Sweeping Into Action

This week we deployed a sampling team of 5 to set up 3 sites for standardized sampling at rare Charitable Research Reserve in Cambridge. Four colleagues and I set out early Monday morning to get started on our days’ work. I was eager to get back out to the field and set up some traps. For a few of our crew members it was their first time preparing the array of traps for our standardized sampling.

This is a picture of me taking some GPS coordinates at one of our sampling sites. This site was located in a hard wood forest, dominated by maple trees
This is a picture of me taking some GPS coordinates at one of our sampling sites. This site was located in a hard wood forest, dominated by maple trees

So there were great learning opportunities and I really enjoyed showing some of what I had learned last summer aboard the BIObus. By the end of the day everyone had learned our routine and we were all working efficiently together. I can confidently say that everyone was enjoying themselves on our first day out as a big group, we had good weather and everything went smoothly.

Part of standardized sampling is sweep netting. We use a butterfly nets to “sweep” through the vegetation close to the ground. This technique targets both flying and sedentary insects found on vegetation such as caterpillars and sawfly larvae (order: Lepidoptera and Hymenoptera). As we swing our nets through vegetation it knocks the arthropods into our nets while the constant sweeping motion keeps them trapped inside at that back of the net. This affords us the convenience of insects flying right into the path of our nets as we disturb them from their cryptic hiding places. When sweeping sites we try to encompass the entire site, sweeping through all vegetation types in efforts to capture a greater diversity.

Here again at our hardwood forest site, Dan (left) and Shannon (right) are sweeping the understory for insects. Sweep netting is part of our standardized sampling protocol, where we net insects for 5 minutes
Here again at our hardwood forest site, Dan (left) and Shannon (right) are sweeping the understory for insects. Sweep netting is part of our standardized sampling protocol, where we net insects for 5 minutes

Many insects and arthropods are host specific or are associated with only a small hand full of plants. If I were to sweep through long green grass I would expect the see a lot of treehoppers (Membracidae), planthoppers (Fulgoroidea), and leafhoppers (Cicadellidae). This was all to true when we swept two of our sampling sites that are dominated by grasses. The abundance of these hemipterans, true bugs, was astounding. With our aspirators we were literally removing handfuls of insects from our nets. These sweeps provided the largest samples I have ever taken with a sweep net. Our last site is located in a hard wood forest dominated by maples. In comparison to the grass sites I would not expect to find the same abundance of hoppers, rather there is commonly a greater abundance of flies. The sweeps of the forest site produced just that. We netted a huge mass of mosquitos and crane flies. In retrospect all of the sweeps this far at Rare have proved to be highly productive and have surpassed in biomass anything in sweep nets that I have done previously.

After we sweep for 5 minutes he have to empty the insects and other arthropods of our nets. From left to right, you can see me aspirating along with Josh who has his entire head in the net to get better access at the insects deep in his net, and Dan is preparing to empty the insects he has aspirated from his net
After we sweep for 5 minutes he have to empty the insects and other arthropods of our nets. From left to right, you can see me aspirating along with Josh who has his entire head in the net to get better access at the insects deep in his net, and Dan is preparing to empty the insects he has aspirated from his net

As mentioned above we use aspirators to collect the arthropods from inside of our nets. An aspirator allows you to collect small insects with ease in comparison to your fingers or forceps. When aspirating you are actually creating a vacuum by gently inhaling on a hose that’s attached to a glass vial, where by the insects gets sucked up directly into the holding vial. Luckily, there is a fine mesh layer preventing the insects from entering your mouth. I am aspirating in the third picture, you can see the tube that I use in my mouth to create the sucking action required to capture the netted insects. Josh, in the middle of the same picture is employing a classic technique. He is also aspirating his sweep net but he is doing so with his head completely inside the net. This helps to prevent the flying insects caught from escaping while we are aspirating. Beside Josh is Dan, who is inspecting the container he has filled with his aspirator, possibly in awe like I was from the massive abundance of arthropods caught.

-Nate

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