THE DUNG BEETLE: Cleaning up bullshit one idea at a time. This Week: “Absence of evidence is not evidence of absence”

We hear this all too often, but it is completely wrong. Of course it’s fun to say, mostly for two reasons: 1) it makes the speaker seem open-minded and wise, superior to the surrounding listeners; and 2) because it does that fun word flippy thing (which I’m sure has a specific name well known to literature teachers and poets).

Simple caveat: “Absence of evidence is not PROOF of absence” is absolutely correct. I think this is what most people mean when they use the other phrase.

Second caveat: An “argument from ignorance” is different beast all together. I’m interested in situations where good observations have been made, tests have been run, etc.

“Absence of evidence is not evidence of absence” —let’s state that a different way. Failure to find evidence for thing X cannot be used as evidence that thing X doesn’t exist. Let’s apply this to a real word situation and see how it turns out.

Is there an elephant on campus? We have no sighting’s, no prints, no poo, no damage to vegetation, no noise. If “absence of evidence is not evidence of absence” then how do we comment on the probability of the presence of an elephant on campus? In fact, all we have is “absence of evidence”.

Now let’s try the unicorn. Do unicorns exist? Should I be scared of a goring when walking home late at night? Should we put aside some unicorn habitat so they can run free and mate and have baby unicorns? There is an absence of evidence for a real unicorn, so again, how do we go about gathering evidence of its absence?

All this does not mean, however, that later evidence may come to light and we must refine our ideas about the universe. That is an understood aspect of the Thing we call Science. But as it stands, if we go looking, and don’t find anything, then yes, we can use that as evidence (but not proof) that what we’re looking for isn’t out there.


Extension Pete in: The Case of the Frenzied Fleas

A knock at the door, an approaching smile, the door opens.

Says the man on the stoop: “Hello, I’m Extension Pete,” dramatic pause, “Entomologist Detective!”

“I know, I called you,” says an engaging young mother holding a wide-eyed baby on her hip.

“Good.” Not at all deflated that she wasn’t overwhelmed by his appellation, he continues, “What seems to be the problem?”

She invites him in with the wave of her hand into an empty house full of boxes. “We just closed on the house last week and started moving in. A couple days ago the baby and I moved some boxes in, and when we got back to the old house she had some fleas on her. It was weird, I caught them with tape, and then, I don’t know, there’s just so much going on, I forget about it. But then it happened again yesterday!”

The excited young man is snooping about the house, peering in corners and closets, gently probes a box marked FRAGILE! with his boot, hears some tinkling, and retreats quickly.

Eye contact: “Any pets at your other home? They might have picked something up from the neighbors.”

“No pets. No cats or dogs,” shake of the head, “We’re planning on getting some though; children that grow up with two or more pets tend to have fewer allergies,” coos at baby.

Authoritatively, “You should get a llama. They’re the Gentle Camel.” Resuming inquisition, “Are there any pets here, in the house or maybe strays that live under the house, in the neighborhood?”

“No, no pets in the house. The last owners had a cat, but they’ve been gone for months. I haven’t seen any strays in the neighborhood. But the baby hasn’t been outside. I carry her from the car to here and then put her in her chair or let her crawl around.”

Lifts gaze from a box with the overly Dickensian label “Christmas Past” and shifts attention back to mother and child. “Whereabouts has the bundle of joy been crawling?”

Mother leads the way, pointing from spot to spot in various rooms, comments on cute things child did while in each spot: had fun in Kitchen slapping linoleum and listening to resulting sound; frightened and intrigued by border between linoleum and tile of utility room; overcame previously mentioned fear of tile and entered utility room to gain safety of mother’s ankle; use of traction provided by carpet in back bedroom to produce sudden bouts of speed crawling.

The tour ends. A grandiose statement from the young man: “I believe I have solved the mystery. But first we should celebrate with some homemade root beer. I shall return.” Exit Extension Pete.

Return, doorbell, greetings, bags on counter in kitchen, root beer extract, sugar, dry ice, mother sets about finding/cleaning a pitcher. Root beer is made, chitchat, baby is entranced by vapor. After the glasses are drained, “Well, that should be enough time, let’s go check,” and our sleuth leads the way to the back bedroom, opens door, peers in.

Scattered over the floor, a few remaining chunks of dry ice sublimate away quietly. Several glue traps rest sticky side up on the floor, each bespeckled with fleas. The good mother’s expression is translated as, “What sorcery is this?!”.

The reveal: “Fleas has a life cycle similar to the butterfly. There’s an egg, then a larva—a squirmy, wormy thing like a caterpillar or grub.” Eye contact to make sure she was following, hand gestures for emphasis. “Once the larva gets big enough it spins a cocoon and becomes a pupa, just like a butterfly or moth. Eventually the pupa becomes an adult flea. But fleas are professional parasites; they aren’t at all interested in being adults unless there is something to eat. If there is no physical movement, heat, or carbon dioxide an adult flea can hang out in the cocoon for more than three months. These fleas are leftovers from the previous owner’s cat. Once everyone moved out, they just sat tight waiting for someone else to come along.

“Fleas are in carpets, rugs, or cracks against the wall, not on tile or linoleum. The baby provided all the stimuli needed to wake the fleas up, and this is the only place the baby has been where some could be hiding out. Voilà: fleas on a baby. The carbon dioxide from the dry ice woke the rest up. Mystery solved and confirmed.” Big grin.

“That’s amazing!” Retreating from room entrance, “How do we get rid of them?”.

