Cylindrarctus sp.

Pilopius sp. Reichenbachia sp. Cylindrartus sp. Euplectine Pilopius palps closeup Teneral Reichenbachia sp. Reichenbachia sp.

Pselaphid Beetles

So what's so special about a subfamily of straw-colored beetles no bigger than a grain of rice? I consider them to be one of the great mysteries of biology. It's a mystery whose answer is probably in that vacant lot near your house, no matter where you live, yet no one has solved it.

There are thousands of species of pselaphid beetles, way more than there are species of, say, mammals. There are probably a few species that live near you. But the are small and rarely found.

Now people don't care much about small things, but we do know a lot about them. Take ants, for instance.

There are ants in your neighborhood (unless you live very high up or in the polar regions) and you can find them just about any day, and you can identify them quite definitely.

But pselaphid beetles are super rare, or at least rarely found. I have spent countless hours sifting through soil samples, checking light traps, looking through grass clumps and rotten logs and I've only found a few dozen over many years.

Yet I've found them at streetlights. I've found them in leaf litter in vacant lots. Not exotic locations, but wherever I've found them, I've found them only once! They are all over but super hard to find!

It gets weirder.

All beetles develop from larvae. You can collects soil samples and find larvae for all sorts of things. Of all the insects we know about, we usually know what the larvae look like and how to find them. Of the thousands of species of pselaphid beetles, only twelve larvae have been found! No one's ever seen them lay eggs. No one knows where most of them live. Some have been found living with ants. Still, we have no larvae of these.

  • So where do the live?
  • What do they eat?
  • Where do they lay their eggs?
  • Where are the larvae?
  • Are they really super rare or are we not looking in the right place?
No one knows!

So there's the mystery, all around you, find the answer!

I started this web page in the mid-90s, when the web was young, before wikipedia, taking crappy low-res digital pictures. I have since given up solving this mystery. I have poured hours into it to no avail. Not in vain though. I have a much better appreciation of the small world of animals and plants around us, below our feet. I was able to keep a few individuals of Tmesiphorus carinatus alive for a few weeks. Maybe people have made progress on this, I doubt it. It's a mystery few care about.

Below is some general info on pselaphids, largely as I wrote it in the 90s. Wikipedia's page on it is good, I trust you can find that. I will add any resources I find on the web.

So he quest is there. WIll you take it up? Do you have the insight, ingenuity and imagination to solve the mystery of the pselaphids?


  • Phylum Arthropoda (insects, spiders, crustaceans and more)
    • Class Hexapoda (the insects)
      • Order Coleoptera (the beetles)
        • Family Staphylinidae (rove beetles)
          • Subfamily Pselaphinae

Commonly known as Ant-loving Beetles, Short-Winged Mold Beetles, or simply, pselaphids)

Until recently, they were classified in their own family Pselaphidae (see Newton & Thayer 1995). You will still see many references to them under this name.

Diversity: There are 712 species in the USA, and over 8,000 worldwide. To give you an idea how big this is there are roughly 4,000 species of mammals, 6,000 species of reptiles, and 8,000 species of ants. Beetles are the most diverse group of organisms, with roughly 290,000 species. Pselaphid beetles are found all over the world.

Description:Pselaphids are small beetles, about 0.7mm to 4.5mm, or from the size of a small mosquito to the size of a grain of rice. They all tend to be straw colored (see the pictures below). In the wild they look a little like slow-moving ants. More technically, like rove beetles (Staphylinidae), their elytra are short exposing much of the upper surface of the abdomen, but they are different from rove beetles in that their abdomens are usually not flexible, their antennae are clubbed, and their abdomens tend to be broader than their heads. For further help in identifying pselaphids and other beetle families see Peterson's Field Guide to Beetles. For a more technical key to the beetles see the standard entomological textbook Introduction to Insects.

Pselaphids are very distinctive, but it can be difficult to identify them to the genus level. A very powerful hand lens, jeweler's visor, or best of all, a dissecting microscope will be helpful in identification. The best key to the genera of the United States was made by Donald S. Chandler and appears in the Soil Biology Guide. There are other good keys such as Arnett's Beetles of the United States.

