For today’s Friday 5, I’m going to discuss five aquatic insects that suck. No, not that kind of sucking! These are insects that have suction cups, or suction cup-like structures, that allow them to live in their aquatic habitats. Now I don’t know about you, but I find it pretty amazing that there are insects with suction cups on their bodies, so I feel the need to share the love! In no particular order, I present 5 aquatic insects that suck:
Water penny, top view 
Water penny, bottom view 1. Water pennies.
Water pennies are funky insects – and yes, that IS an insect! As adult beetles, most species aren’t that exciting, just nondescript black beetles. But the larvae, pictured here, are bizarre! These insects don’t have suction cups on their bodies like most of the other insects on my list today. Instead, their whole broad, domed shaped bodies work like suction cups! I’ve written about how water penny larvae work before, so I won’t go over it in detail again here. However, if you think of the little plastic suction cups you use to stick things onto windows, you’ll have a pretty good idea of how the suction works. You’ll find these living on the tops of rocks in cold, fast flowing streams.
Net-winged midge larvae, top 
Net-winged midge larvae, bottom. The dark, round discs are the suction cups. 2. Net-winged midges.
Ah, blepharicerids. I can remember the first moment I found one of these in a stream. I nearly yelled out in utter joy! It’s one thing to see pictures in a book and quite another to find hundreds of them all over rocks in a stream. These fly larvae are truly amazing. They’re bizarrely shaped, even by insect standards, with constrictions along the length of the body. Each constricted section also contains a suction cup. Like the water pennies, they live right out on top of rocks in cold, fast flowing streams, so they’re constantly being slammed with water as it flows downstream. The suction cups keep them from being swept away! (If you think the larvae of these flies are interesting to look at, I highly recommend that you take a look at the pupae. Weird!)
Predaceous diving beetle (Thermonectus nigrofasciatus) 
Predaceous diving beetle foreleg. The suction pad is made up of several individual suction cups. 3. Predaceous diving beetles.
These are the only adult insects I know of that have suction cups. And, they don’t use their suction cups to prevent their washing downstream like most aquatic insects with suction cups. Any idea what they might be used for? Hint: only the males have them. These suction cups are used during mating! Predaceous diving beetles are extremely well adapted for swimming and exhibit very smooth, domed bodies that allow them to move through the water with surprising grace. If you’ve ever tried to pick one up with forceps, you know how slippery these little buggers are! This causes problems when a slippery dome-shaped male wants to climb onto his slippery domed-shape mate’s back and get down to business. So, they evolved suction cups on their forelegs! You can see them there in the photo – lots of little suction cups making up a big suction pad. The male presses the suction pad onto the female’s back and is able to hold on long enough to mate. Pretty neat, eh?
Rhithrogena impersonata. Photo from http://www.troutnut.com/specimen/482.
Rhithrogena impersonata, bottom. Photo from http://www.troutnut.com/specimen/482. 4. March brown mayflies.
Mayflies in the genus Rhithrogena (family: Heptageniidae) are rather similar to the water pennies in that they do not have true suction cups. Instead, they have flat bodies and their abdomens are ringed by broad, flat gills. The space between the gills works like a suction cup and keeps these mayflies attached to the rocks on which they live in streams. While these nymphs are not dome shaped like the water penny larvae, their suction cup works in a similar manner.
Leech. Leech sucker is inset. 5. Leeches.
Leeches are not insects. In fact, they’re not even arthropods! However, they are aquatic and they definitely have suction cups, so I’m including them in my list. Leeches use their suction cups to grab the substrate or to hold onto their prey as they suck their fluids. I also personally think they add to the overall distasteful appearance of these animals. I mean, what’s not to love about an animal that uses a sucker at one end to attach to you and a sucker at the other end to suck your blood? :) (Okay, I’ll admit that I do actually like leeches. Ever seen one swim? It’s both horrifying and mesmerizing and I can’t tear my eyes away!)
Don’t know what I’ll do next week! I have a long list of ideas, so it will depend on my mood when I sit down to write. Maybe something Christmasy!
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