Why are some animals so hard to ID and some so easy?

Why are some/most flies, skippers (Hesperiidae), worms and spiders SO hard to identify without fiddling with you-know-whats (you know, GENITALS :neutral_face: :unamused:) and some birds and mammals so distinct even on the generic level? Why can’t I tell the difference from Branded swifts (Pelopidas) without genital examination, and why is the grey wolf SO distinctive even within its own genus??? WHY CAN’T I DISTINGUISH BEETLES WITHOUT EVEN MORE FIDDLING AND WHY CAN I BE SURE THAT SOMETHING’S A TINY GRASS BLUE??? ARRRRGH! :confused: :scream: :scream: :scream: :flushed: :flushed: :flushed: Any help?

Is there any evolutionary reason that teeny-tiny bugs are so hard to give species ID’s to and some mammals are so distinct even on the closest-living-relative scale (except monotypes)?

That’s how evolution works. Arthropods have to have complimentary genitals, so little change in those can lead to the raise of new species.


Then why not in mammals and butterflies and birds???

There’re many twin species in mammals and birds, and surely butterflies have a lot of stuff where you need genitals. Mammals and birds are much bigger animals and surely they have slightly different laws of speciation and overall, they need much more space. I wouldn’t call empids or old world warblers easy to id, or rodents like e.g. Acomys.

Welcome to the real world. This is how it is – some creatures are very easy to ID, some are very difficult to ID. There is no “why”. Nature/DNA does what it wants to do, and we come trailing along behind it trying to make sense of it.

I would recommend doing your best with the easier things, and leaving the really tough things for the experts.

Of course in general the tiny things are more difficult, because we can’t see them very well without a microscope to see the relevant details.

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There’s probably a couple of other reasons why certain groups are harder than others. The first would be size – not just because of the difficulty in seeing them, but because the world’s bigger when you’re a millimeter long than when you’re the size of an elephant, so there’s room for a lot more species. The second reason is that certain groups (birds are a great example) use very similar sensory suites to ours – lots of visual and aural stimuli, with smell being much less important. Thus the signals that those species develop as they speciate are likely to be ones we can easily detect. Species that use smell to a larger extent are going to be harder for us to distinguish because we aren’t detecting their signals.


Oh! If you want to read about specializations for identifying things, read this book:
“The Lost Species - Great Expeditions in the Collections of Natural History Museums” by Christopher Kemp.

I just finished a chapter on nematodes/roundworms. Crazy! There are experts on just about everything out there.

Smaller living things can change quicker than larger things. So, beetles that get isolated on a mountaintop can change/adjust/adapt to a habitat faster than something like elephants. Beetles reproduce a lot faster. So, more species can develop in a lot shorter period of time. Elephants take time to go through a few generations. So, changes take longer. So, there are fewer species.

Other interesting things a little bit off the main topic:

A lot of people are raising monarch butterflies, and then releasing them. But, researchers have found that, if a person raises them in small cages and doesn’t give a batch of butterflies a large enclosure with a lot of flying space that simulates a more natural habitat, they will develop smaller, rounder wings to adapt to the small flying area. And, they cannot migrate. So, the raising in small cages actually hurts the species in one way. (It is good that people care and want to do something. So, it is hard to criticize them. But, the research needs to be applied to help the species.)

It has also been found that, captive parrots will develop smaller, rounder wings if they aren’t given adequate flying areas. They lose the ability to fly long distances But, this takes a few generations. Change happens in nature.


We’re primarily visual creatures. Other species that use vision to distinguish their species from others for mating, like most birds, are visually different and are easy for us to identify. Some groups of birds (like Empidonax flycatchers) use primarily song and habitat and look alike, and we find them hard. Many, many mammals, insects, etc., use scent. We’re pretty much blind to scent and have to use other details.

Then there’s the size thing. Very little organisms are likely to be hard for us to ID, other things being equal. Small organisms that use scent to distinguish their species? Really, really hard.


Time and space are surely two important factors and have been mentioned above.
Allopatric speciation (the rise of different species from one parent species in different locations) is much easier in organisms that do not need a lot of space, compared to larger mirgratory species (many birds, big mammals…).
Also, to evolve there must be a certain set of variation within a species, which is also easier to accumulate the more generations you produce. Talk about spiders and insects with mostly short generation cycles compared to (comparably) long-lived species with few offspring like mammals or birds.

As has been mentioned above, sexual selection also operates differently in many species than what we ourselfs experience. Especially in the small critters with often quite complicated genital structures on both ends even small variations might lead to decreased offspring or even an incompatibility and at times to separate species. That is, why in many cases genital examination in e.g. spiders can reveal different species that otherwise might look a lot alike.

Organisms that more recently diverged from each other will usually be more difficult to identify. An example would be Alder and Willow Flycatcher.

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I think the size of organisms make a big difference, however why some animals have a smaller genus I’m not sure.

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Years ago I overheard a conversation at Point Pelee between a frustrated newbie and one of the birding sages who hang out there during spring migration (might have been Bob Bateman). The newbie was lamenting how every time he came up with a cool ID it turned out to be wrong. The sage responded along the lines of “yeah, it’s a good idea to get as much of the really hard stuff on your list as possible before you figure out what you’re doing.”


yep… you didn’t evolve microscopes for eyes! Largely it is size/visibility of the characters that can differentiate between certain similar taxa.

But it also comes down to how much is known about each taxa by the various participants, and even further to how well defined the taxons are… many insect descriptions hail from the mid to late 1800s, and in the case of spiders for example, the understanding of their morphology has changed considerably since that time, and consequently much of the taxonomy (eg here in NZ) needs to be revised. This is happening currently, but there is a huge amount of work to do and so few people skilled, resourced and able to undertake it

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To an extent. But then, how long did it take for scientists to realize that chimpanzees and bonobos were different species? Or the bush elephant and forest elephant?

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