If you're interested in knowing what species it is, there are keys to many genera. If you contact me, I will be glad to tell you if there is a key for the genera you are interested. Better yet, you can send me the specimens. I always love to see new specimens. If it's an "easy one' I might be able to identify it, otherwise I would send it on to one of two experts on pselaphids, Dr. Chris Carlton or Dr. Don Chandler. You may wish to contact them directly.

Natural History: The natural history of Pselaphids is poorly understood, but they can be divided into species that live with ants and free-living species. This is actually a continuum, with some species occasionally being found with ants. The species that live with ants are somehow able to live within the colony without being attacked as any other insect would be. They may fool the ants into thinking they are other ants, or just some inert matter or a dead insect. The ants may feed the beetles directly, as they would any other ant in the colony, or the pselaphids may eat the brood of the ants. I find the interaction of pselaphids with ants very interesting, and it is the subject of my research.

Many other pselaphids are free living, occurring in a variety of habitats that share a few characteristics, namely, they are very moist and they contain decaying plant material. Many species are found in the leaf litter, but they also occur in rotten logs, at the bases of grass clumps, and under boards and rocks. Some species are specialized to live in caves, on mountains, in bogs, on the beach, and in the desert.

All free-living pselaphids eat other smaller animals, such as small insects and their larvae, worms, and mites. Actually, we don't know exactly what most pselaphid species eat, but judging from their similar mouthparts (designed for catching prey, not grinding plants or fungus) and from what we know a few of them eat, we can be pretty sure that the vast majority eat small animals.

Abundance: Unlike insects like mosquitoes or aphids, pselaphids are not abundant. They are small and they live in hidden habitats, thus even people who collect insects do not often encounter them. There are some species that are amazingly scarce. They are known from only one or a few specimens and nothing more. Many are attracted to lights, as moths are, but we don't know where they live in the wild.

Life History: Here is where our lack of knowledge of these beetles really shows. For the over 8,000 species known in the world, only about 12 larvae have been described. Many people have looked very hard for these larvae and not found any. Are we looking in the wrong places? Are the larvae very fast-developing? We don't know the answers. To date, no one has uncovered the complete life history of any pselaphid.

Collecting: No matter where you live, you are probably just a short trip away from a spot where pselaphids live, they may even live in that vacant lot across the street. But as they are small, scarce, and live in hidden places, they can be hard to collect. You rarely just see them in the wild. Here are a few collecting methods.

Hand Collecting: This is the most time consuming, least productive, yet most rewarding method. When you find a pselaphid in the wild, you have a lot of information about where they are found naturally, that you might not get with other methods. Also I like to try and keep them alive and see what they eat and how they behave. Most likely, any observations on behavior or diet you make have never been made before and are valuable scientific information. To find them by hand you need a keen eye. Watch for slow moving, ant-like insects in the following places: in rotten logs, under boards in fields, under rocks (on their underside too) and in ant nests. Look carefully, as some pselaphids 'play dead' when first disturbed. Looking in leaf litter is too hard, although if you sift the litter through ¼ or 1/8 inch hardware cloth first, you might find something.

Berlese (burr-LAY-zee) funnel: This is the most productive method of finding pselaphids. To do this, first collect nice moist leaf litter (not sopping wet), and sift it through a ¼ or 1/8 hardware cloth sifter. This will give you a pile of sawdust-like material that may contain a lot of insects and other arthropods running around. You put this in a berlese funnel and let it 'run' for a few nights. For a detailed description on what a berlese funnel is and how to make one see either Peterson's Field Guide to Beetles or Introduction to Insects. Essentially all it is is a funnel with a screen in the middle, and the sifted litter is placed on the screen and a light bulb is placed above. The heat from the light bulb dries out the litter and drives the arthropods out the bottom of the litter, down the funnel, to a dish of alcohol below.

Culture: We know very little about what these beetles eat, how they mate and raise their young. It is impractical to observe these creatures in the wild, so raising them in captivity is the only option left. Just about any observation you can make on a pselaphid species living near you is likely to be new to science.

Housing: Pselaphids, more than anything else, require high humidity. They can be easily kept in a small container, such as a baby-food jar, plastic cottage cheese container, or small plastic petri dishes if you can get them.

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