Recommendations for a Scale to Weigh Insects

I’m looking for a crowd-sourced recommendation for a scale to weigh insects. This past summer, we carried out a successful pilot season of capturing insects in pitfall traps up in the spruce-fir zone (elevation ~1230 m) here in Vermont. This sampling occurred on (and in conjunction with) long-term avian monitoring plots. I’d like to assess the dry mass of the inverts that we captured so that it may be included as a covariate in my models predicting avian abundance at those locations. Most of the captures were of ground beetles (and other beetles) and slugs, but there’s also some ants, hoverflies, Muscoid flies, and spiders in there. I’m thinking that I need a 0.01 g sensitive scale (or even more sensitive?), but wow–the variation in price of such scales ranges from <$100 to $5000. Has someone had success with a particular brand/model/price point of scale for similar purposes? Thanks Everyone!

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If you’re looking for precision, I’d recommend spending at least $100 on a laboratory scale. Quality brands can be purchased secondhand for cheaper than new price, I personally would go with Mettler Toledo as they have proven to be the most reliable manufacturer of precision lab scales. I’ve used some ancient scales from them and with calibration they were still very serviceable.

EDIT: I should also mention, I have tried multiple scales from Amazon and all of them have been terrible. I bought them for weighing cooking ingredients and they weren’t even useable for that.

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What I would do in your situation was go to Google Scholar, search for papers that also needed dry weights for insects, and see what scale they used. Anything that hasn’t been tested for this purpose is unlikely to be as precise as you need. The dry weight of a typical Vermont worker ant is likely to be something like 1mg or less (depending on the species) so precision of 10mg (0.01 g) isn’t going to do you much good.

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I weighed some acalyptrate flies in my PhD lab, and I used a microbalance that went down to the microgram, although I found the last digit was hard to measure reliably. I weighed them to the nearest 0.01 mg. My flies were about 2 mm long and the dry masses were in the 0.15 to 0.40 mg range. Hopefully that helps give an indication of the precision you may want! Unfortunately the scale predated me, so I have no idea how much it cost (and I no longer have access to it to find out the model).

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Oh, definitely milligram-microgram precision if you’re measuring the weights of individual insects. Not sure if you plan to measure individual organisms or just total mass of everything you find.

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Yeah, it isn’t clear whether you want individual insects or groups? Individual insects you will need 5 decimal places (gms) (or more for small ants, etc.). And then last decimal will be shaky. I could watch the dry ants I massed for my PhD gain weight as they reabsorbed humidity from the air and the balance readings went up and learned I had to control that. The scale I used for the individual insects (in Jim Marden’s lab) cost $1000’s

Massing them in a group might work better and definitely require less pricey equipment. I would suggest figuring out your avg mass that you want to measure, and then getting something precise to a decimal lower. Then you can feel fairly confident you’ve gotten a meaningful measurement.

I’ve gotten some cheaper balances on Amazon that were advertised as accurate to 0.01 gm that we validated against nice balances in the lab and verified that they read to within 0.01 gms of what the “real” balance said. I’ve also seen ones that were awful. If you do get a cheaper one, I would definitely recommend taking that validation step with a nice balance and making sure that they one you get can be calibrated with a known mass weight.

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Good point. I thought the goal was to measure individuals, but if you have a pile of 1000 and just want a total or average, that certainly changes things. That said, my experience with pitfall trapping is that you don’t get thousands, you get a few.

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Excellent, thank you. Yes, I’m interested in precision (i.e., repeatability), but also accuracy. I found a Mettler Toledo for ~$500. Thanks for the tip about cheap Amazon scales. I interpret your comment as a vote to purchase based on the brand name. Got it. It’s confusing to me that the even within a brand, there’s a dozen scales that all appear to do much the same thing with the same functions, but vary in price. In the case of Mettler Toledo the price for a 0.01 g sensitive scale ranges from $500 to $7000 that I found online.

For sure, and I’ve read ~dozen papers that mentioned the particular scale. Without exception they were all scales in the +$1000 dollar range, but that’s probably a reflection of what they have available vs. what was actually needed. If I was still at the university, for example, I’d have just gone next door to the bio-chem lab and used their incredible scale set up. But I bet I can achieve my goal without spending 10K (which I don’t have). :grinning: Completely agree that measuring individual ants is out of the question…and would not be informative for my purposes.

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Right on. My primary goal is to measure dry biomass of the entire trap contents as a proxy of food availability; the work that we’ve published on avian diets up there (e.g., for Bicknell’s Thrush) documented consumption of prey items from dozens of invertebrate families. But it would also be great to measure dry mass at the invertebrate family level (or Order level). I’d say that our trap contents (left out for a week) typically consisted of (very approximately) 10 ground beetles, 4 slugs, 6-12 spiders, and maybe 10 other insects.

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Check among your university connections to see whether an interested researcher will let you come into his/her lab. Check profiles among your local iNat participants, and ask nicely.
Failing the free option, don’t buy a cheap balance! I have a lifetime of laboratory experience, and I doubt that any $1000 scale will have the accuracy that you need.
Universities often auction off unused lab equipment from time to time. And there are liquidation companies that sell used equipment. – but usually it’s “buyer beware”. If you go this route, make sure there’s a guarantee that the equipment is in working condition. You’d have to be very lucky, because I can’t imagine why any researcher would dispose of a working balance.
You could consider RENTING the microbalance that you need. There are a good many lab equipment rental companies (a quickie DuckDuckGo search turned up several).

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I agree. Even if you are no longer at a university, it probably wouldn’t be hard to talk a professor at one into letting you use the scale a few times.

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Beware that most scales which advertise milligram precision can’t accurately measure weights less than 100 milligrams. Sadly, you really do need to buy the expensive scales to get small weight precision.

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Thank you all for the hard reality check. I value all of these comments and the time y’all spent thinking about them. I was hoping someone might chime in with a, “Well I used a $200 model Y from company X for a similar project, and I regularly checked the scale against a 1 g calibration weight, and the results were consistently ± 0.05 g from true.” Sounds like I need to spend much more money that I had imagined if I want the ability to weigh trap contents defensibly. Well, I’m still an Adjunct at U of Vermont, so I’ll reach out to colleagues in our program about borrowing equipment. Hopefully someone will take pity on me. I did not know that you could rent lab equipment(!), and I got a few quotes from here and here. With the minimum rental period looks like it would cost ~$400 to rent a 0.001 g scale. I could always fall back on published length–mass regressions for invertebrate Orders (e.g., here and here).

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I don’t have experience using scales for this yet, but agree it would probably require an expensive scale for precise insect weight measurements. Probably something used in chemistry or another area of science/medicine, vs. most ordinary store brands. For anyone indicating the weights they measure in their observations (by writing them, or using/creating a Field to show them), it’s probably also ideal to distinguish if the weight was when living or originally collected for specimens, vs. if it were later on (if living weight differs from specimen weight, which I assume).

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