freeze to death.
Water striders with seasonal variation in wing length use day length to determine wing length. When days are long in the summer, striders produce offspring with short or absent wings. But as days grow shorter in the fall, more long-winged water striders are born.
Scuba Divers of the insect World! Although aquatic beetles spend most of their time underwater, they actually breathe air, just like us. Most aquatic air breathers, like dolphins and otters, simply hold their breath while underwater. However, aquatic beetles don’t have lungs, so they can’t hold their breath. Instead, they take a bubble of air underwater with them, and breathe from the bubble—kind of like a little scuba tank!
Some beetles will carry the air bubble under their hard wing casings, called an elytra. Others utilize tiny hairs over their body to hold a super thin layer of breathable air over their entire body. This layer is called a plastron, and it makes the beetles look shimmery and metallic. Even with a scuba tank, humans need to come up to refill their tanks with air. However, a beetle’s air bubble can actually replenish itself underwater. The large surface area of the air bubble allows it to draw oxygen from the surrounding water into itself, partially refilling it. Most beetles still have to come up to replenish their bubbles eventually, but beetles that can maintain a plastron can stay underwater for their entire life. They’re living a scuba diver’s dream!
Nightmare Phantom Midges, and How Their Prey Cleverly Adapts to Them. Phantom midge larvae are named for their ghostly, transparent coloration. While adult phantom midges are harmless, and either eat nectar or nothing at all, their larvae are fierce predators. Their antenna has been modified into a structure resembling a praying mantis’ arms, with long bristles that can unfurl into a basket. These bristles prevent prey from escaping the larvae’s grasp and make phantom midge larvae extremely effective ambush predators.
Phantom midge larvae prey mostly on small invertebrates. One of their common prey items called daphnia has an interesting adaptation that only shows itself in the presence of phantom midge larvae.
Normally, daphnia have a smooth, rounded appearance. However, phantom midge larvae naturally release chemicals called kairomones. When kairomones are detected in the water, daphnia produces offspring with a spine on the back of their neck. These neck spines make it harder for the phantom midge larvae to maintain their grasp on the daphnia, so the daphnia has a higher chance of wriggling away from the larvae’s hold, free to live another day.
Aquatic Insects are the Gift That Just Keeps Giving. There are too many to discuss in just one article, so stay tuned for part four of this series, where we will cover some more aquatic insects. If you have any aquatic insects that you really want us to explore, let us know on our social media channels, Facebook and Instagram!
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