“Well there are any number of chemicals, you could steam clean the carpet, you could pull it up and put down hardwood. Probably you don’t have to worry about immature fleas, those have either died or become adults. That should make control easier.”

“You’re amazing Extension Pete.”

“I know I am.”

“How can I ever repay you?”

“I need no payment. Just know that wherever there’s an entomological mystery I’ll be there, for I am…” dramatic pause, “Extension Pete: Entomologist Detective!”


Curatorial Perambulations I

What is the Best “Collecting” Strategy for an Arthropod Museum?

A species consists of a population made up of individuals. Much information about a species can be found in one specimen (especially morphology). However, information about a population (=variation) requires many specimens that exhibit the ranges of morphological and genetic variation, distribution, phenology, etc.

Considering that resources are limited, what’s a curator to do? Maximize number of species for morphological vouchers, or maximize specimens of a particular species to create a robust representation of the population?

Short answer:

Do both! Get pretty much everything.

Long answer 1:

When trying to identify an unknown, even a single identified specimen can be incredibly helpful. Endeavors that benefit greatly from even a single specimen include classes, key creation, field guides, voucher collections (physical and photographic), checklists, etc. So maximizing species has benefits.

Most arthropod collections have geographic and taxonomic strengths/biases (see this brilliant paper: Ferro and Flick 2015), that is, they are often dominated by local specimens. (How overlap between “museum range” and species range affects our understanding of a species’ distribution is an interesting idea, but not for this essay.) Retaining a large number of specimens of local species may add greatly to the overall understanding of a species’ population, after all, who else should be collecting these beasts? So maximizing specimens of species has benefits.

Perhaps the best way to answer the question is to consider its inverse: What shouldn’t a curator do? Which specimens are of the least value?

(Generally speaking!) The specimen that carries the most morphological information is the singleton. Every other specimen of that species provides less and less morphological information, they only contribute information on variation. The specimens that provide the most population information are the outliers (geographic, temporal, etc.) because they help define extremes. Therefore, the specimens that carry the least information represent a species, life stage, time, AND place that is already represented by another specimen in the collection.

Specimens of the same species collected at the same time and place are often called a “series”, usually defined as 5, 10, or 20 individuals. A series is an important tool for the arthropod collection. It assures that plenty specimens are collected to account for breakage, individual variation, sexes, cryptic species, and abnormal abundance of rare species. But a series can go too far (this is less true for alcoholic preservation where 50 specimens may take up no more room than one). Maybe pointing 100+ ptillids from a single litter sample, or 1000+ throscids from an emergence study is unnecessary (the author is guilty of both).

Perhaps the best strategy for a collection manager is to maximize both: 1) the number of species; AND 2) specimens of a particular species, but work to keep redundancy of those specimens below a maximum threshold, and therefore not squander resources on “lower value” specimens.

Long Answer 2:

Not long ago museums had exclusive (more or less) resources such as museum workers, specimens, literature, etc. A user had to travel to the collection to use the resource. And, even though it seems obvious, the collection either had the resource or it didn’t (getting the resource, even a paper, took time and money).

Digitization of information (and all that that entails) has changed the landscape of cost and access to materials. For example, to peruse The Canadian Entomologist a reader no longer needs to travel to a museum or library—and to possess The Canadian Entomologist a collection no longer needs to have actual copies. It makes little sense to purchase Volume 1 (1869) when it is available for free online. (I’m not saying don’t expand your library, just make wise decisions.)

For collections a “resource spectrum” has developed. One end consists of resources that are fully digitizeable and can be created, duplicated, and/or passed around with ease including specimen label data. The other end consists of those things which cannot be digitized: the smell of naphthalene, a rousing debate over lunch about whether termites are cockroaches, and above all, physical specimens.

Digital “shadows” of specimens can be created, label data, photographs, DNA, etc., but an actual specimen cannot. The cost of obtaining specimens will almost certainly increase with time. Paperwork associated with obtaining, transporting, depositing, and holding a specimen has increased greatly. (These delusional handicaps placed on researchers and institutions are an important and too often overlooked cost/impediment to collections and research, but that’s a topic for a different essay.) The point is, from the standpoint of a multigenerational collection, now is probably the best (cheapest) time to obtain specimens (and other non-digitizeable resources).

As was mentioned above, even a single specimen provides a lot of information about a species. Additionally, a collection either has a specimen, or it doesn’t. Borrowing a specimen from another institution costs time and money. (Enormous amounts compared the first edition of The Canadian Entomologist. Cost to download the first edition of The Canadian Entomologist = $0.00. Cost to mail a package = $10.00. Therefore mailing a specimen is infinity percent more costly than downloading a free paper. That’s just math.)

In this scenario, increasing species diversity is the best strategy for small or extremely resource-limited collections. Population level information, such as distribution, phenology, etc. can be supplemented through other online specimen-level databases (but beware! see paper cited above).

My overall proposal is that museums should ACTIVELY work to increase their taxonomic holdings AND actively work to help increase the taxonomic holdings of other museums.

Now is the cheapest time (cost will only increase in the future), and actual specimens have clearly emerged as the highest “value” artifacts in a collection (because they are non-digitizeable). It is not inappropriate to imagine a future where all midsized and larger museums have one or more representatives of every order or family of insect, arachnid, etc. known on the continent, or even representatives of every genus (or species of the smaller orders: the 13 smallest orders in NA north of Mexico have a total of 511 spp. Five specimens of each species = 2,555 specimens, or 0.2555% of a million specimen collection.)

Something to mull over…