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ramé-hart Newsletter

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October 2021

What can we learn from a sewer fly?
The common sewer fly (aka drain fly, sink fly, moth fly, Psychodidae) is a truly annoying insect. If you spend any amount of time around sewers, drains, and sinks (I try not to), you may see these winged bugs buzzing about. While common house flies can carry diseases, sewer flies typically do not - if that's any consolation.

If you were to examine the behavior and habits of the sewer fly, you would observe that they love wet environments. In fact, their ideal home is in your toilet or laundry room sink. They feed off nutrients found in slime that accumulates in drain fixtures. And while they are generally pretty mellow lazy creatures, they do show a spark of life when the toilet flushes or a faucet is opened. However, their ability to evade being flushed down the drain lies not so much in their keen flying skills and sharp reaction time, but rather in their furry bodies which are coated with thousands of minute hairs that form a superhydrophobic hierarchal structure that is resistant to wetting. In short, you could say they are equipped with a water-repelling exterior.

Similar types of surfaces are omnipresent in nature. In the past, we've discussed water striders1, the lotus leaf, gecko feet, moth eyes, and the Namid Desert Beetle.2 Nature has a special way of protecting critical living surfaces from water using a combination of microscopic and nanoscopic structures forming a hierarchal structure.

What's unique about the sewer fly is the wide range of droplet sizes that it can evade due to its anti-wetting exterior - everything from large drops down to microscopic droplets and even mist. Researchers found that there are three different classes of hair on the sewer fly.3 The water contact angle on the wings, for example, with larger droplets is close to 180° which confirms the Cassie state. Additionally, the roll off angle is very low for these drops. Even when a sewer fly is hit with multiple water drops in succession, their hairy little body and wings repel the drops and alert it to the danger - giving it time to flee. However, when the incoming droplets are not water, the insect has a harder time recovering and the water repellant exterior loses its effectiveness to non-water droplets. 

In the case of mist, the drops become so small that they fall down in between the hairs. Tiny droplets form on the edge of the wings away from the body. With a flap of the wings, the drops are dispersed and with occasional flight, the sewer fly is able to stay dry. Interestingly, it's in these misty environments that the fly is most likely to urinate by extending a conical spike, ejecting the urine droplet with sufficient velocity to avoid self-wetting, and then the conical spike retracts.

The sewer fly's survival depends on its superhydrophobic body which is made up a hierarchal structure similar to other structures found in nature. The particular design found in the sewer fly appears to be optimized for a wide variety of droplet sizes, from rain drops down to mist. Even submerged, the tiny hairs form a layer of air between the insect's body and the surrounding water allowing it to survive underwater for hours.

By better understanding the sewer fly's morphology, scientists can better design manmade superhydrophobic structures that mimic those found in nature


1 See our December 2015 Newsletter.
2 See our December 2019 Newsletter.
3 Speirs, N.B., Mahadik, G.A. & Thoroddsen, S.T. How drain flies manage to almost never get washed away. Sci Rep 10, 17829 (2020). https://doi.org/10.1038/s41598-020-73583-2

The New Manual Syringe
This month we are excited to introduce our new Manual Syringe p/n 100-10-52. One of the most critical steps in measuring contact angle is the formation of a sessile drop. For years we have offered both an automated approach using our Automated Dispensing System as well as a manual method using a microsyringe assembly. The company that made our microsyringe product, Gilmont, has gone out of business and thus these microsyringe assemblies and the replacement glass barrels are no longer available.

After exhaustive testing, we've settled on a worthy replacement. While our new Manual Syringe offers the same level of precision dispensing, it also offers (3) competitive advantages. First, it's less costly. You can purchase (3) Manual Syringes for the same price as the retired microsyringe. Second, there are only two parts, the glass barrel with male Luer connection and the plunger with a PTFE tip. This makes it easy to clean and maintain with fewer parts that can get lost or broken. For operational instructions, see this document. Third, the Luer connection is a locking type which keeps the needle from falling off and is compatible with every type of dispensing needle we offer - straight, inverted, PTFE, etc.

ramé-hart 250 Manual Syringe p/n 100-10-52

In order to use the new Manual Syringe with an existing ramé-hart instrument, you will need a Syringe Adapter p/n 100-10-51. To get started with the Manual Syringe, you may be interested in our Set of Spares for Manual Dispensing p/n 100-SPARES-21 which includes (2) Manual Syringes, (1) Syringe Adapter, (4) 22g Straight Needles, and (10) 22g Disposable Needles.

The feedback from our customers who have tried our new Manual Syringe has been positive. We invite you to consider the Manual Syringe when your microsyringe wears out or expires. All of our manual dispensing products can be found and ordered on this page: https://www.ramehart.us/manual-dispensing/.


Carl Clegg
Director of Sales
Phone 973-448-0305
Contact us


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